Excited state electron affinity calculations for aluminum
Hussein, Adnan Yousif
2017-08-01
Excited states of negative aluminum ion are reviewed, and calculations of electron affinities of the states (3s^23p^2)^1D and (3s3p^3){^5}{S}° relative to the (3s^23p)^2P° and (3s3p^2)^4P respectively of the neutral aluminum atom are reported in the framework of nonrelativistic configuration interaction (CI) method. A priori selected CI (SCI) with truncation energy error (Bunge in J Chem Phys 125:014107, 2006) and CI by parts (Bunge and Carbó-Dorca in J Chem Phys 125:014108, 2006) are used to approximate the valence nonrelativistic energy. Systematic studies of convergence of electron affinity with respect to the CI excitation level are reported. The calculated value of the electron affinity for ^1D state is 78.675(3) meV. Detailed Calculations on the ^5S°c state reveals that is 1216.8166(3) meV below the ^4P state.
Su, Neil Qiang; Xu, Xin
2015-10-13
An integration approach is developed to calculate ionization potentials (IPs), and electron affinities (EAs), which is an extension of the D-ΔMBPT(2) method [A. Beste et al., J. Chem. Phys. 2013, 138, 074101]. The latter is an extension of the single-point method of Cohen et al. [A. J. Cohen et al., J. Chem. Theory Comput. 2009, 5, 786] from the perspective of fractional charges. While relaxation effects were included only at the Hartree-Fock (HF) level in the previous methods, such effects are fully taken into account in the present method up to the second-order Møller-Plesset (MP2) level. This is made possible by deriving the full MP2 energy gradient, with respect to the orbital occupation numbers, which is solved through the coupled-perturbed HF (CP-HF) equations.
Su, Neil Qiang; Xu, Xin
2016-05-10
Recently, we have developed an integration approach for the calculations of ionization potentials (IPs) and electron affinities (EAs) of molecular systems at the level of second-order Møller-Plesset (MP2) (Su, N. Q.; Xu, X. J. Chem. Theory Comput. 11, 4677, 2015), where the full MP2 energy gradient with respect to the orbital occupation numbers was derived but only at integer occupations. The theory is completed here to cover the fractional occupation systems, such that Slater's transition state concept can be used to have accurate predictions of IPs and EAs. Antisymmetrized Goldstone diagrams have been employed for interpretations and better understanding of the derived equations, where two additional rules were introduced in the present work specifically for hole or particle lines with fractional occupation numbers.
G4MP2, DFT and CBS-Q calculation of proton and electron affinities ...
Indian Academy of Sciences (India)
icals in the production of pharmaceuticals, detergents, emulsifiers, polishes, corrosion inhibitors and chemical intermediates.11 DEA is used to synthesize ..... connected to electron donor groups (ethyl or ethanol), is easier than the carbon atom. Therefore, the car- bon and nitrogen atoms form a bond between them-.
Electron affinity of liquid water
Energy Technology Data Exchange (ETDEWEB)
Gaiduk, Alex P.; Pham, Tuan Anh; Govoni, Marco; Paesani, Francesco; Galli, Giulia
2018-01-16
Understanding redox and photochemical reactions in aqueous environments requires a precise knowledge of the ionization potential and electron affinity of liquid water. The former has been measured, but not the latter. We predict the electron affinity of liquid water and of its surface from first principles, coupling path-integral molecular dynamics with ab initio potentials, and many-body perturbation theory. Our results for the surface (0.8 eV) agree well with recent pump-probe spectroscopy measurements on amorphous ice. Those for the bulk (0.1–0.3 eV) differ from several estimates adopted in the literature, which we critically revisit. We show that the ionization potential of the bulk and surface are almost identical; instead their electron affinities differ substantially, with the conduction band edge of the surface much deeper in energy than that of the bulk. We also discuss the significant impact of nuclear quantum effects on the fundamental gap and band edges of the liquid.
Directory of Open Access Journals (Sweden)
Ala Aldin M. H. M. Darghouth
2015-12-01
Full Text Available Ionization potentials (IPs and electron affinities (EAs are important quantities input into most models for calculating the open-circuit voltage (Voc of organic solar cells. We assess the semi-empirical density-functional tight-binding (DFTB method with the third-order self-consistent charge (SCC correction and the 3ob parameter set (the third-order DFTB (DFTB3 organic and biochemistry parameter set against experiments (for smaller molecules and against first-principles GW (Green’s function, G, times the screened potential, W calculations (for larger molecules of interest in organic electronics for the calculation of IPs and EAs. Since GW calculations are relatively new for molecules of this size, we have also taken care to validate these calculations against experiments. As expected, DFTB is found to behave very much like density-functional theory (DFT, but with some loss of accuracy in predicting IPs and EAs. For small molecules, the best results were found with ΔSCF (Δ self-consistent field SCC-DFTB calculations for first IPs (good to ± 0.649 eV. When considering several IPs of the same molecule, it is convenient to use the negative of the orbital energies (which we refer to as Koopmans’ theorem (KT IPs as an indication of trends. Linear regression analysis shows that KT SCC-DFTB IPs are nearly as accurate as ΔSCF SCC-DFTB eigenvalues (± 0.852 eV for first IPs, but ± 0.706 eV for all of the IPs considered here for small molecules. For larger molecules, SCC-DFTB was also the ideal choice with IP/EA errors of ± 0.489/0.740 eV from ΔSCF calculations and of ± 0.326/0.458 eV from (KT orbital energies. Interestingly, the linear least squares fit for the KT IPs of the larger molecules also proves to have good predictive value for the lower energy KT IPs of smaller molecules, with significant deviations appearing only for IPs of 15–20 eV or larger. We believe that this quantitative analysis of errors in SCC-DFTB IPs and EAs may be of
Electron attachment and detachment: Electron affinities of isomers of trifluoromethylbenzonitrile
Miller, Thomas M.; Viggiano, A. A.; Friedman, Jeffrey F.; Van Doren, Jane M.
2004-11-01
Rate constants for electron attachment to the three isomers of trifluoromethylbenzonitrile [(CF3)(CN)C6H4, or TFMBN] were measured over the temperature range of 303-463 K in a 133-Pa He buffer gas, using a flowing-afterglow Langmuir-probe apparatus. At 303 K, the measured attachment rate constants are 9.0×10-8 (o-TFMBN), 5.5×10-8 (m-TFMBN), and 8.9×10-8 cm3 s-1 (p-TFMBN), estimated accurate to ±25%. The attachment process formed only the parent anion in all three cases. Thermal electron detachment was observed for all three anion isomers, and rate constants for this reverse process were also measured. From the attachment and detachment results, the electron affinities of the three isomers of TFMBN were determined to be 0.70(o-TFMBN), 0.67(m-TFMBN), and 0.83 eV (p-TFMBN), all ±0.05 eV. G3(MP2) [Gaussian-3 calculations with reduced Møller-Plesset orders (MP2)] calculations were carried out for the neutrals and anions. Electron affinities derived from these calculations are in good agreement with the experimental values.
Electron-trapping polycrystalline materials with negative electron affinity.
McKenna, Keith P; Shluger, Alexander L
2008-11-01
The trapping of electrons by grain boundaries in semiconducting and insulating materials is important for a wide range of physical problems, for example, relating to: electroceramic materials with applications as sensors, varistors and fuel cells, reliability issues for solar cell and semiconductor technologies and electromagnetic seismic phenomena in the Earth's crust. Surprisingly, considering their relevance for applications and abundance in the environment, there have been few experimental or theoretical studies of the electron trapping properties of grain boundaries in highly ionic materials such as the alkaline earth metal oxides and alkali halides. Here we demonstrate, by first-principles calculations on MgO, LiF and NaCl, a qualitatively new type of electron trapping at grain boundaries. This trapping is associated with the negative electron affinity of these materials and is unusual as the electron is confined in the empty space inside the dislocation cores.
Electronics Environmental Benefits Calculator
U.S. Environmental Protection Agency — The Electronics Environmental Benefits Calculator (EEBC) was developed to assist organizations in estimating the environmental benefits of greening their purchase,...
Isotope shift in the electron affinity of lithium
Bubin, Sergiy; Komasa, Jacek; Stanke, Monika; Adamowicz, Ludwik
2009-12-01
Very accurate electron affinity (EA) calculations of L6i and L7i (and L∞i) have been performed using explicitly correlated Gaussian functions and a variational approach that explicitly includes the nuclear motion in the calculations (i.e., the approach that does not assume the Born-Oppenheimer approximation). The leading relativistic and quantum electrodynamics corrections to the electron affinities were also calculated. The results are the most accurate theoretical values obtained for the studied systems to date. Our best estimates of the L7i and L6i EAs are 4984.9842(30) and 4984.9015(30) cm-1, respectively, and of the L7i/L6i EA isotope shift is 0.0827 cm-1.
An efficient computational method for calculating ligand binding affinities.
Directory of Open Access Journals (Sweden)
Atsushi Suenaga
Full Text Available Virtual compound screening using molecular docking is widely used in the discovery of new lead compounds for drug design. However, the docking scores are not sufficiently precise to represent the protein-ligand binding affinity. Here, we developed an efficient computational method for calculating protein-ligand binding affinity, which is based on molecular mechanics generalized Born/surface area (MM-GBSA calculations and Jarzynski identity. Jarzynski identity is an exact relation between free energy differences and the work done through non-equilibrium process, and MM-GBSA is a semimacroscopic approach to calculate the potential energy. To calculate the work distribution when a ligand is pulled out of its binding site, multiple protein-ligand conformations are randomly generated as an alternative to performing an explicit single-molecule pulling simulation. We assessed the new method, multiple random conformation/MM-GBSA (MRC-MMGBSA, by evaluating ligand-binding affinities (scores for four target proteins, and comparing these scores with experimental data. The calculated scores were qualitatively in good agreement with the experimental binding affinities, and the optimal docking structure could be determined by ranking the scores of the multiple docking poses obtained by the molecular docking process. Furthermore, the scores showed a strong linear response to experimental binding free energies, so that the free energy difference of the ligand binding (ΔΔG could be calculated by linear scaling of the scores. The error of calculated ΔΔG was within ≈ ± 1.5 kcal.mol(-1 of the experimental values. Particularly, in the case of flexible target proteins, the MRC-MMGBSA scores were more effective in ranking ligands than those generated by the MM-GBSA method using a single protein-ligand conformation. The results suggest that, owing to its lower computational costs and greater accuracy, the MRC-MMGBSA offers efficient means to rank the ligands, in
Isotope shift on the chlorine electron affinity revisited by an MCHF/CI approach
Carette, Thomas
2013-01-01
Today, the electron affinity is experimentally well known for most of the elements and is a useful guideline for developing ab initio computational methods. However, the measurements of isotope shifts on the electron affinity are limited by both resolution and sensitivity. In this context, theory eventually contributes to the knowledge and understanding of atomic structures, even though correlation plays a dominant role in negative ions properties and, particularly, in the calculation of the specific mass shift contribution. The present study solves the longstanding discrepancy between calculated and measured specific mass shifts on the electron affinity of chlorine (Phys. Rev. A 51 (1995) 231)
Electron affinity and excited states of methylglyoxal
Dauletyarov, Yerbolat; Dixon, Andrew R.; Wallace, Adam A.; Sanov, Andrei
2017-07-01
Using photoelectron imaging spectroscopy, we characterized the anion of methylglyoxal (X2A″ electronic state) and three lowest electronic states of the neutral methylglyoxal molecule: the closed-shell singlet ground state (X1A'), the lowest triplet state (a3A″), and the open-shell singlet state (A1A″). The adiabatic electron affinity (EA) of the ground state, EA(X1A') = 0.87(1) eV, spectroscopically determined for the first time, compares to 1.10(2) eV for unsubstituted glyoxal. The EAs (adiabatic attachment energies) of two excited states of methylglyoxal were also determined: EA(a3A″) = 3.27(2) eV and EA(A1A″) = 3.614(9) eV. The photodetachment of the anion to each of these two states produces the neutral species near the respective structural equilibria; hence, the a3A″ ← X2A″ and A1A″ ← X2A″ photodetachment transitions are dominated by intense peaks at their respective origins. The lowest-energy photodetachment transition, on the other hand, involves significant geometry relaxation in the X1A' state, which corresponds to a 60° internal rotation of the methyl group, compared to the anion structure. Accordingly, the X1A' ← X2A″ transition is characterized as a broad, congested band, whose vertical detachment energy, VDE = 1.20(4) eV, significantly exceeds the adiabatic EA. The experimental results are in excellent agreement with the ab initio predictions using several equation-of-motion methodologies, combined with coupled-cluster theory.
Calculations on Lie Algebra of the Group of Affine Symplectomorphisms
Directory of Open Access Journals (Sweden)
Zuhier Altawallbeh
2017-01-01
Full Text Available We find the image of the affine symplectic Lie algebra gn from the Leibniz homology HL⁎(gn to the Lie algebra homology H⁎Lie(gn. The result shows that the image is the exterior algebra ∧⁎(wn generated by the forms wn=∑i=1n(∂/∂xi∧∂/∂yi. Given the relevance of Hochschild homology to string topology and to get more interesting applications, we show that such a map is of potential interest in string topology and homological algebra by taking into account that the Hochschild homology HH⁎-1(U(gn is isomorphic to H⁎-1Lie(gn,U(gnad. Explicitly, we use the alternation of multilinear map, in our elements, to do certain calculations.
Kalimullina, L. R.; Nafikova, E. P.; Asfandiarov, N. L.; Chizhov, Yu. V.; Baibulova, G. Sh.; Zhdanov, E. R.; Gadiev, R. M.
2015-03-01
A number of compounds related to quinone derivatives is investigated by means of density functional theory in the B3LYP/6-31G(d) mode. Vertical electron affinity E va and/or electron affinity E a for the investigated compounds are known from experiments. The correlation between the calculated energies of π* molecular orbitals with the E va values measured via electron transmission spectroscopy is determined with a coefficient of 0.96. It is established that theoretical values of the adiabatic electron affinity, calculated as the difference between the total energies of a neutral molecule and a radical anion, correlate with E a values determined from electron transfer experiments with a correlation coefficient of 0.996.
Gas phase adiabatic electron affinities of cyclopenta-fused polycyclic aromatic hydrocarbons
Todorov, P.D.; Koper, C.; van Lenthe, J.H.; Jenneskens, L.W.
2008-01-01
The B3LYP/DZP++ adiabatic electron affinity (AEA) of nine (non)-alternant polycyclic aromatic hydrocarbons are reported and discussed. Calculations became feasible for molecules this size by projecting out the near-linearly dependent part of the one-electron basis. Non-alternant PAH consisting of an
Electronics reliability calculation and design
Dummer, Geoffrey W A; Hiller, N
1966-01-01
Electronics Reliability-Calculation and Design provides an introduction to the fundamental concepts of reliability. The increasing complexity of electronic equipment has made problems in designing and manufacturing a reliable product more and more difficult. Specific techniques have been developed that enable designers to integrate reliability into their products, and reliability has become a science in its own right. The book begins with a discussion of basic mathematical and statistical concepts, including arithmetic mean, frequency distribution, median and mode, scatter or dispersion of mea
Directory of Open Access Journals (Sweden)
José Carlos B. de Lima
2010-01-01
Full Text Available The CBS-4M, CBS-QB3, G2, G2(MP2, G3 and G3(MP2 model chemistry methods have been used to calculate proton and electron affinities for a set of molecular and atomic systems. Agreement with the experimental value for these electronic properties is quite good considering the uncertainty in the experimental data. A comparison among the six theories using statistical analysis (average value, standard deviation and root-mean-square showed a better performance of CBS-QB3 to obtain these properties.
Tunable electron affinity with electronic band alignment of solution processed dielectric
Mondal, Sandip; Venkataraman, V.
2017-07-01
We report the tunability of the electronic band structure, especially the electron affinity, of an all-inorganic precursor processed sol-gel aluminium oxide phosphate dielectric by the influence of processing temperature. The dielectric offers tunable electron affinity ranging from 1.42 eV to 0.72 eV with the change in processing temperature from as-prepared to 1000 °C, respectively. The remarkable change in electron affinity is ascribed to the variation in the bulk oxygen concentration in solution processed oxide. As a result, the leakage current of the dielectric is affected significantly by a factor of ˜103.
Coe, Jeremy P; Taylor, Daniel J; Paterson, Martin J
2013-05-15
The method of Monte Carlo configuration interaction (MCCI) (Greer, J. Chem. Phys. 1995a, 103, 1821; Tong, Nolan, Cheng, and Greer, Comp. Phys. Comm. 2000, 142, 132) is applied to the calculation of multipole moments. We look at the ground and excited state dipole moments in carbon monoxide. We then consider the dipole of NO, the quadrupole of N2 and of BH. An octupole of methane is also calculated. We consider experimental geometries and also stretched bonds. We show that these nonvariational quantities may be found to relatively good accuracy when compared with full configuration interaction results, yet using only a small fraction of the full configuration interaction space. MCCI results in the aug-cc-pVDZ basis are seen to generally have reasonably good agreement with experiment. We also investigate the performance of MCCI when applied to ionisation energies and electron affinities of atoms in an aug-cc-pVQZ basis. We compare the MCCI results with full configuration interaction quantum Monte Carlo (Booth and Alavi, J. Chem. Phys. 2010, 132, 174104; Cleland, Booth, and Alavi, J. Chem. Phys. 2011, 134, 024112) and "exact" nonrelativistic results (Booth and Alavi, J. Chem. Phys. 2010, 132, 174104; Cleland, Booth, and Alavi, J. Chem. Phys. 2011, 134, 024112). We show that MCCI could be a useful alternative for the calculation of atomic ionisation energies however electron affinities appear much more challenging for MCCI. Due to the small magnitude of the electron affinities their percentage errors can be high, but with regards to absolute errors MCCI performs similarly for ionisation energies and electron affinities. Copyright © 2013 Wiley Periodicals, Inc.
Yoshida, Hiroyuki
2014-04-01
Electron affinity is a fundamental energy parameter of materials. In organic semiconductors, the electron affinity is closely related to electron conduction. It is not only important to understand fundamental electronic processes in organic solids, but it is also indispensable for research and development of organic semiconductor devices such as organic light-emitting diodes and organic photovoltaic cells. However, there has been no experimental technique for examining the electron affinity of organic materials that meets the requirements of such research. Recently, a new method, called low-energy inverse-photoemission spectroscopy, has been developed. A beam of low-energy electrons is focused onto the sample surface, and photons emitted owing to the radiative transition to unoccupied states are then detected. From the onset of the spectral intensity, the electron affinity is determined within an uncertainty of 0.1 eV. Unlike in conventional inverse-photoemission spectroscopy, sample damage is negligible and the resolution is improved by a factor of 2. The principle of the method and several applications are reported.
Energy Technology Data Exchange (ETDEWEB)
Peng, Bo; Govind, Niranjan; Aprà, Edoardo; Klemm, Michael; Hammond, Jeff R.; Kowalski, Karol
2017-02-03
In this paper we apply equation-of-motion coupled cluster (EOMCC) methods in studies of vertical ionization potentials (IP) and electron affinities (EA) for sin- gled walled carbon nanotubes. EOMCC formulations for ionization potentials and electron affinities employing excitation manifolds spanned by single and double ex- citations (IP/EA-EOMCCSD) are used to study IPs and EAs of nanotubes as a function of nanotube length. Several armchair nanotubes corresponding to C20nH20 models with n = 2 - 6 have been used in benchmark calculations. In agreement with previous studies, we demonstrate that the electronegativity of C20nH20 systems remains, to a large extent, independent of nanotube length. We also compare IP/EA- EOMCCSD results with those obtained with the coupled cluster models with single and double excitations corrected by perturbative triples, CCSD(T), and density func- tional theory (DFT) using global and range-separated hybrid exchange-correlation functionals.
Block Tridiagonal Matrices in Electronic Structure Calculations
DEFF Research Database (Denmark)
Petersen, Dan Erik
This thesis focuses on some of the numerical aspects of the treatment of the electronic structure problem, in particular that of determining the ground state electronic density for the non–equilibrium Green’s function formulation of two–probe systems and the calculation of transmission...
A corrector for spacecraft calculated electron moments
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J. Geach
2005-03-01
Full Text Available We present the application of a numerical method to correct electron moments calculated on-board spacecraft from the effects of potential broadening and energy range truncation. Assuming a shape for the natural distribution of the ambient plasma and employing the scalar approximation, the on-board moments can be represented as non-linear integral functions of the underlying distribution. We have implemented an algorithm which inverts this system successfully over a wide range of parameters for an assumed underlying drifting Maxwellian distribution. The outputs of the solver are the corrected electron plasma temperature Te, density Ne and velocity vector Ve. We also make an estimation of the temperature anisotropy A of the distribution. We present corrected moment data from Cluster's PEACE experiment for a range of plasma environments and make comparisons with electron and ion data from other Cluster instruments, as well as the equivalent ground-based calculations using full 3-D distribution PEACE telemetry.
Zou, Tiefang; Peng, Haitao; Cai, Ming; Wu, Hequan; Hu, Lin
2016-09-01
In order to analyze the uncertainty of a reconstructed result, the Interval Algorithm (IA), the Affine Arithmetic (AA) and the Modified Affine Arithmetic (MAA) were introduced firstly, and then a Taylor-Affine Arithmetic (TAA) was proposed based on the MAA and Taylor series. Steps of the TAA, especially in analyzing uncertainty of a simulation result were given. Through the preceding five numerical cases, its application was demonstrated and its feasibility was validated. Results showed that no matter other methods (The IA, AA, the Upper and Lower bound Method, the Finite Difference Method) work well or bad, the TAA work well, even under the condition that the MAA cannot work in some cases because of the division/root operation in these models. Furthermore, in order to make sure that the result obtained from the TAA can be very close to the accurate interval, a simple algorithm was proposed based on the sub-interval technique, its feasibility was validated by two other numerical cases. Finally, a vehicle-pedestrian test was given to demonstrate the application of the TAA in practice. In the vehicle-pedestrian test, the interval [35.5, 39.1]km/h of the impact velocity can be calculated according to steps of the TAA, such interval information will be more useful in accident responsibility identification than a single number. This study will provide a new alternative method for uncertainty analysis in accident reconstruction. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.
Electron mobility calculation for graphene on substrates
Energy Technology Data Exchange (ETDEWEB)
Hirai, Hideki; Ogawa, Matsuto [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1, Rokko-dai, Nada-ku, Kobe 657-8501 (Japan); Tsuchiya, Hideaki, E-mail: tsuchiya@eedept.kobe-u.ac.jp [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1, Rokko-dai, Nada-ku, Kobe 657-8501 (Japan); Japan Science and Technology Agency, CREST, Chiyoda, Tokyo 102-0075 (Japan); Kamakura, Yoshinari; Mori, Nobuya [Japan Science and Technology Agency, CREST, Chiyoda, Tokyo 102-0075 (Japan); Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan)
2014-08-28
By a semiclassical Monte Carlo method, the electron mobility in graphene is calculated for three different substrates: SiO{sub 2}, HfO{sub 2}, and hexagonal boron nitride (h-BN). The calculations account for polar and non-polar surface optical phonon (OP) scatterings induced by the substrates and charged impurity (CI) scattering, in addition to intrinsic phonon scattering in pristine graphene. It is found that HfO{sub 2} is unsuitable as a substrate, because the surface OP scattering of the substrate significantly degrades the electron mobility. The mobility on the SiO{sub 2} and h-BN substrates decreases due to CI scattering. However, the mobility on the h-BN substrate exhibits a high electron mobility of 170 000 cm{sup 2}/(V·s) for electron densities less than 10{sup 12 }cm{sup −2}. Therefore, h-BN should be an appealing substrate for graphene devices, as confirmed experimentally.
Accurate Electron Affinity of Iron and Fine Structures of Negative Iron ions.
Chen, Xiaolin; Luo, Zhihong; Li, Jiaming; Ning, Chuangang
2016-05-03
Ionization potential (IP) is defined as the amount of energy required to remove the most loosely bound electron of an atom, while electron affinity (EA) is defined as the amount of energy released when an electron is attached to a neutral atom. Both IP and EA are critical for understanding chemical properties of an element. In contrast to accurate IPs and structures of neutral atoms, EAs and structures of negative ions are relatively unexplored, especially for the transition metal anions. Here, we report the accurate EA value of Fe and fine structures of Fe(-) using the slow electron velocity imaging method. These measurements yield a very accurate EA value of Fe, 1235.93(28) cm(-1) or 153.236(34) meV. The fine structures of Fe(-) were also successfully resolved. The present work provides a reliable benchmark for theoretical calculations, and also paves the way for improving the EA measurements of other transition metal atoms to the sub cm(-1) accuracy.
New concept for the calculation of the trace element affinity in coal
Energy Technology Data Exchange (ETDEWEB)
Klika, Z.; Kolomaznik, I. [VSB-Technical University Ostrava, Ostrava-Poruba (Czech Republic)
2000-05-01
The present models for the calculation of the trace element affinity between organic and inorganic parts of coal are critically evaluated and a new concept of calculation is proposed. This new concept of calculation is based on the experimental data characterising coal fractions separated from coal samples using sink-float technique. It consists in the calculation of (a) organic element association (OEA) supposing constant concentration of the element in organic phase and (b) maximal organic element association (OEA{sub max}) supposing maximal possible concentration of the element in the organic phase of all coal fractions. For one coal sample OEA and OEA{sub max} are calculated. It must be valid that OEA {le} OEA{sub max}. This relation is not true for some elements e.g. Ge and Ga, which usually have extremely high concentration in the lightest coal fraction. Contemporary with OEA the inorganic element association (IEA) is evaluated. Using least squares method the IEA can be recalculated among mineral groups present in coal. The model was successfully tested on one sample of bituminous coal and one sample of brown coal. 17 refs., 7 figs., 5 tabs.
Ye, Qun
2013-03-15
Several diazatetracene diimides with high electron affinity (up to 4.66 eV!) were prepared and well characterized. The LUMO energy level of these electron-deficient molecules was found to be closely related to their material stability. Compound 7 with ultrahigh electron affinity suffered from reduction and hydrolysis in the presence of silica gel or water. The stable compounds 3 and 6 showed n-channel FET behavior with an average electron mobility of 0.002 and 0.005 cm2 V-1 s-1, respectively, using a solution processing method. © 2013 American Chemical Society.
Borschevsky, A.; Pašteka, L. F.; Pershina, V.; Eliav, E.; Kaldor, U.
2015-02-01
Calculations of the first and second ionization potentials and electron affinities of superheavy elements 115-117 are presented. The calculations are performed in the framework of the Dirac-Coulomb Hamiltonian, and the results are corrected for the Breit and QED contributions. Correlation is treated by the relativistic coupled cluster approach with single, double, and perturbative triple excitations [CCSD(T)]. The same approach is used to calculate the ionization potentials and electron affinities of the lighter homologues, Bi, Po, and At. Comparison of the available experimental values for these atoms, namely, the first ionization potentials (IPs) of Bi, Po, and At and the second IP and EA of Bi, with our results shows excellent agreement, within a few hundredths of an eV, lending credence to our predictions for their superheavy homologues. High-accuracy predictions are also made for the second ionization potentials and electron affinities of Po and At, where no experiment is available.
Cobalamins uncovered by modern electronic structure calculations
DEFF Research Database (Denmark)
Kepp, Kasper Planeta; Ryde, Ulf
2009-01-01
This review describes how computational methods have contributed to the held of cobalamin chemistry since the start of the new millennium. Cobalamins are cobalt-dependent cofactors that are used for alkyl transfer and radical initiation by several classes of enzymes. Since the entry of modern...... electronic-structure calculations, in particular density functional methods, the understanding of the molecular mechanism of cobalamins has changed dramatically, going from a dominating view of trans-steric strain effects to a much more complex view involving an arsenal of catalytic strategies. Among...
Atomic Reference Data for Electronic Structure Calculations
Kotochigova, S; Shirley, E L
We have generated data for atomic electronic structure calculations, to provide a standard reference for results of specified accuracy under commonly used approximations. Results are presented here for total energies and orbital energy eigenvalues for all atoms from H to U, at microHartree accuracy in the total energy, as computed in the local-density approximation (LDA) the local-spin-density approximation (LSD); the relativistic local-density approximation (RLDA); and scalar-relativistic local-density approximation (ScRLDA).
Electronic Structure Calculations and the Ising Hamiltonian.
Xia, Rongxin; Bian, Teng; Kais, Sabre
2017-11-20
Obtaining exact solutions to the Schrödinger equation for atoms, molecules, and extended systems continues to be a "Holy Grail" problem which the fields of theoretical chemistry and physics have been striving to solve since inception. Recent breakthroughs have been made in the development of hardware-efficient quantum optimizers and coherent Ising machines capable of simulating hundreds of interacting spins with an Ising-type Hamiltonian. One of the most vital questions pertaining to these new devices is, "Can these machines be used to perform electronic structure calculations?" Within this work, we review the general procedure used by these devices and prove that there is an exact mapping between the electronic structure Hamiltonian and the Ising Hamiltonian. Additionally, we provide simulation results of the transformed Ising Hamiltonian for H2 , He2 , HeH+, and LiH molecules, which match the exact numerical calculations. This demonstrates that one can map the molecular Hamiltonian to an Ising-type Hamiltonian which could easily be implemented on currently available quantum hardware. This is an early step in developing generalized methods on such devices for chemical physics.
Calculation of fractional electron capture probabilities
Schoenfeld, E
1998-01-01
A 'Table of Radionuclides' is being prepared which will supersede the 'Table de Radionucleides' formerly issued by the LMRI/LPRI (France). In this effort it is desirable to have a uniform basis for calculating theoretical values of fractional electron capture probabilities. A table has been compiled which allows one to calculate conveniently and quickly the fractional probabilities P sub K , P sub L , P sub M , P sub N and P sub O , their ratios and the assigned uncertainties for allowed and non-unique first forbidden electron capture transitions of known transition energy for radionuclides with atomic numbers from Z=3 to 102. These results have been applied to a total of 28 transitions of 14 radionuclides ( sup 7 Be, sup 2 sup 2 Na, sup 5 sup 1 Cr, sup 5 sup 4 Mn, sup 5 sup 5 Fe, sup 6 sup 8 Ge , sup 6 sup 8 Ga, sup 7 sup 5 Se, sup 1 sup 0 sup 9 Cd, sup 1 sup 2 sup 5 I, sup 1 sup 3 sup 9 Ce, sup 1 sup 6 sup 9 Yb, sup 1 sup 9 sup 7 Hg, sup 2 sup 0 sup 2 Tl). The values are in reasonable agreement with measure...
Electron attachment and detachment, and the electron affinities of C5F5N and C5HF4N
Van Doren, Jane M.; Kerr, Donna M.; Miller, Thomas M.; Viggiano, A. A.
2005-09-01
Rate constants have been measured for electron attachment to C5F5N (297-433K) and to 2,3,5,6-C5HF4N (303K) using a flowing-afterglow Langmuir-probe apparatus (at a He gas pressure of 133Pa). In both cases only the parent anion was formed in the attachment process. The attachment rate constants measured at room temperature are 1.8±0.5×10-7 and 7±3×10-10cm-3s-1, respectively. Rate constants were also measured for thermal electron detachment from the parent anions of these molecules. For C5F5N- detachment is negligible at room temperature, but increases to 2530±890s-1 at 433K. For 2,3,5,6-C5HF4N-, the detachment rate at 303K was 520±180s-1. The attachment/detachment equilibrium yielded experimental electron affinities EA(C5F5N )=0.70±0.05eV and EA(2,3,5,6-C5HF4N )=0.40±0.08eV. Electronic structure calculations were carried out for these molecules and related C5HxF5-xN using density-functional theory and the G3(MP2)‖B3LYP compound method. The EAs are found to decrease by 0.25eV, on average, with each F substitution by H. The calculated EAs are in good agreement with the present experimental results.
López, Xavier; Bo, Carles; Poblet, Josep M
2002-10-23
A series of systematic DFT calculations were conducted on Keggin [SiW(9)M(3)O(40)](n-), M = Mo, V, and Nb; and Wells-Dawson anions [P(2)M(18)O(62)],(6-) M = W and Mo; [P(2)M(15)M(3)'O(62)](m-), M = W and Mo, M' = W, Mo, and V to analyze the redox properties and the basicity of the external oxygen sites in polyoxometalates with nonequivalent addenda metals. The energy and composition of the lowest unoccupied orbitals, formally delocalized over the addenda atoms, determine the redox properties of a polyoxometalate. When a Mo(6+) substitutes one W(6+) in the 1:12 tungstate, the energy of the LUMO decreases and the cluster is more easily reduced. The tungstoniobates behave differently because the niobium orbitals insert into the tungsten band and the reduction of [SiW(9)Nb(3)O(40)](7-) yields the blue species SiW(9)Nb(3) 1e and not the cluster SiW(9)Nb(2)Nb(IV). In Wells-Dawson structures, the polar and equatorial sites have different electron affinities and the reduction preferentially occurs in the equatorial sites. Inserting ions with larger electron affinities into the polar sites can modify this traditional conduct. Hence, the trisubstituted [P(2)W(15)V(3)O(62)](9-) anion is reduced in the vanadium polar sites. By means of molecular electrostatic potential maps and the relative energy of the various protonated forms of [SiW(9)V(3)O(40)](7-) and [SiW(9)Mo(3)O(40)](4-), we established the basicity scale: OV(2) > OMo(2) > OW(2) > OV > OW > OMo. Finally, a continuum model for the solvent enabled us to compare anions with different total charges.
Fast Electron Beam Simulation and Dose Calculation
Trindade, A; Peralta, L; Lopes, M C; Alves, C; Chaves, A
2003-01-01
A flexible multiple source model capable of fast reconstruction of clinical electron beams is presented in this paper. A source model considers multiple virtual sources emulating the effect of accelerator head components. A reference configuration (10 MeV and 10x10 cm2 field size) for a Siemens KD2 linear accelerator was simulated in full detail using GEANT3 Monte Carlo code. Our model allows the reconstruction of other beam energies and field sizes as well as other beam configurations for similar accelerators using only the reference beam data. Electron dose calculations were performed with the reconstructed beams in a water phantom and compared with experimental data. An agreement of 1-2% / 1-2 mm was obtained, equivalent to the accuracy of full Monte Carlo accelerator simulation. The source model reduces accelerator simulation CPU time by a factor of 7500 relative to full Monte Carlo approaches. The developed model was then interfaced with DPM, a fast radiation transport Monte Carlo code for dose calculati...
Coe, J P; Paterson, M J
2013-01-01
The method of Monte Carlo configuration interaction (MCCI) [1,2] is applied to the calculation of multipole moments. We look at the ground and excited state dipole moments in carbon monoxide. We then consider the dipole of NO, the quadrupole of the nitrogen molecule and of BH. An octupole of methane is also calculated. We consider experimental geometries and also stretched bonds. We show that these non-variational quantities may be found to relatively good accuracy when compared with FCI results, yet using only a small fraction of the full configuration interaction space. MCCI results in the aug-cc-pVDZ basis are seen to generally have reasonably good agreement with experiment. We also investigate the performance of MCCI when applied to ionisation energies and electron affinities of atoms in an aug-cc-pVQZ basis. We compare the MCCI results with full configuration-interaction quantum Monte Carlo [3,4] and `exact' non-relativistic results [3,4]. We show that MCCI could be a useful alternative for the calculati...
Asfandiarov, N. L.; Pshenichnyuk, S. A.; Vorob'ev, A. S.; Nafikova, E. P.; Mavrodiev, V. K.; Furlei, I. I.; Dokichev, V. A.; Platonov, D. N.; Belyy, A. Yu.
2017-05-01
Cycloheptatriene derivatives are studied by means of resonance electron capture negative ion mass spectrometry (REC NIMS). The average lifetimes of molecular negative ions (NIs) are measured with respect to electron autodetachment. Using the Arrhenius approach, electron affinity EAa of the molecules under study is estimated, and the effective temperature of the resulting negative molecular ions is determined as a function of the electron energy. It is assumed that the dissociation of negative molecular ions in the ground electronic state is a process similar to that of the thermal degradation of molecules.
DEFF Research Database (Denmark)
Dahlstrand, Christian; Yamazaki, Kaoru; Kilså, Kristine
2010-01-01
The extent of substituent influence on the vertical electron affinities (EAs) and ionization energies (IEs) of 43 substituted tria-, penta-, and heptafulvenes was examined computationally at the OVGF/6-311G(d)//B3LYP/6-311G(d) level of theory and compared with those of tetracyanoquinodimethane...... of the EAs and IEs were rationalized by qualitative arguments based on frontier orbital symmetries for the different fulvene classes with either X or Y being constant. The minimum and maximum values found for the calculated EAs of the tria-, penta-, and heptafulvenes were 0.51-2.05, 0.24-3.63, and 0...
Parthiban, S.; Martin, Jan M. L.
2001-01-01
The performance of two recent {\\em ab initio} computational thermochemistry schemes, W1 and W2 theory [J.M.L. Martin and G. de Oliveira, J. Chem. Phys. 111, 1843 (1999}], is assessed for an enlarged sample of thermochemical data consisting of the ionization potentials and electron affinities in the G2-1 and G2-2 sets, as well as the heats of formation in the G2-1 and a subset of the G2-2 set. We find W1 theory to be several times more accurate for ionization potentials and electron affinities...
Simulated electron affinity tuning in metal-insulator-metal (MIM) diodes
Mistry, Kissan; Yavuz, Mustafa; Musselman, Kevin P.
2017-05-01
Metal-insulator-metal diodes for rectification applications must exhibit high asymmetry, nonlinearity, and responsivity. Traditional methods of improving these figures of merit have consisted of increasing insulator thickness, adding multiple insulator layers, and utilizing a variety of metal contact combinations. However, these methods have come with the price of increasing the diode resistance and ultimately limiting the operating frequency to well below the terahertz regime. In this work, an Airy Function Transfer Matrix simulation method was used to observe the effect of tuning the electron affinity of the insulator as a technique to decrease the diode resistance. It was shown that a small increase in electron affinity can result in a resistance decrease in upwards of five orders of magnitude, corresponding to an increase in operating frequency on the same order. Electron affinity tuning has a minimal effect on the diode figures of merit, where asymmetry improves or remains unaffected and slight decreases in nonlinearity and responsivity are likely to be greatly outweighed by the improved operating frequency of the diode.
Influence of metallic surface states on electron affinity of epitaxial AlN films
Energy Technology Data Exchange (ETDEWEB)
Mishra, Monu; Krishna, Shibin; Aggarwal, Neha [Advanced Materials and Devices Division, CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi110012 (India); Academy of Scientific and Innovative Research (AcSIR), CSIR-NPL Campus, Dr. K.S. Krishnan Marg, New Delhi 110012 (India); Gupta, Govind, E-mail: govind@nplindia.org [Advanced Materials and Devices Division, CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi110012 (India); Academy of Scientific and Innovative Research (AcSIR), CSIR-NPL Campus, Dr. K.S. Krishnan Marg, New Delhi 110012 (India)
2017-06-15
The present article investigates surface metallic states induced alteration in the electron affinity of epitaxial AlN films. AlN films grown by plasma-assisted molecular beam epitaxy system with (30% and 16%) and without metallic aluminium on the surface were probed via photoemission spectroscopic measurements. An in-depth analysis exploring the influence of metallic aluminium and native oxide on the electronic structure of the films is performed. It was observed that the metallic states pinned the Fermi Level (FL) near valence band edge and lead to the reduction of electron affinity (EA). These metallic states initiated charge transfer and induced changes in surface and interface dipoles strength. Therefore, the EA of the films varied between 0.6–1.0 eV due to the variation in contribution of metallic states and native oxide. However, the surface barrier height (SBH) increased (4.2–3.5 eV) adversely due to the availability of donor-like surface states in metallic aluminium rich films.
Ab initio MCDHF calculations of electron-nucleus interactions
Bieroń, Jacek; Froese Fischer, Charlotte; Fritzsche, Stephan; Gaigalas, Gediminas; Grant, Ian P.; Indelicato, Paul; Jönsson, Per; Pyykkö, Pekka
2015-05-01
We present recent advances in the development of atomic ab initio multiconfiguration Dirac-Hartree-Fock theory, implemented in the GRASP relativistic atomic structure code. For neutral atoms, the deviations of properties calculated within the Dirac-Hartree-Fock (DHF) method (based on independent particle model of an atomic cloud) are usually dominated by electron correlation effects, i.e. the non-central interactions of individual electrons. We present the recent advances in accurate calculations of electron correlation effects in small, medium, and heavy neutral atoms. We describe methods of systematic development of multiconfiguration expansions leading to systematic, controlled improvement of the accuracy of the ab initio calculations. These methods originate from the concept of the complete active space (CAS) model within the DHF theory, which, at least in principle, permits fully relativistic calculations with full account of electron correlation effects. The calculations within the CAS model on currently available computer systems are feasible only for very light systems. For heavier atoms or ions with more than a few electrons, restrictions have to be imposed on the multiconfiguration expansions. We present methods and tools, which are designed to extend the numerical calculations in a controlled manner, where multiconfiguration expansions account for all leading electron correlation effects. We show examples of applications of the GRASP code to calculations of hyperfine structure constants, but the code may be used for calculations of arbitrary bound-state atomic properties. In recent years it has been applied to calculations of atomic and ionic spectra (transition energies and rates), to determinations of nuclear electromagnetic moments, as well as to calculations related to interactions of bound electrons with nuclear electromagnetic moments leading to violations of discrete symmetries.
First-principles electronic-band calculations on organic conductors
Directory of Open Access Journals (Sweden)
Shoji Ishibashi
2009-01-01
Full Text Available Predicting electronic-band structures is a key issue in understanding the properties of materials or in materials design. In this review article, application examples of first-principles calculations, which are not based on adjustable empirical parameters, to study electronic structures of organic conductors are described.
Zhao, Yi; Xu, Wenguo; Li, Qianshu; Xie, Yaoming; Schaefer, Henry F
2004-05-01
The molecular structures, electron affinities, and dissociation energies of the As(n)/As(-) (n) (n = 1-5) species have been examined using six density functional theory (DFT) methods. The basis set used in this work is of double-zeta plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated (Chem Rev 2002, 102, 231) for the prediction of electron affinities. The geometries are fully optimized with each DFT method independently. Three different types of the neutral-anion energy separations reported in this work are the adiabatic electron affinity (EA(ad)), the vertical electron affinity (EA(vert)), and the vertical detachment energy (VDE). The first dissociation energies D(e)(As(n-1)-As) for the neutral As(n) species, as well as those D(e)(As(-) (n-1)-As) and D(e) (As(n-1)-As(-)) for the anionic As(-) (n) species, have also been reported. The most reliable adiabatic electron affinities, obtained at the DZP++ BLYP level of theory, are 0.90 (As), 0.74 (As(2)), 1.30 (As(3)), 0.49 (As(4)), and 3.03 eV (As(5)), respectively. These EA(ad) values for As, As(2), and As(4) are in good agreement with experiment (average absolute error 0.09 eV), but that for As(3) is a bit smaller than the experimental value (1.45 +/- 0.03 eV). The first dissociation energies for the neutral arsenic clusters predicted by the B3LYP method are 3.93 eV (As(2)), 2.04 eV (As(3)), 3.88 eV (As(4)), and 1.49 eV (As(5)). Compared with the available experimental dissociation energies for the neutral clusters, the theoretical predictions are excellent. Two dissociation limits are possible for the arsenic cluster anions. The atomic arsenic results are 3.91 eV (As(-) (2) --> As(-) + As), 2.46 eV (As(-) (3) --> As(-) (2) + As), 3.14 eV (As(-) (4) --> As(-) (3) + As), and 4.01 eV (As(-) (5) --> As(-) (4) + As). For dissociation to neutral arsenic clusters, the predicted dissociation energies are 2.43 eV (As(-) (3) --> As(2) + As
Calculations of skyshine from an intense portable electron linac
Energy Technology Data Exchange (ETDEWEB)
Estes, G.P.; Hughes, H.G.; Fry, D.A.; Haynie, J.S. [Los Alamos National Lab., NM (United States); Shaughnessy, C.H.
1994-12-31
The MCNP Monte carlo code has been used at Los Alamos to calculate skyshine and terrain albedo efects from an intense portable electron linear accelerator that is to be used by the Russian Federation to radiograph nuclear weapons that may have been damaged by accidents. Relative dose rate profiles have been calculated. The design of the accelerator, along with a diagram, is presented.
Electronic band-structure calculations of some magnetic chromium compounds
VANBRUGGEN, CF; HAAS, C; DEGROOT, RA
1989-01-01
In this paper band-structure calculations of CrS, CrSe, Cr3Se4 and CrSb are presented. Together with our accompanying results for the chromium tellurides, these calculations give a coherent picture of the changes in the electronic structure caused by anion substitution and by introduction of cation
Rodionov, A. A.; Golyashov, V. A.; Chistokhin, I. B.; Jaroshevich, A. S.; Derebezov, I. A.; Haisler, V. A.; Shamirzaev, T. S.; Marakhovka, I. I.; Kopotilov, A. V.; Kislykh, N. V.; Mironov, A. V.; Aksenov, V. V.; Tereshchenko, O. E.
2017-09-01
The photoemission and injection properties of two GaAs/(Al,Ga)As electrodes with effective negative electron affinity (NEA) are studied in the parallel-plate capacitorlike vacuum photodiode. Both electrodes are bonded to the glass of the input windows, allowing measuring the quantum yield in the transmission and reflection modes. The photodiode with NEA states of both electrodes is sensitive to the illumination in the 400-900 nm range and produces the photocurrent with no bias applied between electrodes. The energy distribution of emitted electrons is studied as a function of the transverse energy component to the surface in the temperature range of 20-300 K. The presence of the fine structure in the photoemission spectra is associated with the electron-phonon coupling in two-dimensional quantized states in the band-bending region. The two-electrode vacuum photoemission system demonstrates the negative differential conductivity. The cathodoluminescence signal is measured as a function of free-electron injection energy with the threshold appearance less than 0.05 V between electrodes.
Determination of the electron affinity of astatine and polonium by laser photodetachment
We propose to conduct the first electron affinity (EA) measurements of the two elements astatine (At) and polonium (Po). Collinear photo-detachment spectroscopy will allow us to measure these quantities with an uncertainty limited only by the spectral line width of the laser. We plan to use negative ion beams of the two radioactive elements At and Po, which are only accessible on-line and at ISOLDE. The feasibility of our proposed method and the functionality of the experimental setup have been demonstrated at ISOLDE in off-line tests by the clear observation of the photo-detachment threshold for stable iodine. This proposal is based on our Letter of Intent I-148.
Capturing enveloped viruses on affinity grids for downstream cryo-electron microscopy applications.
Kiss, Gabriella; Chen, Xuemin; Brindley, Melinda A; Campbell, Patricia; Afonso, Claudio L; Ke, Zunlong; Holl, Jens M; Guerrero-Ferreira, Ricardo C; Byrd-Leotis, Lauren A; Steel, John; Steinhauer, David A; Plemper, Richard K; Kelly, Deborah F; Spearman, Paul W; Wright, Elizabeth R
2014-02-01
Electron microscopy (EM), cryo-electron microscopy (cryo-EM), and cryo-electron tomography (cryo-ET) are essential techniques used for characterizing basic virus morphology and determining the three-dimensional structure of viruses. Enveloped viruses, which contain an outer lipoprotein coat, constitute the largest group of pathogenic viruses to humans. The purification of enveloped viruses from cell culture presents certain challenges. Specifically, the inclusion of host-membrane-derived vesicles, the complete destruction of the viruses, and the disruption of the internal architecture of individual virus particles. Here, we present a strategy for capturing enveloped viruses on affinity grids (AG) for use in both conventional EM and cryo-EM/ET applications. We examined the utility of AG for the selective capture of human immunodeficiency virus virus-like particles, influenza A, and measles virus. We applied nickel-nitrilotriacetic acid lipid layers in combination with molecular adaptors to selectively adhere the viruses to the AG surface. This further development of the AG method may prove essential for the gentle and selective purification of enveloped viruses directly onto EM grids for ultrastructural analyses.
Electronic structure of crystalline uranium nitride: LCAO DFT calculations
Energy Technology Data Exchange (ETDEWEB)
Evarestov, R.A.; Losev, M.V.; Panin, A.I. [Department of Quantum Chemistry, St. Petersburg State University, 26 University Prospekt, Stary Peterghof, 198504 (Russian Federation); Mosyagin, N.S. [Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg District, 188300 (Russian Federation); Titov, A.V. [Department of Quantum Chemistry, St. Petersburg State University, 26 University Prospekt, Stary Peterghof, 198504 (Russian Federation); Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg District, 188300 (Russian Federation)
2008-01-15
The results of the first LCAO DFT calculations of cohesive energy, band structure and charge distribution in uranium nitride (UN) crystal are presented and discussed. The calculations are made with the uranium atom relativistic effective core potentials, including 60, 78 and 81 electrons in the core. It is demonstrated that the chemical bonding in UN crystal has a metallic-covalent nature. Three 5f-electrons are localized on the U atom and occupy the states near the Fermi level. The metallic nature of the crystal is due to the f-character of both the valence-band top and the conduction-band bottom. The covalent bonds are formed by the interaction of 7s- and 6d-states of the uranium atom with the 2p-states of the nitrogen atom. It is shown that the inclusion of 5f-electrons in the atomic core introduces small changes in the calculated cohesive energy of UN crystal and electron charge distribution. However, the inclusion of 5s-, 5p-, 5d-electrons in the valence shell allows the better agreement with the calculated and experimental cohesive-energy value. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Multiconfiguration calculations of electronic isotope shift factors in Al I
Filippin, Livio; Ekman, Jörgen; Fritzsche, Stephan; Godefroid, Michel; Jönsson, Per
2016-01-01
The present work reports results from systematic multiconfiguration Dirac-Hartree-Fock calculations of electronic isotope shift factors for a set of transitions between low-lying states in neutral aluminium. These electronic quantities together with observed isotope shifts between different pairs of isotopes provide the changes in mean-square charge radii of the atomic nuclei. Two computational approaches are adopted for the estimation of the mass- and field shift factors. Within these approaches, different models for electron correlation are explored in a systematic way to determine a reliable computational strategy and estimate theoretical uncertainties of the isotope shift factors.
Calculations on the electronic excited states of ureas and oligoureas.
Oakley, Mark T; Guichard, Gilles; Hirst, Jonathan D
2007-03-29
We report CASPT2 calculations on the electronic excited states of several ureas. For monoureas, we find an electric dipole forbidden n --> pi* transition between 180 and 210 nm, dependent on the geometry and substituents of the urea. We find two intense pinb --> pi* transitions between 150 and 210 nm, which account for the absorptions seen in the experimental spectra. The n' --> pi* and pib --> pi* transitions are at wavelengths below 125 nm, which is below the lower limit of the experimental spectra. Parameter sets modeling the charge densities of the electronic transitions have been derived and permit calculations on larger oligoureas, using the exciton matrix method. For glycouril, a urea dimer, both the CASPT2 method and the matrix method yield similar results. Calculations of the electronic circular dichroism spectrum of an oligourea containing eight urea groups indicate that the experimental spectrum cannot be reproduced without the inclusion of electronic excitations involving the side chains. These calculations are one of the first attempts to understand the relationship between the structure and excited states of this class of macromolecule.
Three real-space discretization techniques in electronic structure calculations
Torsti, T; Eirola, T; Enkovaara, J; Hakala, T; Havu, P; Havu, [No Value; Hoynalanmaa, T; Ignatius, J; Lyly, M; Makkonen, [No Value; Rantala, TT; Ruokolainen, J; Ruotsalainen, K; Rasanen, E; Saarikoski, H; Puska, MJ
A characteristic feature of the state-of-the-art of real-space methods in electronic structure calculations is the diversity of the techniques used in the discretization of the relevant partial differential equations. In this context, the main approaches include finite-difference methods, various
Calculational aspects of electron-phonon coupling at surfaces
Energy Technology Data Exchange (ETDEWEB)
Nojima, Akihiro; Yamashita, Koichi [Department of Chemical System Engineering, School of Engineering, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656 (Japan); Hellsing, Bo [Department of Physics, Goeteborg University, Fysikgraend 3, S-412 96 Goeteborg (Sweden)], E-mail: nojima@tcl.t.u-tokyo.ac.jp
2008-06-04
We study the validity of two frequently used approximations in calculations of electron-phonon coupling at surfaces. The rigid-ion approximation is a standard approximation used for the bulk metals. On the basis of density functional theory calculations, we find that for Be this approximation is as valid for surface atoms as for bulk atoms. In addition, the slab method for calculations of a phonon induced surface state lifetime is examined. The convergence of the electron-phonon matrix element with respect to the thickness of the slab is studied for several systems. When the number of slab layers is increased, the net effect of decreasing overlap and increasing number of final states depends strongly on the decay length of the surface state wavefunction and the band structure.
Integral approximations in ab initio, electron propagator calculations.
Flores-Moreno, Roberto; Ortiz, J V
2009-09-28
Treatments of interelectronic repulsion that avoid four-center integrals have been incorporated in ab initio, electron-propagator calculations with diagonal self-energy matrices. Whereas the formal scaling of arithmetic operations in the propagator calculations is unaffected, the reduction of storage requirements is substantial. Moreover, the scaling of integral transformations to the molecular orbital base is lowered by one order. Four-index, electron-repulsion integrals are regenerated from three-index intermediates. Test calculations with widely applied self-energy approximations demonstrate the accuracy of this approach. Only small errors are introduced when this technique is used with quasiparticle virtual orbitals, provided that conventional techniques of integral evaluation are used in the construction of density-difference matrices.
Superposition dose calculation incorporating Monte Carlo generated electron track kernels.
Keall, P J; Hoban, P W
1996-04-01
The superposition/convolution method and the transport of pregenerated Monte Carlo electron track data have been combined into the Super-Monte Carlo (SMC) method, an accurate 3-D x-ray dose calculation algorithm. The primary dose (dose due to electrons ejected by primary photons) is calculated by transporting pregenerated (in water) Monte Carlo electron tracks from each primary photon interaction site, weighted by the terma for that site. The length of each electron step is scaled by the inverse of the density of the medium at the beginning of the step. Because the density scaling of the electron tracks is performed for each individual transport step, the limitations of the macroscopic scaling of kernels (in the superposition algorithm) are overcome. This time-consuming step-by-step transport is only performed for the primary dose calculation, where current superposition methods are most lacking. The scattered dose (dose due to electrons set in motion by scattered photons) is calculated by superposition. In both a water-lung-water phantom and a two lung-block phantom, SMC dose distributions are more consistent with Monte Carlo generated dose distributions than are superposition dose distributions, especially for small fields and high energies-for an 18-MV, 5 X 5-cm(2) beam, the central axis dose discrepancy from Monte Carlo is reduced from 4.5% using superposition to 1.5% using SMC. The computation time for this technique is approximately 2 h (depending on the simulation history), 20 times slower than superposition, but 15 times faster than a full Monte Carlo simulation (on our platform).
Calculating of Coupling Factor of Microwave Electron Gun
Bian, Xiaohao; Li, Derun; Zheng, Shuxin
2005-01-01
To design the coupler of a designing microwave electron gun, we use the "energy method" proposed by Derun Li, et al. The intrinsic Q of the electron gun cavity is very high: about 20000. The method calculates the intrinsic and external Q values of a cavity coupled to a waveguide using MAFIA code in time domain. The comparisons between simulation and experimental results are given for a set of different coupling iris apertures and height. The result shows that "energy method" works efficiently for high Q cavities.
Electron affinities of aromatic hydrocarbons and disproportionation of their radical-anions
Energy Technology Data Exchange (ETDEWEB)
Szwarc, M.
1986-09-01
Electron affinities of aromatic hydrocarbons measured in the gas-phase and in solutions are compared. The experimental methods used for their determination are briefly reviewed. The reduction yields the respective radical-anions. Radical-anions may undergo disproportionation, a reaction described by the scheme: 2A/sup -/ . , Cat/sup =/ in equilibrium A + A/sup 2-/, 2 Cat/sup +/, K/sub dipr/. The disproportionation constant, K/sub dipr/, is greatly affected by the nature of aromatic hydrocarbon, of the cation, and of the solvent. Variation of each of these factors is illustrated. Variation of the cation and solvent results in changes of the disproportionation constant as large as factors of 10/sup 25/. The causes of these variations are rationalized and discussed in terms of the respective ..delta..H and ..delta..S. Kinetics of disproportionation was investigated by flash-photolysis techniques. The experimental approach is described. The peculiarities of Ba salts deserved some discussion to clarify the nature of those salts. The effect of disproportionation on reactions of radical-anions are described: namely on cis-trans isomerization of stilbenes, on protonation of radical-anions of anthracene an perylene, on dissociation of radical anions of aromatic derivatives ethane, etc.
A modified dose calculation formalism for electronic brachytherapy sources.
DeWerd, Larry A; Culberson, Wesley S; Micka, John A; Simiele, Samantha J
2015-01-01
To propose a modification of the current dose calculation formalism introduced in the Task Group No. 43 Report (TG-43) to accommodate an air-kerma rate standard for electronic brachytherapy sources as an alternative to an air-kerma strength standard. Electronic brachytherapy sources are miniature x-ray tubes emitting low energies with high-dose-rates. The National Institute of Standards and Technology (NIST) has introduced a new primary air-kerma rate standard for one of these sources, in contrast to air-kerma strength. A modification of the TG-43 protocol for calculation of dose-rate distributions around electronic brachytherapy sources including sources in an applicator is presented. It cannot be assumed that the perturbations from sources in an applicator are negligible, and thus, the applicator is incorporated in the formalism. The modified protocol mimics the fundamental methodology of the original TG-43 formalism, but now incorporates the new NIST-traceable source strength metric of air-kerma rate at 50 cm and introduces a new subscript, i, to denote the presence of an applicator used in treatment delivery. Applications of electronic brachytherapy sources for surface brachytherapy are not addressed in this Technical Note since they are well documented in other publications. A modification of the AAPM TG-43 protocol has been developed to accommodate an air-kerma rate standard for electronic brachytherapy sources as an alternative to an air-kerma strength standard. The modified TG-43 formalism allows dose calculations to be performed using a new NIST-traceable source strength metric and introduces the concept of applicator-specific formalism parameters denoted with subscript, i. Copyright © 2015 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.
Quasiparticle GW calculations within the GPAW electronic structure code
DEFF Research Database (Denmark)
Hüser, Falco
are explained in detail and many examples are given. This provides a full understanding of how the code works and how the outcome should be interpreted. Secondly, it gives an extensive discussion of calculated results for the electronic structure of 3-dimensional, 2-dimensional and finite systems and comparison......The GPAW electronic structure code, developed at the physics department at the Technical University of Denmark, is used today by researchers all over the world to model the structural, electronic, optical and chemical properties of materials. They address fundamental questions in material science...... and use their knowledge to design new materials for a vast range of applications. Todays hottest topics are, amongst many others, better materials for energy conversion (e.g. solar cells), energy storage (batteries) and catalysts for the removal of environmentally dangerous exhausts. The mentioned...
Energy Technology Data Exchange (ETDEWEB)
Hoke, Eric T.; Sachs-Quintana, I.T.; Kauvar, Isaac; Mateker, William R.; Peters, Craig H.; McGehee, Michael D. [Department of Material Science and Engineering, Stanford University, 476 Lomita Mall, Stanford, CA 94305 (United States); Lloyd, Matthew T.; Nardes, Alexandre M.; Kopidakis, Nikos [National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401 (United States)
2012-11-15
Understanding the stability and degradation mechanisms of organic solar materials is critically important to achieving long device lifetimes. Here, an investigation of the photodegradation of polymer:fullerene blend films exposed to ambient conditions for a variety of polymer and fullerene derivative combinations is presented. Despite the wide range in polymer stabilities to photodegradation, the rate of irreversible polymer photobleaching in blend films is found to consistently and dramatically increase with decreasing electron affinity of the fullerene derivative. Furthermore, blends containing fullerenes with the smallest electron affinities photobleached at a faster rate than films of the pure polymer. These observations can be explained by a mechanism where both the polymer and fullerene donate photogenerated electrons to diatomic oxygen to form the superoxide radical anion which degrades the polymer. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
An efficient basis set representation for calculating electrons in molecules
Jones, Jeremiah R; Lawler, Keith V; Vecharynski, Eugene; Ibrahim, Khaled Z; Williams, Samuel; Abeln, Brant; Yang, Chao; Haxton, Daniel J; McCurdy, C William; Li, Xiaoye S; Rescigno, Thomas N
2015-01-01
The method of McCurdy, Baertschy, and Rescigno, J. Phys. B, 37, R137 (2004) is generalized to obtain a straightforward, surprisingly accurate, and scalable numerical representation for calculating the electronic wave functions of molecules. It uses a basis set of product sinc functions arrayed on a Cartesian grid, and yields 1 kcal/mol precision for valence transition energies with a grid resolution of approximately 0.1 bohr. The Coulomb matrix elements are replaced with matrix elements obtained from the kinetic energy operator. A resolution-of-the-identity approximation renders the primitive one- and two-electron matrix elements diagonal; in other words, the Coulomb operator is local with respect to the grid indices. The calculation of contracted two-electron matrix elements among orbitals requires only O(N log(N)) multiplication operations, not O(N^4), where N is the number of basis functions; N = n^3 on cubic grids. The representation not only is numerically expedient, but also produces energies and proper...
R-matrix calculations of electron impact electronic excitation of BeH
Darby-Lewis, Daniel; Mašín, Zdeněk; Tennyson, Jonathan
2017-09-01
The R-matrix method is used to perform high-level calculations of electron collisions with beryllium mono-hydride at its equilibrium geometry with a particular emphasis on electron impact electronic excitation. Several target and scattering models are considered. The calculations were performed using (1) the UKRMol suite which relies on the use of Gaussian type orbitals (GTOs) to represent the continuum and (2) using the new UKRMol+ suite which allows the inclusion of B-spline type orbitals in the basis for the continuum. The final close-coupling scattering models used the UKRMol+ code and a frozen core, valence full configuration interaction, method based on a diffuse GTO atomic basis set. The calculated electronic properties of the molecule are in very good agreement with state-of-the-art electronic structure calculations. The use of the UKRMol+ suite proved critical since it allowed the use of a large R-matrix sphere (35 Bohr), necessary to contain the diffuse electronic states of the molecule. The corresponding calculations using UKRMol are not possible due to numerical problems associated with the combination of GTO-only continuum and a large R-matrix sphere. This work provides the first demonstration of the utility and numerical stability of the new UKRMol+ code. The inelastic cross sections obtained here present a significant improvement over the results of earlier studies on BeH.
Radial Moment Calculations of Coupled Electron-Photon Beams
Energy Technology Data Exchange (ETDEWEB)
FRANKE,BRIAN C.; LARSEN,EDWARD W.
2000-07-19
The authors consider the steady-state transport of normally incident pencil beams of radiation in slabs of material. A method has been developed for determining the exact radial moments of 3-D beams of radiation as a function of depth into the slab, by solving systems of 1-D transport equations. They implement these radial moment equations in the ONEBFP discrete ordinates code and simulate energy-dependent, coupled electron-photon beams using CEPXS-generated cross sections. Modified P{sub N} synthetic acceleration is employed to speed up the iterative convergence of the 1-D charged particle calculations. For high-energy photon beams, a hybrid Monte Carlo/discrete ordinates method is examined. They demonstrate the efficiency of the calculations and make comparisons with 3-D Monte Carlo calculations. Thus, by solving 1-D transport equations, they obtain realistic multidimensional information concerning the broadening of electron-photon beams. This information is relevant to fields such as industrial radiography, medical imaging, radiation oncology, particle accelerators, and lasers.
Cao, Ying; Zhang, Song-Chen; Zhang, Min; Shen, Guang-Bin; Zhu, Xiao-Qing
2013-07-19
A series of 69 polar olefins with various typical structures (X) were synthesized and the thermodynamic affinities (defined in terms of the molar enthalpy changes or the standard redox potentials in this work) of the polar olefins obtaining hydride anions, hydrogen atoms, and electrons, the thermodynamic affinities of the radical anions of the polar olefins (X(•-)) obtaining protons and hydrogen atoms, and the thermodynamic affinities of the hydrogen adducts of the polar olefins (XH(•)) obtaining electrons in acetonitrile were determined using titration calorimetry and electrochemical methods. The pure C═C π-bond heterolytic and homolytic dissociation energies of the polar olefins (X) in acetonitrile and the pure C═C π-bond homolytic dissociation energies of the radical anions of the polar olefins (X(•-)) in acetonitrile were estimated. The remote substituent effects on the six thermodynamic affinities of the polar olefins and their related reaction intermediates were examined using the Hammett linear free-energy relationships; the results show that the Hammett linear free-energy relationships all hold in the six chemical and electrochemical processes. The information disclosed in this work could not only supply a gap of the chemical thermodynamics of olefins as one class of very important organic unsaturated compounds but also strongly promote the fast development of the chemistry and applications of olefins.
Relativistic collision rate calculations for electron-air interactions
Energy Technology Data Exchange (ETDEWEB)
Graham, G. [EG and G Energy Measurements, Inc., Los Alamos, NM (United States); Roussel-Dupre, R. [Los Alamos National Lab., NM (United States)
1993-12-01
The most recent data available on differential cross sections for electron-air interactions are used to calculate the avalanche, momentum transfer, and energy loss rates that enter into the fluid equations. Data for the important elastic, inelastic, and ionizing processes are generally available out to electron energies of 1--10 keV. Prescriptions for extending these cross sections to the relativistic regime are presented. The angular dependence of the cross sections is included where data are available as is the doubly differential cross section for ionizing collisions. The collision rates are computed by taking moments of the Boltzmann collision integrals with the assumption that the electron momentum distribution function is given by the Juettner distribution function which satisfies the relativistic H- theorem and which reduces to the familiar Maxwellian velocity distribution in the nonrelativistic regime. The distribution function is parameterized in terms of the electron density, mean momentum, and thermal energy and the rates are therefore computed on a two dimensional grid as a function of mean kinetic energy and thermal energy.
Efficient evaluation of atom tunneling combined with electronic structure calculations
Ásgeirsson, Vilhjálmur; Arnaldsson, Andri; Jónsson, Hannes
2018-03-01
Methodology for finding optimal tunneling paths and evaluating tunneling rates for atomic rearrangements is described. First, an optimal JWKB tunneling path for a system with fixed energy is obtained using a line integral extension of the nudged elastic band method. Then, a calculation of the dynamics along the path is used to determine the temperature at which it corresponds to an optimal Feynman path for thermally activated tunneling (instanton) and a harmonic approximation is used to estimate the transition rate. The method is illustrated with calculations for a modified two-dimensional Müller-Brown surface but is efficient enough to be used in combination with electronic structure calculations of the energy and atomic forces in systems containing many atoms. An example is presented where tunneling is the dominant mechanism well above room temperature as an H3BNH3 molecule dissociates to form H2. Also, a solid-state example is presented where density functional theory calculations of H atom tunneling in a Ta crystal give close agreement with experimental measurements on hydrogen diffusion over a wide range in temperature.
An electronic application for rapidly calculating Charlson comorbidity score
Directory of Open Access Journals (Sweden)
Jani Ashesh B
2004-12-01
Full Text Available Abstract Background Uncertainty regarding comorbid illness, and ability to tolerate aggressive therapy has led to minimal enrollment of elderly cancer patients into clinical trials and often substandard treatment. Increasingly, comorbid illness scales have proven useful in identifying subgroups of elderly patients who are more likely to tolerate and benefit from aggressive therapy. Unfortunately, the use of such scales has yet to be widely integrated into either clinical practice or clinical trials research. Methods This article reviews evidence for the validity of the Charlson Comorbidity Index (CCI in oncology and provides a Microsoft Excel (MS Excel Macro for the rapid and accurate calculation of CCI score. The interaction of comorbidity and malignant disease and the validation of the Charlson Index in oncology are discussed. Results The CCI score is based on one year mortality data from internal medicine patients admitted to an inpatient setting and is the most widely used comorbidity index in oncology. An MS Excel Macro file was constructed for calculating the CCI score using Microsoft Visual Basic. The Macro is provided for download and dissemination. The CCI has been widely used and validated throughout the oncology literature and has demonstrated utility for most major cancers. The MS Excel CCI Macro provides a rapid method for calculating CCI score with or without age adjustments. The calculator removes difficulty in score calculation as a limitation for integration of the CCI into clinical research. The simple nature of the MS Excel CCI Macro and the CCI itself makes it ideal for integration into emerging electronic medical records systems. Conclusions The increasing elderly population and concurrent increase in oncologic disease has made understanding the interaction between age and comorbid illness on life expectancy increasingly important. The MS Excel CCI Macro provides a means of increasing the use of the CCI scale in clinical
Multi-million atom electronic structure calculations for quantum dots
Usman, Muhammad
Quantum dots grown by self-assembly process are typically constructed by 50,000 to 5,000,000 structural atoms which confine a small, countable number of extra electrons or holes in a space that is comparable in size to the electron wavelength. Under such conditions quantum dots can be interpreted as artificial atoms with the potential to be custom tailored to new functionality. In the past decade or so, these nanostructures have attracted significant experimental and theoretical attention in the field of nanoscience. The new and tunable optical and electrical properties of these artificial atoms have been proposed in a variety of different fields, for example in communication and computing systems, medical and quantum computing applications. Predictive and quantitative modeling and simulation of these structures can help to narrow down the vast design space to a range that is experimentally affordable and move this part of nanoscience to nano-Technology. Modeling of such quantum dots pose a formidable challenge to theoretical physicists because: (1) Strain originating from the lattice mismatch of the materials penetrates deep inside the buffer surrounding the quantum dots and require large scale (multi-million atom) simulations to correctly capture its effect on the electronic structure, (2) The interface roughness, the alloy randomness, and the atomistic granularity require the calculation of electronic structure at the atomistic scale. Most of the current or past theoretical calculations are based on continuum approach such as effective mass approximation or k.p modeling capturing either no or one of the above mentioned effects, thus missing some of the essential physics. The Objectives of this thesis are: (1) to model and simulate the experimental quantum dot topologies at the atomistic scale; (2) to theoretically explore the essential physics i.e. long range strain, linear and quadratic piezoelectricity, interband optical transition strengths, quantum confined
Calculation of Electron Beam Potential Energy from RF Photocathode Gun
Liu Wan Ming; Power, John G; Wang, Haitao
2005-01-01
In this paper, we consider the contribution of potential energy to beam dynamics as simulated by PARMELA at low energies (10 - 30MeV). We have developed a routine to calculate the potential energy of the relativistic electron beam using the static coulomb potential in the rest frame (first order approximation as in PARMELA). We found that the potential energy contribution to the beam dynamics could be very significant, particularly with high charge beams generated by an RF photocathode gun. Our results show that when the potential energy is counted correctly and added to the kinetic energy from PARMELA, the total energy is conserved. Simulation results of potential and kinetic energies for short beams (~1 mm) at various charges (1 - 100 nC) generated by a high current RF photocathode gun are presented.
Chen, Edward S; Chen, Edward C M
2017-10-29
The anion mass spectral lifetimes for several aromatic hydrocarbons reported in the subject article were related to significantly different electron affinities. The different values are rationalized using negative ion mass spectral data. Electron affinities for polycyclic aromatic hydrocarbons are reported from the temperature dependence of unpublished electron capture detector data. These are compared with published values and the largest values are assigned to the ground state. The ground state adiabatic electron affinities: (eV) pentacene, 1.41(3); tetracene, 1.058(5); benz(a)pyrene, 0.82(4); benz(a) anthracene, 0.69(2) anthracene, 0.68(2); and pyrene, 0.59(1) are used to assign excited state adiabatic electron affinities: (eV) tetracene: 0.88(4); anthracene 0.53(1) ; pyrene, 0.41(1); benz(a)anthracene, 0.39(10); chrysene, 0.32(1); and phenanthrene, 0.12(2) and ground state adiabatic electron affinities: (eV) dibenz(a,j)anthracene, 0.69(2); dibenz(a,h)anthracene, 0.68(2); benz(e)pyrene, 0.60(2); and picene, 0.59(2) from experimental data. The lifetime of benz(a)pyrene is predicted to be larger than 150 μsec and for picene about 40 μsec, from ground state adiabatic electron affinities. The assignments of adiabatic electron affinities of aromatic hydrocarbons determined from electron capture detector and mass spectrometric data to ground and excited states are supported by constant electronegativities. A set of consistent ground state adiabatic electron affinities for fifteen polycyclic aromatic hydrocarbons is related to lifetimes from the subject article. This article is protected by copyright. All rights reserved.
Adaptations in Electronic Structure Calculations in Heterogeneous Environments
Energy Technology Data Exchange (ETDEWEB)
Talamudupula, Sai [Iowa State Univ., Ames, IA (United States)
2011-01-01
Modern quantum chemistry deals with electronic structure calculations of unprecedented complexity and accuracy. They demand full power of high-performance computing and must be in tune with the given architecture for superior e ciency. To make such applications resourceaware, it is desirable to enable their static and dynamic adaptations using some external software (middleware), which may monitor both system availability and application needs, rather than mix science with system-related calls inside the application. The present work investigates scienti c application interlinking with middleware based on the example of the computational chemistry package GAMESS and middleware NICAN. The existing synchronous model is limited by the possible delays due to the middleware processing time under the sustainable runtime system conditions. Proposed asynchronous and hybrid models aim at overcoming this limitation. When linked with NICAN, the fragment molecular orbital (FMO) method is capable of adapting statically and dynamically its fragment scheduling policy based on the computing platform conditions. Signi cant execution time and throughput gains have been obtained due to such static adaptations when the compute nodes have very di erent core counts. Dynamic adaptations are based on the main memory availability at run time. NICAN prompts FMO to postpone scheduling certain fragments, if there is not enough memory for their immediate execution. Hence, FMO may be able to complete the calculations whereas without such adaptations it aborts.
Richard, Ryan M.
2016-01-05
© 2016 American Chemical Society. In designing organic materials for electronics applications, particularly for organic photovoltaics (OPV), the ionization potential (IP) of the donor and the electron affinity (EA) of the acceptor play key roles. This makes OPV design an appealing application for computational chemistry since IPs and EAs are readily calculable from most electronic structure methods. Unfortunately reliable, high-accuracy wave function methods, such as coupled cluster theory with single, double, and perturbative triples [CCSD(T)] in the complete basis set (CBS) limit are too expensive for routine applications to this problem for any but the smallest of systems. One solution is to calibrate approximate, less computationally expensive methods against a database of high-accuracy IP/EA values; however, to our knowledge, no such database exists for systems related to OPV design. The present work is the first of a multipart study whose overarching goal is to determine which computational methods can be used to reliably compute IPs and EAs of electron acceptors. This part introduces a database of 24 known organic electron acceptors and provides high-accuracy vertical IP and EA values expected to be within ±0.03 eV of the true non-relativistic, vertical CCSD(T)/CBS limit. Convergence of IP and EA values toward the CBS limit is studied systematically for the Hartree-Fock, MP2 correlation, and beyond-MP2 coupled cluster contributions to the focal point estimates.
Żywicka, B.; Możejko, P.
2013-10-01
Cross section for electron impact ionization of carboplatin, C6H12N2O4Pt, and oxaliplatin, C8H14N2O4Pt, have been calculated within binary-encounter-Bethe model for energies from the ionization threshold up to 5000 eV. Cross section for elastic electron scattering from carboplatin and oxaliplatin molecules have also been derived using independent atom method (IAM) and additivity rule for collision energies ranging from 50 eV to 3000 eV. Obtained cross sections have been compared with relevant cross sections for cisplatin molecules.
Considerations of beta and electron transport in internal dose calculations
Energy Technology Data Exchange (ETDEWEB)
Bolch, W.E.; Poston, J.W. Sr. (Texas A and M Univ., College Station, TX (USA). Dept. of Nuclear Engineering)
1990-12-01
Ionizing radiation has broad uses in modern science and medicine. These uses often require the calculation of energy deposition in the irradiated media and, usually, the medium of interest is the human body. Energy deposition from radioactive sources within the human body and the effects of such deposition are considered in the field of internal dosimetry. In July of 1988, a three-year research project was initiated by the Nuclear Engineering Department at Texas A M University under the sponsorship of the US Department of Energy. The main thrust of the research was to consider, for the first time, the detailed spatial transport of electron and beta particles in the estimation of average organ doses under the Medical Internal Radiation Dose (MIRD) schema. At the present time (December of 1990), research activities are continuing within five areas. Several are new initiatives begun within the second or third year of the current contract period. They include: (1) development of small-scale dosimetry; (2) development of a differential volume phantom; (3) development of a dosimetric bone model; (4) assessment of the new ICRP lung model; and (5) studies into the mechanisms of DNA damage. A progress report is given for each of these tasks within the Comprehensive Report. In each use, preliminary results are very encouraging and plans for further research are detailed within this document. 22 refs., 13 figs., 1 tab.
Considerations of beta and electron transport in internal dose calculations
Energy Technology Data Exchange (ETDEWEB)
Bolch, W.E.; Poston, J.W. Sr.
1990-12-01
Ionizing radiation has broad uses in modern science and medicine. These uses often require the calculation of energy deposition in the irradiated media and, usually, the medium of interest is the human body. Energy deposition from radioactive sources within the human body and the effects of such deposition are considered in the field of internal dosimetry. In July of 1988, a three-year research project was initiated by the Nuclear Engineering Department at Texas A M University under the sponsorship of the US Department of Energy. The main thrust of the research was to consider, for the first time, the detailed spatial transport of electron and beta particles in the estimation of average organ doses under the Medical Internal Radiation Dose (MIRD) schema. At the present time (December of 1990), research activities are continuing within five areas. Several are new initiatives begun within the second or third year of the current contract period. They include: (1) development of small-scale dosimetry; (2) development of a differential volume phantom; (3) development of a dosimetric bone model; (4) assessment of the new ICRP lung model; and (5) studies into the mechanisms of DNA damage. A progress report is given for each of these tasks within the Comprehensive Report. In each case, preliminary results are very encouraging and plans for further research are detailed within this document.
Cholesky decomposition of the two-electron integral matrix in electronic structure calculations.
Røeggen, I; Johansen, Tor
2008-05-21
A standard Cholesky decomposition of the two-electron integral matrix leads to integral tables which have a huge number of very small elements. By neglecting these small elements, it is demonstrated that the recursive part of the Cholesky algorithm is no longer a bottleneck in the procedure. It is shown that a very efficient algorithm can be constructed when family type basis sets are adopted. For subsequent calculations, it is argued that two-electron integrals represented by Cholesky integral tables have the same potential for simplifications as density fitting. Compared to density fitting, a Cholesky decomposition of the two-electron matrix is not subjected to the problem of defining an auxiliary basis for obtaining a fixed accuracy in a calculation since the accuracy simply derives from the choice of a threshold for the decomposition procedure. A particularly robust algorithm for solving the restricted Hartree-Fock (RHF) equations can be speeded up if one has access to an ordered set of integral tables. In a test calculation on a linear chain of beryllium atoms, the advocated RHF algorithm nicely converged, but where the standard direct inversion in iterative space method converged very slowly to an excited state.
Yu, Guimei; Vago, Frank; Zhang, Dongsheng; Snyder, Jonathan E; Yan, Rui; Zhang, Ci; Benjamin, Christopher; Jiang, Xi; Kuhn, Richard J; Serwer, Philip; Thompson, David H; Jiang, Wen
2014-07-01
Single particle cryo-electron microscopy (cryo-EM) is an emerging powerful tool for structural studies of macromolecular assemblies (i.e., protein complexes and viruses). Although single particle cryo-EM requires less concentrated and smaller amounts of samples than X-ray crystallography, it remains challenging to study specimens that are low-abundance, low-yield, or short-lived. The recent development of affinity grid techniques can potentially further extend single particle cryo-EM to these challenging samples by combining sample purification and cryo-EM grid preparation into a single step. Here we report a new design of affinity cryo-EM approach, cryo-SPIEM, that applies a traditional pathogen diagnosis tool Solid Phase Immune Electron Microscopy (SPIEM) to the single particle cryo-EM method. This approach provides an alternative, largely simplified and easier to use affinity grid that directly works with most native macromolecular complexes with established antibodies, and enables cryo-EM studies of native samples directly from cell cultures. In the present work, we extensively tested the feasibility of cryo-SPIEM with multiple samples including those of high or low molecular weight, macromolecules with low or high symmetry, His-tagged or native particles, and high- or low-yield macromolecules. Results for all these samples (non-purified His-tagged bacteriophage T7, His-tagged Escherichiacoli ribosomes, native Sindbis virus, and purified but low-concentration native Tulane virus) demonstrated the capability of cryo-SPIEM approach in specifically trapping and concentrating target particles on TEM grids with minimal view constraints for cryo-EM imaging and determination of 3D structures. Copyright © 2014 Elsevier Inc. All rights reserved.
Venkataraman, Aishwarya; Siu, Emily; Sadasivam, Kalaimaran
2016-11-01
Medication errors, including infusion prescription errors are a major public health concern, especially in paediatric patients. There is some evidence that electronic or web-based calculators could minimise these errors. To evaluate the impact of an electronic infusion calculator on the frequency of infusion errors in the Paediatric Critical Care Unit of The Royal London Hospital, London, United Kingdom. We devised an electronic infusion calculator that calculates the appropriate concentration, rate and dose for the selected medication based on the recorded weight and age of the child and then prints into a valid prescription chart. Electronic infusion calculator was implemented from April 2015 in Paediatric Critical Care Unit. A prospective study, five months before and five months after implementation of electronic infusion calculator, was conducted. Data on the following variables were collected onto a proforma: medication dose, infusion rate, volume, concentration, diluent, legibility, and missing or incorrect patient details. A total of 132 handwritten prescriptions were reviewed prior to electronic infusion calculator implementation and 119 electronic infusion calculator prescriptions were reviewed after electronic infusion calculator implementation. Handwritten prescriptions had higher error rate (32.6%) as compared to electronic infusion calculator prescriptions (pharmacy interventions. Use of electronic infusion calculator for infusion prescription significantly reduced the total number of infusion prescribing errors in Paediatric Critical Care Unit and has enabled more efficient use of medical and pharmacy time resources.
Energy Technology Data Exchange (ETDEWEB)
Xie, Xiaohong [School of Chemical Engineering, Inner Mongolia University of Technology, Hohhot 010051 (China); Hao, Dongsheng [School of Chemical Engineering, Inner Mongolia University of Technology, Hohhot 010051 (China); School of Mining and Technology, Inner Mongolia University of Technology, Hohhot 010051 (China); Yang, Jucai, E-mail: yangjc@imut.edu.cn [School of Chemical Engineering, Inner Mongolia University of Technology, Hohhot 010051 (China); School of Energy and Power Engineering, Inner Mongolia University of Technology, Hohhot 010051 (China)
2015-11-05
Highlights: • The ground-state structure of YbSi{sub n} and its anion is substitutional structure. • The four DFT AEAs are in excellent agreement with the experimental data. • Theoretical AEA of 2.33 eV of YbSi{sub 9} is more reasonable than the experimental 2.60 eV. • Hardness analysis reveals that doping Yb to Si{sub n} raises photochemical sensitivity. • Relative stabilities of YbSi{sub n} and their anions are examined. - Abstract: The structures, electron affinities, dissociation energies, hardness, and dipole moments of YbSi{sub n} (n = 4–10) and their anions were examined using B3LYP, TPSSh, PBE and wB97X methods. The lowest-energy structures can be regarded as replacing a Si of the ground-state structure of Si{sub n+1} with a Yb atom. The theoretical adiabatic electron affinities (AEAs) of YbSi{sub n} are in excellent agreement with experimental data. The average absolute errors from experiment are by 0.08, 0.07, 0.05 and 0.08 eV at the B3LYP, the TPSSh, the PBE and the wB97X levels, respectively. Theoretical AEAs of 2.33 ± 0.05 eV for YbSi{sub 9} are more reliable than the experimental value of 2.60 ± 0.05 eV. The hardness analysis reveals that doping Yb atom to Si{sub n} (n = 4–10) clusters raises the photochemical sensitivity. The dissociation energies of Yb atom from YbSi{sub n} and their anions were calculated to examine relative stabilities.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Qibin; Tang, Ning; Brock, Jonathan W.; Mottaz, Heather M.; Ames, Jennifer M.; Baynes, John; Smith, Richard D.; Metz, Thomas O.
2007-06-01
Non-enzymatic glycation of peptides and proteins by D-glucose has important implications in the pathogenesis of diabetes mellitus, particularly in the development of diabetic complications. However, no effective high-throughput methods exist for identifying proteins containing this low abundance post-translational modification in bottom-up proteomic studies. In this report, phenylboronate affinity chromatography was used in a two-step enrichment scheme to selectively isolate first glycated proteins and then glycated, tryptic peptides from human serum glycated in vitro. Enriched peptides were subsequently analyzed by alternating electron transfer dissociation (ETD) and collision induced dissociation (CID) tandem mass spectrometry. It was observed that ETD fragmentation mode resulted in a significantly higher number of glycated peptide identifications (87.6% of all identified peptides) versus CID mode (17.0% of all identified peptides), when utilizing dual glycation enrichment on both the protein and peptide level. This study illustrates that phenylboronate affinity chromatography coupled with LC-MS/MS with ETD as the fragmentation mode is an efficient approach for analyses of glycated proteins and can have broad applications in studies of diabetes mellitus.
Zhang, Qibin; Tang, Ning; Brock, Jonathan W. C.; Mottaz, Heather M.; Ames, Jennifer M.; Baynes, John W.; Smith, Richard D.; Metz, Thomas O.
2008-01-01
Non-enzymatic glycation of peptides and proteins by D-glucose has important implications in the pathogenesis of diabetes mellitus, particularly in the development of diabetic complications. However, no effective high-throughput methods exist for identifying proteins containing this low abundance post-translational modification in bottom-up proteomic studies. In this report, phenylboronate affinity chromatography was used in a two-step enrichment scheme to selectively isolate first glycated proteins and then glycated, tryptic peptides from human serum glycated in vitro. Enriched peptides were subsequently analyzed by alternating electron transfer dissociation (ETD) and collision induced dissociation (CID) tandem mass spectrometry. ETD fragmentation mode permitted identification of a significantly higher number of glycated peptides (87.6% of all identified peptides) versus CID mode (17.0% of all identified peptides), when utilizing enrichment on first the protein and then the peptide level. This study illustrates that phenylboronate affinity chromatography coupled with LC-MS/MS and using ETD as the fragmentation mode is an efficient approach for analysis of glycated proteins and may have broad application in studies of diabetes mellitus. PMID:17488106
The finite difference method in electronic structure calculations
Energy Technology Data Exchange (ETDEWEB)
Fattebert, Jean -Luc [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2015-11-21
Since the development of quantum mechanics, we know the equations describing the behavior of atoms and electrons at the microscopic level. The Schroedinger equation is however too difficult to solve for more than a few particles because of the high dimensional space of the solution - 3N for N particles. So various simplified models have been developed. Furthermore, the first simplification usually introduced is the Born-Oppenhaimer approximation in which atomic nuclei are treated as classical particles surrounded by quantum electrons.
Energy Technology Data Exchange (ETDEWEB)
Hicks, L.D.; Fry, A.J.; Kurzweil, V.C. [Wesleyan University, Middletown, CT (United States). Chemistry Dept.
2004-12-15
The electron affinities (EAs) of a training set of 29 monosubstituted benzalacetophenones (chalcones) were computed at the ab initio density functional B3LYP/6-31G level of theory. The EAs and experimental reduction potentials of the training set are highly linearly correlated (correlation coefficient of 0.969 and standard deviation of 10.8 mV). An additional 72 di-, tri-, and tetrasubstituted chalcones were then synthesized. Their reduction potentials were predicted from computed EAs using the linear correlation derived from the training set. Agreement between the experimental and computed reduction potentials is remarkably good, with a standard deviation of less than 22 mV for this very large set of substances whose potentials extend over a range of almost 700 mV. (author)
Energy Technology Data Exchange (ETDEWEB)
Hicks, L.D.; Fry, A.J.; Kurzweil, V.C. [Wesleyan Univ., Middletown, CT (United States). Hall-Atwater Lab.
2004-12-15
The electron affinities (EAs) of a training set of 29 monosubstituted benzalacetophenones (chalcones) were computed at the ab initio density functional B3LYP/6-31G* level of theory. The EAs and experimental reduction potentials of the training set are highly linearly correlated (correlation coefficient of 0.969 and standard deviation of 10.8 mV). An additional 72 di-, tri-, and tetrasubstituted chalcones were then synthesized. Their reduction potentials were predicted from computed EAs using the linear correlation derived from the training set. Agreement between the experimental and computed reduction potentials is remarkably good, with a standard deviation of less than 22 mV for this very large set of substances whose potentials extend over a range of almost 700 mV. (Author)
Dynamical Mean Field Theory and Electronic Structure Calculations
Chitra, R.; Kotliar, G.
1999-01-01
We formulate the dynamical mean field theory directly in the continuum. For a given definition of the local Green's function, we show the existence of a unique functional, whose stationary point gives the physical local Green's function of the solid. We present the diagrammatic rules to calculate it perturbatively in the interaction. Inspired by the success of dynamical mean field calculations for model Hamiltonian systems, we present approximations to the exact saddle point equations which m...
Saturno, J; Blanco, L; Salas, M; Esteban, J A
1995-12-29
Amino acids Tyr254 and Tyr390 of phi 29 DNA polymerase belong to one of the most conserved regions in eukaryotic-type DNA polymerases. In this paper we report a mutational study of these two residues to address their role in nucleotide selection. This study was carried out by means of a new kinetic analysis that takes advantage of the competition between DNA polymerization and 3'-->5' exonuclease activity to measure the Km values for correct and incorrect nucleotides in steady-state conditions. This method is valid for any 3'-->5' exonuclease-containing DNA polymerase, without any restriction concerning catalytic rates of nucleotide incorporation. The results showed that the discrimination factor achieved by phi 29 DNA polymerase in the nucleotide binding step of DNA polymerization is 2.4 x 10(3), that is, a wrong nucleotide is bound with a 2.4 x 10(3)-fold lower affinity than the correct one. Mutants Y254F, Y390F, and Y390S showed discrimination values of 7.0 x 10(2), > 1.9 x 10(3), and 2.9 x 10(2), respectively. The reduced accuracy of nucleotide binding produced by mutations Y254F and Y390S lead us to propose that phi 29 DNA polymerase residues Tyr254 and Tyr390, highly conserved in eukaryotic-type DNA polymerases, are involved in nucleotide binding selection, thus playing a crucial role in the fidelity of DNA replication. Comparison of the discrimination factors of mutants Y390S and Y390F strongly suggests that the phenyl ring of Tyr390 is directly involved in checking base-pairing correctness of the incoming nucleotide.
Page 1 Electronic structure calculation of Cumn alloy 187 chosen ...
Indian Academy of Sciences (India)
Schwartz (1976). Since neutral atoms were put together to form the cluster, a net charge of zero electron was promoted to the Watson sphere. The atomic value of radius of Cu was assigned as its muffin-tin radius. The radius of Mn was obtained by subtracting the Cu radius from Cu-Mn bond length, so that the muffin-tin ...
First principles calculations of structural, electronic and thermal ...
Indian Academy of Sciences (India)
Administrator
2013-07-28
Jul 28, 2013 ... full-potential linear augmented plane wave (FP-LAPW) method are investigated. The exchange–correlation energy ... The electronic band structure shows that the fundamental energy gap is direct (L–L) for all the compounds. Thermal ... voltaic energy converters (Zogg et al 1994). The semi- conductors PbS ...
First-principle calculations of the structural, electronic ...
Indian Academy of Sciences (India)
For band structure calculations, in addition to WC-GGA approximation, both Engel–Vosko (EV-GGA) generalized gradient approximation and recently proposed modified Becke–Johnson (mBJ) potential approximation have been used. Our investigation on the effect of composition on lattice constant, bulk modulus and band ...
First-principle calculations of structural, electronic, optical, elastic ...
Indian Academy of Sciences (India)
The predicted band gaps using the modified Becke–Johnson(mBJ) exchange approximation are in fairly good agreement with the experimental data. The optical constants such as the dielectric function, refractive index, and the extinction coefficient are calculated and analysed. The independent elastic parameters namely, ...
First-principle calculations of structural, electronic, optical, elastic ...
Indian Academy of Sciences (India)
S CHEDDADI
2017-11-28
Nov 28, 2017 ... The predicted band gaps using the modified Becke–Johnson. (mBJ) exchange approximation are in fairly good agreement with the experimental data. The optical constants such as the dielectric function, refractive index, and the extinction coefficient are calculated and analysed. The independent elastic ...
First-principle calculations of the structural, electronic ...
Indian Academy of Sciences (India)
correlation potential. For band structure calculations, in addition to WC-GGA approximation, both Engel–Vosko. (EV-GGA) generalized gradient approximation and recently proposed modified Becke–Johnson (mBJ) potential approximation have been used. Our investigation on the effect of composition on lattice constant, ...
Improved calculation of the electron self-energy due to electron-phonon coupling in solids
Fortini, A
1998-01-01
An improved method for solving time-dependent problems in quantum mechanics, in the customary cases of constant or harmonic perturbation, is applied to the calculation of the self-energy of electrons interacting with phonons in solids. The mixing of unperturbed Bloch states, resulting from the actual coupling, is self-consistently taken into account, and the related quantum probability amplitudes are determined through direct integration over the quasiparticle spectrum. Laplace transform and elementary mathematics are used, thereby enhancing the physical transparency, and bringing out approximations in every stage. Explicit illustrative results are worked out in the simple case of slowly varying self-energy parameters. The method is critically compared with the standard Green function approach, and further encourages more detailed applications. (author)
First Principles Calculations of Electronic Excitations in 2D Materials
DEFF Research Database (Denmark)
Rasmussen, Filip Anselm
-thin electronics and high efficiency solar cells. Contrary to many other nano-materials, methods for large scale fabrication and patterning have already been demonstrated and the first real technological applications have already be showcased. Still the technology is very young and the number of well-studied 2D...... mechanics methods. One of these methods, Density Functional Theory (DFT), has been very successful at determining structural properties of 2D materials. It is however well-known that it less accurate when it comes to predicting the energy levels of excited states that are important in order to determine...... electronic transport, optical and chemical properties. On the other hand it has shown to be a great starting point for a systematic pertubation theory approach to obtain the so-called quasiparticle spectrum. In the GW approximation one considers the considers the potential from a charged excitation...
Real-space calculations for electron transport properties of nanostructures.
Ono, Tomoya; Tsukamoto, Shigeru; Egami, Yoshiyuki; Fujimoto, Yoshitaka
2011-10-05
Recent developments in the fabrication and investigation of conductors of atomic dimensions have stimulated a large number of experimental and theoretical studies on these nanoscale devices. In this paper, we introduce examples presenting the efficiencies and advantages of a first-principles transport calculation scheme based on the real-space finite-difference (RSFD) formalism and the overbridging boundary-matching (OBM) method. The RSFD method does not suffer from the artificial periodicity problems that arise in methods using plane-wave basis sets or the linear dependence problems that occur in methods using atomic basis sets. Moreover, the algorithm of the RSFD method is suitable for massively parallel computers and, thus, the combination of the RSFD and OBM methods enables us to execute first-principles transport calculations using large models. To demonstrate the advantages of this method, several applications of the transport calculations in various systems ranging from jellium nanowires to the tip and surface system of scanning tunneling microscopy are presented. © 2011 IOP Publishing Ltd
A NEW APPROACH TO THE CALCULATION OF THE THERMODYNAMIC POTENTIAL OF INHOMOGENEOUS ELECTRON GAS
Directory of Open Access Journals (Sweden)
P.P.Kostrobij
2003-01-01
Full Text Available A new approach is proposed to calculate the thermodynamic potential, which consists in reducing the relevant non-Gaussian functional integral to its Gaussian form with a renormalized "density-density" correlator. It is shown that the knowledge of the effective potential of electron-electron interaction is sufficient to calculate the thermodynamic potential in this approach.
Middleton, Kirsten; Zhang, Guoping; George, Thomas F.
2012-02-01
Memantine is currently used as a treatment for mild to severe Alzheimer's disease, although its functionality is complicated. Using various density functional theory calculations and basis sets, we first examine memantine alone and then add ions which are present in the human body. This provides clues as to how the compound may react in the calcium ion channel, where it is believed to treat the disease. In order to understand the difference between calcium and magnesium ions interacting with memantine, we compute the electron affinity of each complex. We find that memantine is more strongly attracted to magnesium ions than calcium ions within the channel. By observing the HOMO-LUMO gap within memantine in comparison to adamantane, we find that memantine is more excitable than the anti-flu drug. We believe these factors to affect the efficiency of memantine as a treatment of Alzheimer's disease.
Calculated and measured dose distribution in electron and X-ray irradiated water phantom
Ziaie, F; Bulka, S; Afarideh, H; Hadji-Saeid, S M
2002-01-01
The Bremsstrahlung yields produced by incident electrons on a tantalum converter have been calculated by using a Monte-Carlo computer code. The tantalum thickness as an X-ray converter was optimized for 2, 2.5, 5, 7.5, and 10 MeV electron beams. The dose distribution in scanning and conveyor direction for both 2 MeV electron and X-ray converted from 2 MeV electron beam have been calculated and compared with experimental results. The economical aspects of low energy electron conversion were discussed as well.
Electron self-energy calculation using a general multi-pole approximation
Soininen, J A; Shirley, E L
2003-01-01
We present a method for calculating the inverse of the dielectric matrix in a solid using a band Lanczos algorithm. The method produces a multi-pole approximation for the inverse dielectric matrix with an arbitrary number of poles. We discuss how this approximation can be used to calculate the screened Coulomb interaction needed for electron self-energy calculations in solids.
Accelerating VASP electronic structure calculations using graphic processing units
Hacene, Mohamed
2012-08-20
We present a way to improve the performance of the electronic structure Vienna Ab initio Simulation Package (VASP) program. We show that high-performance computers equipped with graphics processing units (GPUs) as accelerators may reduce drastically the computation time when offloading these sections to the graphic chips. The procedure consists of (i) profiling the performance of the code to isolate the time-consuming parts, (ii) rewriting these so that the algorithms become better-suited for the chosen graphic accelerator, and (iii) optimizing memory traffic between the host computer and the GPU accelerator. We chose to accelerate VASP with NVIDIA GPU using CUDA. We compare the GPU and original versions of VASP by evaluating the Davidson and RMM-DIIS algorithms on chemical systems of up to 1100 atoms. In these tests, the total time is reduced by a factor between 3 and 8 when running on n (CPU core + GPU) compared to n CPU cores only, without any accuracy loss. © 2012 Wiley Periodicals, Inc.
Calculations for electron-impact excitation and ionization of beryllium
Zatsarinny, Oleg; Fursa, Dmitry V; Bray, Igor
2016-01-01
The B-spline R-matrix and the convergent close-coupling methods are used to study electron collisions with neutral beryllium over an energy range from threshold to 100 eV. Coupling to the target continuum significantly affects the results for transitions from the ground state, but to a lesser extent the strong transitions between excited states. Cross sections are presented for selected transitions between low-lying physical bound states of beryllium, as well as for elastic scattering, momentum transfer, and ionization. The present cross sections for transitions from the ground state from the two methods are in excellent agreement with each other, and also with other available results based on nonperturbative convergent pseudo-state and time-dependent close-coupling models. The elastic cross section at low energies is dominated by a prominent shape resonance. The ionization from the $(2s2p)^3P$ and $(2s2p)^1P$ states strongly depends on the respective term. The current predictions represent an extensive set o...
Monte Carlo calculations of energy deposition distributions of electrons below 20 keV in protein.
Tan, Zhenyu; Liu, Wei
2014-05-01
The distributions of energy depositions of electrons in semi-infinite bulk protein and the radial dose distributions of point-isotropic mono-energetic electron sources [i.e., the so-called dose point kernel (DPK)] in protein have been systematically calculated in the energy range below 20 keV, based on Monte Carlo methods. The ranges of electrons have been evaluated by extrapolating two calculated distributions, respectively, and the evaluated ranges of electrons are compared with the electron mean path length in protein which has been calculated by using electron inelastic cross sections described in this work in the continuous-slowing-down approximation. It has been found that for a given energy, the electron mean path length is smaller than the electron range evaluated from DPK, but it is large compared to the electron range obtained from the energy deposition distributions of electrons in semi-infinite bulk protein. The energy dependences of the extrapolated electron ranges based on the two investigated distributions are given, respectively, in a power-law form. In addition, the DPK in protein has also been compared with that in liquid water. An evident difference between the two DPKs is observed. The calculations presented in this work may be useful in studies of radiation effects on proteins.
Soriano, L; Abbate, M; Pen, H; Prieto, P; Sanz, JM
We studied the electronic structure of TiN and VN by means of band structure calculations and spectroscopic techniques. The band structure calculations show that the bonding in these compounds is mostly covalent. The Fermi level intersects the transition metal 3d bands giving rise to the metallic
RCCC calculations for electron scattering on quasi-two electron targets
Bostock, C.; Fursa, D. V.; Bray, I.
2012-11-01
We report on the recent extension of the RCCC method to accommodate electron scattering from quasi-two electron targets. We present results for electron scattering from mercury (Z = 80) which serves as a testing ground for relativistic theories due to its high atomic number. Furthermore electron-mercury scattering plays an important practical role in the physics of fluorescent and high intensity discharge lamps.
Lin, Lin; Yang, Jucai
2015-06-01
The structures and energies of copper-doped small silicon clusters CuSi n (n = 4-10) and their anions were investigated systematically using CCSD(T)/aug-cc-pVTZ-DK//MP2/6-31G(2df,p), G4//MP2/6-31G(2df,p), and the B3LYP/6-311+G* basis set. The performance of the methods used for the prediction of energetic and thermodynamic properties was evaluated. Comparing experimental [Xu et al. (2012) J Chem Phys 136:104308] and theoretical calculations, it was concluded that the CCSD(T) results are very accurate and exhibit the best performance; the mean absolute deviation from experimental data was 0.043 eV. The excellent agreement of vertical detachment energy (VDE) between experimental results and CCSD(T) calculations indicates that the ground state structures of CuSi n (-) (n = 4-10) presented in this paper are reliable. For CuSi10, assigning 2.90±0.08 eV to the experimental adiabatic electron affinity (AEA) and 3.90±0.08 eV to the VDE is more reasonable than to 3.46±0.08 eV and 3.62±0.08 eV, respectively, based on the CCSD(T) calculations and the previous photoelectron spectrum of CuSi10 (-) (Xu et al., op. cit.). The AEAs of CuSi n (n = 4-10), excluding CuSi7, are in excellent agreement with experimental data, showing that the ground state structures of CuSi n (n = 4-6, 8-10) reported in this paper are reliable. CuSi10 is suggested to be the smallest endohedral ground state structure. However, adding an additional electron to CuSi10 pulls out the Cu atom from the center location, forming an exohedral ground state structure of CuSi10 (-). The charge transfer and dissociation energy of Cu from CuSi n and their anions determined to examine the nature of bonding and their relative stabilities.
Stanke, Monika; Palikot, Ewa; KÈ©dziera, Dariusz; Adamowicz, Ludwik
2016-12-01
An algorithm for calculating the first-order electronic orbit-orbit magnetic interaction correction for an electronic wave function expanded in terms of all-electron explicitly correlated molecular Gaussian (ECG) functions with shifted centers is derived and implemented. The algorithm is tested in calculations concerning the H2 molecule. It is also applied in calculations for LiH and H3+ molecular systems. The implementation completes our work on the leading relativistic correction for ECGs and paves the way for very accurate ECG calculations of ground and excited potential energy surfaces (PESs) of small molecules with two and more nuclei and two and more electrons, such as HeH-, H3+, HeH2, and LiH2+. The PESs will be used to determine rovibrational spectra of the systems.
Han, Sungmin; Kim, Heejin; Kim, Jaehoon; Jung, Yousung
2015-07-14
As a new class of magnetic materials, metal-organic framework (MOF) has received a significant attention due to their functionality and porosity that can provide diverse magnetic phenomena by utilizing host-guest chemistry. For Fe-MOF-74, we here find using density functional calculations that the O2 and C2H4 adsorptions result in the ferromagnetic (FM) and antiferromagnetic (AFM) orderings along the 1D chain of an hexagonal MOF framework, respectively, while their adsorption energies, pi-complexation, and geometrical changes are all similar upon binding. We reveal that this different magnetism behavior is attributed to the different electronic effects, where the adsorbed O2 greatly withdraws a minor spin electron from the Fe centers. The latter significant back donation opens a new channel for superexchange interactions that can enhance the FM coupling between Fe centers, where the strength of calculated intrachain FM coupling constrant (Jin) in O2 adsorbed Fe-MOF-74 is more than 10 times enhanced compared to bare Fe-MOF-74. This prediction suggests a possibility for the conceptual usage of Fe-MOF-74 as a gas sensor based on its magnetic changes caused by the adsorbed gases. Furthermore, the suggested mechanism might be used to control the magnetic properties of MOFs using the guest molecules, although concrete strategies to enhance such magnetic interactions to be used in practical applications would require further significant investigation.
Monte Carlo calculation of large and small-angle electron scattering in air
Cohen, B. I.; Higginson, D. P.; Eng, C. D.; Farmer, W. A.; Friedman, A.; Grote, D. P.; Larson, D. J.
2017-11-01
A Monte Carlo method for angle scattering of electrons in air that accommodates the small-angle multiple scattering and larger-angle single scattering limits is introduced. The algorithm is designed for use in a particle-in-cell simulation of electron transport and electromagnetic wave effects in air. The method is illustrated in example calculations.
Energy Technology Data Exchange (ETDEWEB)
Fujimoto, Kazuhiro J., E-mail: fujimoto@ruby.kobe-u.ac.jp [Department of Computational Science, Graduate School of System Informatics, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501 (Japan)
2014-12-07
A transition charge, dipole, and quadrupole from electrostatic potential (TrESP-CDQ) method for electronic coupling calculations is proposed. The TrESP method is based on the classical description of electronic Coulomb interaction between transition densities for individual molecules. In the original TrESP method, only the transition charge interactions were considered as the electronic coupling. In the present study, the TrESP method is extended to include the contributions from the transition dipoles and quadrupoles as well as the transition charges. Hence, the self-consistent transition density is employed in the ESP fitting procedure. To check the accuracy of the present approach, several test calculations are performed to a helium dimer, a methane dimer, and an ethylene dimer. As a result, the TrESP-CDQ method gives a much improved description of the electronic coupling, compared with the original TrESP method. The calculated results also show that the self-consistent treatment to the transition densities contributes significantly to the accuracy of the electronic coupling calculations. Based on the successful description of the electronic coupling, the contributions to the electronic coupling are also analyzed. This analysis clearly shows a negligible contribution of the transition charge interaction to the electronic coupling. Hence, the distribution of the transition density is found to strongly influence the magnitudes of the transition charges, dipoles, and quadrupoles. The present approach is useful for analyzing and understanding the mechanism of excitation-energy transfer.
Calculation of two-center one-electron molecular integrals with STOs. [BICEN
Energy Technology Data Exchange (ETDEWEB)
Rico, J.F.; Lopez, R.; Paniagua, M.; Ramirez, G. (Universidad Autonoma de Madrid (Spain). Dept. de Quimica Fisica y Quimica Cuantica)
1991-05-01
A program for the calculation of two-center one-electron integrals (overlap, nuclear attraction and kinetic energy) between real Slater-type orbitals (STOs) is reported. The integrals are obtained by recursion over simple auxiliary matrices, whose elements are calculated in terms of further auxiliary functions evaluated in a quick and accurate way. (orig.).
Hot-electron-mediated desorption rates calculated from excited-state potential energy surfaces
DEFF Research Database (Denmark)
Olsen, Thomas; Gavnholt, Jeppe; Schiøtz, Jakob
2009-01-01
We present a model for desorption induced by (multiple) electronic transitions [DIET (DIMET)] based on potential energy surfaces calculated with the delta self-consistent field extension of density-functional theory. We calculate potential energy surfaces of CO and NO molecules adsorbed on variou...
Eikhorn, Yu. L.; Korotchenko, K. B.; Pivovarov, Yu. L.; Tukhfatullin, T. A.
2017-07-01
The first experiment on electronuclear reaction initated by axially channeled 700 MeV electrons in a Si crystal [1] revealed remarkable depth oscillations of reaction yield. The effect was satisfactory explained [2] by computer simulations using binary collisions model. In this work the oscillations effect is investigated for planar channeled electrons in a Si crystal using the new computer code BCM-1.0 which allows both classical and quantum calculations of channeled electrons flux density.
Serov, Vladislav V; Sergeeva, Tatiana A; Vinitsky, Sergue I
2012-01-01
A review of some recently developed methods of calculating multiple differential cross-sections of photoionization and electron impactionization of atoms and molecules having two active electrons is presented. The methods imply original approaches to calculating three-particle Coulomb wave functions. The external complex scaling method and the formalism of the Schroedinger equation with a source in the right-hand side are considered. Efficiency of the time-dependent approaches to the scattering problem, such as the paraxial approximation and the time-dependent scaling, is demonstrated. An original numerical method elaborated by the authors for solving the 6D Schroedinger equation for an atom with two active electrons, based on the Chang-Fano transformation and the discrete variable representation, is formulated. Basing on numerical simulations, the threshold behavior of angular distributions of two-electron photoionization of the negative hydrogen ion and helium atom, and multiple differential cross-sections ...
R-matrix calculation of low-energy electron collisions with phosphoric acid
Energy Technology Data Exchange (ETDEWEB)
Bryjko, Lilianna; Van Mourik, Tanja [School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST (United Kingdom); Dora, Amar; Tennyson, Jonathan, E-mail: j.tennyson@ucl.ac.u [Department of Physics and Astronomy, University College London, Gower St, London WC1E 6BT (United Kingdom)
2010-12-14
Electron collision calculations are performed on two conformers of H{sub 3}PO{sub 4}, a weakly dipolar form with all OH groups pointing up and a strongly dipolar form where one OH group points down. Strong evidence is found for a broad shape resonance at about 7 eV for both conformers, although the precise parameters of this resonance are sensitive to the details of the target wavefunction used. Ten-state close-coupling calculations suggest the presence of very narrow Feshbach resonances in a similar energy region. Again both conformers behave similarly. Elastic and electronically inelastic cross sections are calculated for both conformers.
R-matrix calculation of electron collisions with the BF{sup +} molecular ion
Energy Technology Data Exchange (ETDEWEB)
Chakrabarti, K [Department of Mathematics, Scottish Church College, 1 and 3 Urquhart Sq, Kolkata 700006 (India); Tennyson, Jonathan [Department of Physics and Astronomy, University College London, Gower St, London WC1E 6BT (United Kingdom)
2009-05-28
Electron collisions with the BF{sup +} molecular ion are studied using the framework of the diatomic version of the UK molecular R-matrix codes. A configuration-interaction calculation is performed for BF{sup +} to obtain potential energy curves and target properties for 14 lowest doublet and quartet states. Scattering calculations are performed which yield resonance parameters and excitation cross sections in the energy range 0-20 eV. Cross sections for rotational excitations and an approximate calculation for the electron impact dissociation cross section for BF{sup +} are also presented.
AMORPHOUS SILICON ELECTRONIC STRUCTURE MODELING AND BASIC ELECTRO-PHYSICAL PARAMETERS CALCULATION
Directory of Open Access Journals (Sweden)
B. A. Golodenko
2014-01-01
Full Text Available Summary. The amorphous semiconductor has any unique processing characteristics and it is perspective material for electronic engineering. However, we have not authentic information about they atomic structure and it is essential knot for execution calculation they electronic states and electro physical properties. The author's methods give to us decision such problem. This method allowed to calculation the amorphous silicon modeling cluster atomics Cartesian coordinates, determined spectrum and density its electronic states and calculation the basics electro physical properties of the modeling cluster. At that determined numerical means of the energy gap, energy Fermi, electron concentration inside valence and conduction band for modeling cluster. The find results provides real ability for purposeful control to type and amorphous semiconductor charge carriers concentration and else provides relation between atomic construction and other amorphous substance physical properties, for example, heat capacity, magnetic susceptibility and other thermodynamic sizes.
DEFF Research Database (Denmark)
Sauer, Stephan P. A.; Paidarová, Ivana; Čársky, Petr
2016-01-01
In this paper we present calculations of the static polarizability and its derivatives for the adamantane molecule carried out at the density functional theory level using the B3LYP exchange correlation functional and Sadlej’s polarized valence triple zeta basis set. It is shown that the polariza......In this paper we present calculations of the static polarizability and its derivatives for the adamantane molecule carried out at the density functional theory level using the B3LYP exchange correlation functional and Sadlej’s polarized valence triple zeta basis set. It is shown...... that the polarizability tensor is necessary to correct long-range behavior of DFT functionals used in electron-molecule scattering calculations. The impact of such a long-range correction is demonstrated on elastic and vibrationally inelastic electron collisions with adamantane, a molecule representing a large polyatomic...... target for electron scattering calculations....
Energy Technology Data Exchange (ETDEWEB)
Piñera, Ibrahin, E-mail: ipinera@ceaden.edu.cu [Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear, CEADEN, 30 St. 502, Playa 11300, Havana (Cuba); Cruz, Carlos M.; Leyva, Antonio; Abreu, Yamiel; Cabal, Ana E. [Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear, CEADEN, 30 St. 502, Playa 11300, Havana (Cuba); Espen, Piet Van; Remortel, Nick Van [University of Antwerp, CGB, Groenenborgerlaan 171, 2020 Antwerpen (Belgium)
2014-11-15
Highlights: • We present a calculation procedure for dpa cross section in solids under irradiation. • Improvement about 10–90% for the gamma irradiation induced dpa cross section. • Improvement about 5–50% for the electron irradiation induced dpa cross section. • More precise results (20–70%) for thin samples irradiated with electrons. - Abstract: Several authors had estimated the displacements per atom cross sections under different approximations and models, including most of the main gamma- and electron-material interaction processes. These previous works used numerical approximation formulas which are applicable for limited energy ranges. We proposed the Monte Carlo assisted Classical Method (MCCM), which relates the established theories about atom displacements to the electron and positron secondary fluence distributions calculated from the Monte Carlo simulation. In this study the MCCM procedure is adapted in order to estimate the displacements per atom cross sections for gamma and electron irradiation. The results obtained through this procedure are compared with previous theoretical calculations. An improvement in about 10–90% for the gamma irradiation induced dpa cross section is observed in our results on regard to the previous evaluations for the studied incident energies. On the other hand, the dpa cross section values produced by irradiation with electrons are improved by our calculations in about 5–50% when compared with the theoretical approximations. When thin samples are irradiated with electrons, more precise results are obtained through the MCCM (in about 20–70%) with respect to the previous studies.
DEFF Research Database (Denmark)
Buchardt, Kristian
2016-01-01
Affine processes possess the property that expectations of exponential affine transformations are given by a set of Riccati differential equations, which is the main feature of this popular class of processes. In this paper we generalise these results for expectations of more general transformati......Affine processes possess the property that expectations of exponential affine transformations are given by a set of Riccati differential equations, which is the main feature of this popular class of processes. In this paper we generalise these results for expectations of more general...... transformations. This is of interest in, e.g. doubly stochastic Markov models, in particular in life insurance. When using affine processes for modelling the transition rates and interest rate, the results presented allow for easy calculation of transition probabilities and expected present values....
Gove, S. K.; Gropen, O.; Fægri, K.; Haaland, A.; Martinsen, K.-G.; Strand, T. G.; Volden, H. V.; Swang, O.
1999-08-01
The molecular structure of NbCl 5 was determined experimentally by gas electron diffraction and computationally by structure optimisation of D 3h models. The bond distances obtained by ab initio calculations with very large basis sets, relativistic effects included through the one-electron Douglas-Kroll method and all electrons correlated at the MP2 level and by gas electron diffraction are: (calc/exp) Nb-Cl ax=230.7/230.6(5) pm and Nb-Cl eq=227.0/227.5(4) pm.
Liu, Wei; Tan, Zhenyu; Zhang, Liming; Champion, Christophe
2017-03-01
In this work, direct DNA damage induced by low-energy electrons (sub-keV) is simulated using a Monte Carlo method. The characteristics of the present simulation are to consider the new mechanism of DNA damage due to dissociative electron attachment (DEA) and to allow determining damage to specific bases (i.e., adenine, thymine, guanine, or cytosine). The electron track structure in liquid water is generated, based on the dielectric response model for describing electron inelastic scattering and on a free-parameter theoretical model and the NIST database for calculating electron elastic scattering. Ionization cross sections of DNA bases are used to generate base radicals, and available DEA cross sections of DNA components are applied for determining DNA-strand breaks and base damage induced by sub-ionization electrons. The electron elastic scattering from DNA components is simulated using cross sections from different theoretical calculations. The resulting yields of various strand breaks and base damage in cellular environment are given. Especially, the contributions of sub-ionization electrons to various strand breaks and base damage are quantitatively presented, and the correlation between complex clustered DNA damage and the corresponding damaged bases is explored. This work shows that the contribution of sub-ionization electrons to strand breaks is substantial, up to about 40-70%, and this contribution is mainly focused on single-strand break. In addition, the base damage induced by sub-ionization electrons contributes to about 20-40% of the total base damage, and there is an evident correlation between single-strand break and damaged base pair A-T.
Electronic states and nature of bonding in the molecule MoC by all electron ab initio calculations
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, Karl A.
1997-01-01
by solving the Schrodinger equation for the nuclear motion numerically. Based on the results of the CASSCF calculations the (3) Sigma(-) ground state of MoC is separated from the excited states (3) Delta, (5) Sigma-, (1) Sigma, (1) Delta, (5) Pi, (1) Sigma(+), and (3) Pi by transition energies of 4500, 6178...... Darwin contact term and the relativistic mass-velocity correction have been determined in perturbation calculations. The electronic ground state is predicted as (3) Sigma(-). The spectroscopic constants for the (3) Sigma(-) electronic ground state and eight low-lying excited states have been derived......, 7207, 9312, 10 228, 11 639, and 16 864 cm(-1), respectively. The transition energy between the (3) Sigma(-) ground state and the (3) Pi state as derived in the MRCI calculations is 15 484 cm(-1). For the (3) Sigma(-) ground state the equilibrium distance has been determined as 1.688 Angstrom...
Output calculation of electron therapy at extended SSD using an improved LBR method
Energy Technology Data Exchange (ETDEWEB)
Alkhatib, Hassaan A.; Gebreamlak, Wondesen T., E-mail: wondtassew@gmail.com; Wright, Ben W.; Neglia, William J. [South Carolina Oncology Associates, Columbia, South Carolina 29210 (United States); Tedeschi, David J. [Department of Physics and Astronomy, University of South Carolina, Columbia, South Carolina 29208 (United States); Mihailidis, Dimitris [CAMC Cancer Center and Alliance Oncology, Charleston, West Virginia 25304 (United States); Sobash, Philip T. [The Medical University of South Carolina, Charleston, South Carolina 29425 (United States); Fontenot, Jonas D. [Department of Physics, Mary Bird Perkins Cancer Center, Baton Rouge, Louisiana 70809 (United States)
2015-02-15
Purpose: To calculate the output factor (OPF) of any irregularly shaped electron beam at extended SSD. Methods: Circular cutouts were prepared from 2.0 cm diameter to the maximum possible size for 15 × 15 applicator cone. In addition, two irregular cutouts were prepared. For each cutout, percentage depth dose (PDD) at the standard SSD and doses at different SSD values were measured using 6, 9, 12, and 16 MeV electron beam energies on a Varian 2100C LINAC and the distance at which the central axis electron fluence becomes independent of cutout size was determined. The measurements were repeated with an ELEKTA Synergy LINAC using 14 × 14 applicator cone and electron beam energies of 6, 9, 12, and 15 MeV. The PDD measurements were performed using a scanning system and two diodes—one for the signal and the other a stationary reference outside the tank. The doses of the circular cutouts at different SSDs were measured using PTW 0.125 cm{sup 3} Semiflex ion-chamber and EDR2 films. The electron fluence was measured using EDR2 films. Results: For each circular cutout, the lateral buildup ratio (LBR) was calculated from the measured PDD curve using the open applicator cone as the reference field. The effective SSD (SSD{sub eff}) of each circular cutout was calculated from the measured doses at different SSD values. Using the LBR value and the radius of the circular cutout, the corresponding lateral spread parameter [σ{sub R}(z)] was calculated. Taking the cutout size dependence of σ{sub R}(z) into account, the PDD curves of the irregularly shaped cutouts at the standard SSD were calculated. Using the calculated PDD curve of the irregularly shaped cutout along with the LBR and SSD{sub eff} values of the circular cutouts, the output factor of the irregularly shaped cutout at extended SSD was calculated. Finally, both the calculated PDD curves and output factor values were compared with the measured values. Conclusions: The improved LBR method has been generalized to
Zhu, Xiao-Qing; Liu, Qiao-Yun; Chen, Qiang; Mei, Lian-Rui
2010-02-05
A series of 61 imines with various typical structures were synthesized, and the thermodynamic affinities (defined as enthalpy changes or redox potentials in this work) of the imines to abstract hydride anions, hydrogen atoms, and electrons, the thermodynamic affinities of the radical anions of the imines to abstract hydrogen atoms and protons, and the thermodynamic affinities of the hydrogen adducts of the imines to abstract electrons in acetonitrile were determined by using titration calorimetry and electrochemical methods. The pure heterolytic and homolytic dissociation energies of the C=N pi-bond in the imines were estimated. The polarity of the C=N double bond in the imines was examined using a linear free-energy relationship. The idea of a thermodynamic characteristic graph (TCG) of imines as an efficient "Molecule ID Card" was introduced. The TCG can be used to quantitatively diagnose and predict the characteristic chemical properties of imines and their various reaction intermediates as well as the reduction mechanism of the imines. The information disclosed in this work could not only supply a gap of thermodynamics for the chemistry of imines but also strongly promote the fast development of the applications of imines.
Directory of Open Access Journals (Sweden)
H. K. A. Nguyen
2018-01-01
Full Text Available The suppression of secondary electron yield (SEY which can possibly lead to multipactor is an important goal for several applications. Though some techniques have focused on geometric modifications to lower the SEY, the use of graphene coatings as thin as a few monolayers is a promising new development that deserves attention either as a standalone technique or in concert with geometric alterations. Here we report on Monte Carlo based numerical studies of SEY on graphene coated copper with comparisons to recent experimental data. Our predicted values are generally in good agreement with reported measurements. Suppression of the secondary electron yield by as much as 50 percent (over copper with graphene coating is predicted at energies below 125 eV, and bodes well for multipactor suppression in radio frequency applications.
Nguyen, H. K. A.; Mankowski, J.; Dickens, J. C.; Neuber, A. A.; Joshi, R. P.
2018-01-01
The suppression of secondary electron yield (SEY) which can possibly lead to multipactor is an important goal for several applications. Though some techniques have focused on geometric modifications to lower the SEY, the use of graphene coatings as thin as a few monolayers is a promising new development that deserves attention either as a standalone technique or in concert with geometric alterations. Here we report on Monte Carlo based numerical studies of SEY on graphene coated copper with comparisons to recent experimental data. Our predicted values are generally in good agreement with reported measurements. Suppression of the secondary electron yield by as much as 50 percent (over copper) with graphene coating is predicted at energies below 125 eV, and bodes well for multipactor suppression in radio frequency applications.
The Skyrme-TQRPA calculations of electron capture on hot nuclei in pre-supernova environment
Energy Technology Data Exchange (ETDEWEB)
Dzhioev, Alan A., E-mail: dzhioev@theor.jinr.ru; Vdovin, A. I., E-mail: vdovin@theor.jinr.ru [JINR, Bogoliubov Laboratory of Theoretical Physics (Russian Federation); Stoyanov, Ch., E-mail: stoyanov@inrne.bas.bg [Bulgarian Academy of Sciences, Institute for Nuclear Research and Nuclear Energy (Bulgaria)
2016-11-15
We combine the thermal QRPA approach with the Skyrme energy density functional theory (Skyrme–TQRPA) for modelling the process of electron capture on nuclei in supernova environment. For a sample nucleus, {sup 56}Fe, the Skyrme–TQRPA approach is applied to analyze thermal effects on the strength function of GT{sub +} transitions which dominate electron capture at E{sub e} ≤ 30 MeV. Several Skyrme interactions are used in order to verify the sensitivity of the obtained results to the Skyrme force parameters. Finite-temperature cross sections are calculated and the results are comparedwith those of the other model calculations.
Calculation of the transverse kicks generated by the bends of a hollow electron lens
Energy Technology Data Exchange (ETDEWEB)
Stancari, Giulio
2014-03-25
Electron lenses are pulsed, magnetically confined electron beams whose current-density profile is shaped to obtain the desired effect on the circulating beam in high-energy accelerators. They were used in the Fermilab Tevatron collider for abort-gap clearing, beam-beam compensation, and halo scraping. A beam-beam compensation scheme based upon electron lenses is currently being implemented in the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. This work is in support of a conceptual design of hollow electron beam scraper for the Large Hadron Collider. It also applies to the implementation of nonlinear integrable optics with electron lenses in the Integrable Optics Test Accelerator at Fermilab. We consider the axial asymmetries of the electron beam caused by the bends that are used to inject electrons into the interaction region and to extract them. A distribution of electron macroparticles is deposited on a discrete grid enclosed in a conducting pipe. The electrostatic potential and electric fields are calculated using numerical Poisson solvers. The kicks experienced by the circulating beam are estimated by integrating the electric fields over straight trajectories. These kicks are also provided in the form of interpolated analytical symplectic maps for numerical tracking simulations, which are needed to estimate the effects of the electron lens imperfections on proton lifetimes, emittance growth, and dynamic aperture. We outline a general procedure to calculate the magnitude of the transverse proton kicks, which can then be generalized, if needed, to include further refinements such as the space-charge evolution of the electron beam, magnetic fields generated by the electron current, and longitudinal proton dynamics.
Calculated low-energy electron-impact vibrational excitation cross sections for CO2 molecule
Laporta, V; Celiberto, R
2016-01-01
Vibrational-excitation cross sections of ground electronic state of carbon dioxide molecule by electron-impact through the CO2-(2\\Pi) shape resonance is considered in the separation of the normal modes approximation. Resonance curves and widths are computed for each vibrational mode. The calculations assume decoupling between normal modes and employ the local complex potential model for the treatment of the nuclear dynamics, usually adopted for the electron-scattering involving diatomic molecules. Results are presented for excitation up to 10 vibrational levels in each mode and comparison with data present in the literature is discussed.
Multiconfiguration calculations of electronic isotope-shift factors in Zn i
Filippin, Livio; Bieroń, Jacek; Gaigalas, Gediminas; Godefroid, Michel; Jönsson, Per
2017-10-01
The present work reports results from systematic multiconfiguration Dirac-Hartree-Fock calculations of electronic isotope-shift factors for a set of transitions between low-lying states in neutral zinc. These electronic quantities, together with observed isotope shifts between different pairs of isotopes, provide the changes in mean-square charge radii of the atomic nuclei. Within this computational approach, different models for electron correlation are explored in a systematic way to determine a reliable computational strategy and to estimate theoretical error bars of the isotope-shift factors.
SU-F-BRCD-03: Dose Calculation of Electron Therapy Using Improved Lateral Buildup Ratio Method.
Gebreamlak, W; Tedeschi, D; Alkhatib, H
2012-06-01
To calculate the percentage depth dose of any irregular shape electron beam using modified lateral build-up-ratio method. Percentage depth dose (PDD) curves were measured using 6, 9, 12, and 15MeV electron beam energies for applicator cone sizes of 6×6, 10×10, 14×14, and 14×14cm2 . Circular cutouts for each cone were prepared from 2.0cm diameter to the maximum possible size for each cone. In addition, three irregular cutouts were prepared. The scanning was done using a water tank and two diodes - one for the signal and the other a stationary reference outside the tank. The water surface was determined by scanning the signal diode slowly from water to air and by noting the sharp change of the percentage depth dose curve at the water/air interface. The lateral build-up-ratio (LBR) for each circular cutout was calculated from the measured PDD curve using the open field of the 14×14 cm2 cone as the reference field. Using the LBR values and the radius of the circular cutouts, the corresponding lateral spread parameter (sigma) of the electron shower was calculated. Unlike the commonly accepted assumption that sigma is independent of cutout size, it is shown that the sigma value increases linearly with circular cutout size. Using this characteristic of sigma, the PDD curves of irregularly shaped cutouts were calculated. Finally, the calculated PDD curves were compared with measured PDD curves. In this research, it is shown that sigma increases with cutout size. For radius of circular cutout sizes up to the equilibrium range of the electron beam, the increase of sigma with the cutout size is linear. The percentage difference of the calculated PDD from the measured PDD for irregularly shaped cutouts was under 1.0%. Similar Result was obtained for four electron beam energies (6, 9, 12, and 15MeV). © 2012 American Association of Physicists in Medicine.
DEFF Research Database (Denmark)
Strange, M.; Rostgaard, Carsten; Hakkinen, H.
2011-01-01
(exchange) on the molecule and dynamical screening at the metal-molecule interface. The main effect of the GW self-energy is to renormalize the level positions; however, its influence on the shape of molecular resonances also affects the conductance. Non-self-consistent G(0)W(0) calculations, starting from......The electronic conductance of a benzene molecule connected to gold electrodes via thiol, thiolate, or amino anchoring groups is calculated using nonequilibrium Green functions in combination with the fully self-consistent GW approximation for exchange and correlation. The calculated conductance...
Energy Technology Data Exchange (ETDEWEB)
Cobut, V.; Frongillo, Y.; Jay-Gerin, J.-P. (Sherbrooke Univ., PQ (Canada). Faculte de Medecine); Patau, J.-P. (Toulouse-3 Univ., 31 (France))
1992-12-01
An energy spectrum of ''subexcitation electrons'' produced in liquid water by electrons with initial energies of a few keV is obtained by using a Monte Carlo transport simulation calculation. It is found that the introduction of vibrational-excitation cross sections leads to the appearance of a sharp peak in the probability density function near the electronic-excitation threshold. Electrons contributing to this peak are shown to be more naturally described if a novel energy spectrum, that we propose to name ''vibrationally-relaxing electron'' spectrum, is introduced. The corresponding distribution function is presented, and an empirical expression of it is given. (author).
first-principle calculation of electrons charge density in the diamond
African Journals Online (AJOL)
DR. AMINU
the direct lattice. Table 1, below lists some elements which exhibit the diamond structure. The nearest neighbor distance, d is calculated from the appropriate ..... Slater, J. C. (1955). One-Electron Energies of Atoms,. Molecules and Solids Phys. Rev. 98, 1039. Seeger, K. (2004). Semiconductor Physics (Springer-Verlag.
Miniworkshop on Methods of Electronic Structure Calculations and Working Group on Disordered Alloys
Andersen, O K; Mookerjee, A
1994-01-01
Developments in the density functional theory and the methods of electronic structure calculations have made it possible to carry out ab-initio studies of a variety of materials efficiently and at a predictable level. This book covers many of those state-of-the-art developments and their applications to ordered and disordered materials, surfaces and interfaces and clusters, etc.
DEFF Research Database (Denmark)
Fürst, Joachim Alexander; Hashemi, J.; Markussen, Troels
2009-01-01
techniques and tight-binding calculations to illustrate these materials' transmission properties and give physical arguments to interpret the numerical results. Specifically, above the Fermi energy we find a strong reduction in electron transmission due to localized states in certain regions of the structure...
Dirac-Fock atomic electronic structure calculations using different nuclear charge distributions
Visscher, L; Dyall, KG
1997-01-01
Numerical Hartree-Fock calculations based on the Dirac-Coulomb Hamiltonian for the first 109 elements of the periodic table are presented. The results give the total electronic energy, as a function of the nuclear model that is used, for four different models of the nuclear charge distribution. The
A Technique for Temperature and Ultimate Load Calculations of Thin Targets in a Pulsed Electron Beam
DEFF Research Database (Denmark)
Hansen, Jørgen-Walther; Lundsager, Per
1979-01-01
A technique is presented for the calculation of transient temperature distributions and ultimate load of rotationally symmetric thin membranes with uniform lateral load and exposed to a pulsed electron beam from a linear accelerator. Heat transfer by conduction is considered the only transfer...
DEFF Research Database (Denmark)
Hedegård, Erik Donovan; Kongsted, Jacob; Sauer, Stephan P. A.
2012-01-01
Calculation of hyperfine coupling constants (HFCs) of Electron Paramagnetic Resonance from first principles can be a beneficial compliment to experimental data in cases where the molecular structure is unknown. We have recently investigated basis set convergence of HFCs in d-block complexes...
Calculation of differential cross section for dielectronic recombination with two-electron uranium
Lyashchenko, Konstantin N.; Andreev, Oleg Yu.
2016-01-01
Calculation of the differential cross section for the dielectronic recombination with two-electron uranium within the framework of QED is presented. The polarization of the emitted photon is investigated. The contributions of the Breit interaction and the interference of the photon multipoles are studied.
Sun, Haitao
2016-05-16
We propose a new methodology for the first-principles description of the electronic properties relevant for charge transport in organic molecular crystals. This methodology, which is based on the combination of a non-empirical, optimally tuned range-separated hybrid functional with the polarizable continuum model, is applied to a series of eight representative molecular semiconductor crystals. We show that it provides ionization energies, electron affinities, and transport gaps in very good agreement with experimental values as well as with the results of many-body perturbation theory within the GW approximation at a fraction of the computational costs. Hence, this approach represents an easily applicable and computationally efficient tool to estimate the gas-to-crystal-phase shifts of the frontier-orbital quasiparticle energies in organic electronic materials.
Electronic properties of tantalum pentoxide polymorphs from first-principles calculations
Lee, J.; Lu, W.; Kioupakis, E.
2014-11-01
Tantalum pentoxide (Ta2O5) is extensively studied for its attractive properties in dielectric films, anti-reflection coatings, and resistive switching memory. Although various crystalline structures of tantalum pentoxide have been reported, its structural, electronic, and optical properties still remain a subject of research. We investigate the electronic and optical properties of crystalline and amorphous Ta2O5 structures using first-principles calculations based on density functional theory and the GW method. The calculated band gaps of the crystalline structures are too small to explain the experimental measurements, but the amorphous structure exhibits a strong exciton binding energy and an optical band gap (˜4 eV) in agreement with experiment. We determine the atomic orbitals that constitute the conduction band for each polymorph and analyze the dependence of the band gap on the atomic geometry. Our results establish the connection between the underlying structure and the electronic and optical properties of Ta2O5.
Directory of Open Access Journals (Sweden)
A Parvazian
2010-12-01
Full Text Available Fast ignition is a new method for inertial confinement fusion (ICF in which the compression and ignition steps are separated. In the first stage, fuel is compressed by laser or ion beams. In the second phase, relativistic electrons are generated by pettawat laser in the fuel. Also, in the second phase 5-35 MeV protons can be generated in the fuel. Electrons or protons can penetrate in to the ultra-dense fuel and deposit their energy in the fuel . More recently, cylindrical rather than spherical fuel chambers with magnetic control in the plasma domain have been also considered. This is called magnetized target fusion (MTF. Magnetic field has effects on relativistic electrons energy deposition rate in fuel. In this work, fast ignition method in cylindrical fuel chambers is investigated and transportation of the relativistic electrons and protons is calculated using MCNPX and FLUKA codes with 0. 25 and 0. 5 tesla magnetic field in single and dual hot spot. Furthermore, the transfer rate of relativistic electrons and high energy protons to the fuel and fusion gain are calculated. The results show that the presence of external magnetic field guarantees higher fusion gain, and relativistic electrons are much more appropriate objects for ignition. MTF in dual hot spot can be considered as an appropriate substitution for the current ICF techniques.
Malyk, O. P.; Syrotyuk, S. V.
2018-01-01
The present article deals with the description of electron scattering on the different types of point defects in zinc blende ZnSe on the basis of short-range principles. The electron interaction with polar and nonpolar optical phonons, piezoelectric and acoustic phonons, neutral and ionized impurities and static strain centers is considered. The electron transition probabilities and, respectively, the kinetic coefficients in zinc selenide, were calculated using the numerical eigenfunction and self-consistent potential obtained within the ab initio density functional theory. The latter were evaluated using the projector augmented waves formalism as implemented in the ABINIT software suite. We investigated ZnSe samples with defect concentration 4.7 × 1015-1.08 × 1017 cm-3 , then calculated temperature dependencies of electron mobility and Hall factors in the range of 20-400 K. It is shown that the theoretical curves obtained in the framework of short-range scattering models much better coincide with experimental data than the curves calculated on the basis of long-range scattering models.
Energetics of intrinsic point defects in uranium dioxide from electronic-structure calculations
Energy Technology Data Exchange (ETDEWEB)
Nerikar, Pankaj; Watanabe, Taku [Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 (United States); Tulenko, James S. [Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, FL 32611 (United States); Phillpot, Simon R. [Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 (United States); Sinnott, Susan B. [Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 (United States)], E-mail: ssinn@mse.ufl.edu
2009-01-31
The stability range of intrinsic point defects in uranium dioxide is determined as a function of temperature, oxygen partial pressure, and non-stoichiometry. The computational approach integrates high accuracy ab initio electronic-structure calculations and thermodynamic analysis supported by experimental data. In particular, the density functional theory calculations are performed at the level of the spin polarized, generalized gradient approximation and includes the Hubbard U term; as a result they predict the correct anti-ferromagnetic insulating ground state of uranium oxide. The thermodynamic calculations enable the effects of system temperature and partial pressure of oxygen on defect formation energy to be determined. The predicted equilibrium properties and defect formation energies for neutral defect complexes match trends in the experimental literature quite well. In contrast, the predicted values for charged complexes are lower than the measured values. The calculations predict that the formation of oxygen interstitials becomes increasingly difficult as higher temperatures and reducing conditions are approached.
Al-Refaie, Ahmed F.; Tennyson, Jonathan
2017-12-01
Construction and diagonalization of the Hamiltonian matrix is the rate-limiting step in most low-energy electron - molecule collision calculations. Tennyson (1996) implemented a novel algorithm for Hamiltonian construction which took advantage of the structure of the wavefunction in such calculations. This algorithm is re-engineered to make use of modern computer architectures and the use of appropriate diagonalizers is considered. Test calculations demonstrate that significant speed-ups can be gained using multiple CPUs. This opens the way to calculations which consider higher collision energies, larger molecules and / or more target states. The methodology, which is implemented as part of the UK molecular R-matrix codes (UKRMol and UKRMol+) can also be used for studies of bound molecular Rydberg states, photoionization and positron-molecule collisions.
Energy Technology Data Exchange (ETDEWEB)
Xie, M. [Lawrence Berkeley Lab., CA (United States)
1995-12-31
I present an exact calculation of free-electron-laser (FEL) eigenmodes (fundamental as well as higher order modes) in the exponential-gain regime. These eigenmodes specify transverse profiles and exponential growth rates of the laser field, and they are self-consistent solutions of the coupled Maxwell-Vlasov equations describing the FEL interaction taking into account the effects due to energy spread, emittance and betatron oscillations of the electron beam, and diffraction and guiding of the laser field. The unperturbed electron distribution is assumed to be of Gaussian shape in four dimensional transverse phase space and in the energy variable, but uniform in longitudinal coordinate. The focusing of the electron beam is assumed to be matched to the natural wiggler focusing in both transverse planes. With these assumptions the eigenvalue problem can be reduced to a numerically manageable integral equation and solved exactly with a kernel iteration method. An approximate, but more efficient solution of the integral equation is also obtained for the fundamental mode by a variational technique, which is shown to agree well with the exact results. Furthermore, I present a handy formula, obtained from interpolating the numerical results, for a quick calculation of FEL exponential growth rate. Comparisons with simulation code TDA will also be presented. Application of these solutions to the design and multi-dimensional parameter space optimization for an X-ray free electron laser driven by SLAC linac will be demonstrated. In addition, a rigorous analysis of transverse mode degeneracy and hence the transverse coherence of the X-ray FEL will be presented based on the exact solutions of the higher order guided modes.
Numerical calculations of the electron beam emittance for laser acceleration experiments
Balascuta, Septimiu
2017-06-01
At the E6 experimental area at ELI-NP, two 10 PW Laser (pump and probe) pulses, with their directions making an 135° angle, will be used for the study of the radiation reaction, non-linear Thomson scattering, electron beam cooling and other QED phenomena in the relativistic regime. The pump 10 PW Laser beam focused in a gas-jet will generate a plasma wakefield that accelerate electrons by self-injection. The probe 10PW Laser pulse has to be synchronized and focused on the electron bunch. In order to maximize the flux of gamma rays produced in this collision, for a given Laser field intensity, the transversal area of the electron beam at the collision point has to be smaller than the focus of the probe pulse. This work presents the calculation of electron beam emittance and angular divergence, versus the distance traveled by electron bunch in vacuum. A configuration of dipole permanent magnets is proposed for the study of energy distribution of electrons and positrons.
Ab initio calculation of the electronic absorption spectrum of liquid water
Energy Technology Data Exchange (ETDEWEB)
Martiniano, Hugo F. M. C.; Galamba, Nuno [Grupo de Física Matemática da Universidade de Lisboa, Av. Professor Gama Pinto 2, 1649-003 Lisboa (Portugal); Cabral, Benedito J. Costa, E-mail: ben@cii.fc.ul.pt [Grupo de Física Matemática da Universidade de Lisboa, Av. Professor Gama Pinto 2, 1649-003 Lisboa (Portugal); Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa (Portugal); Instituto de Física da Universidade de São Paulo, CP 66318, 05314-970 São Paulo, SP (Brazil)
2014-04-28
The electronic absorption spectrum of liquid water was investigated by coupling a one-body energy decomposition scheme to configurations generated by classical and Born-Oppenheimer Molecular Dynamics (BOMD). A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies in the liquid phase were calculated with the equation of motion coupled cluster with single and double excitations method. Molecular dynamics configurations were generated by different approaches. Classical MD were carried out with the TIP4P-Ew and AMOEBA force fields. The BLYP and BLYP-D3 exchange-correlation functionals were used in BOMD. Theoretical and experimental results for the electronic absorption spectrum of liquid water are in good agreement. Emphasis is placed on the relationship between the structure of liquid water predicted by the different models and the electronic absorption spectrum. The theoretical gas to liquid phase blue-shift of the peak positions of the electronic absorption spectrum is in good agreement with experiment. The overall shift is determined by a competition between the O–H stretching of the water monomer in liquid water that leads to a red-shift and polarization effects that induce a blue-shift. The results illustrate the importance of coupling many-body energy decomposition schemes to molecular dynamics configurations to carry out ab initio calculations of the electronic properties in liquid phase.
Electronic Structure Calculations for Heavy Elements: Radon (Z=86) and Francium (Z=87)
Koufos, Alexander; Papaconstantopoulos, Dimitrios
2010-03-01
Electronic structure calculations allow scientists to predict the properties of solids without the use of physical material. Although the ability to manipulate matter has improved dramatically within the past couple decades, some matter is still hard to study. Modern computers not only let us study this matter, but allow us to do it more quickly and just as accurately. The electronic structure of two rare and mostly unstudied elements, Radon (Z=86) and Francium (Z=87), has been calculated. The augmented plane wave (APW) method with local density approximation (LDA) functional as well as the linearized augmented plane wave (LAPW) method with both LDA and generalized gradient approximation (GGA) functionals were used to perform the calculations. Francium total energy calculations gave the fcc structure slightly below the bcc structure with a minimal energy difference of δE=0.33mRy. The difference found is consistent with other alkali metal total energy calculations which do not verify the bcc structure to be the ground state. Radon was predicted to be an insulator with a gap of 0.931 Ry similar to the other noble gases.
Energy Technology Data Exchange (ETDEWEB)
Abtew, Tesfaye A; Drabold, D A [Department of Physics and Astronomy, Ohio University, Athens, OH 45701-2979 (United States)
2004-11-10
In this paper we study electron dynamics and transport in models of amorphous silicon and amorphous silicon hydride. By integrating the time-dependent Kohn-Sham equation, we compute the time evolution of electron states near the gap, and study the spatial and spectral diffusion of these states due to lattice motion. We perform these calculations with a view to developing ab initio hopping transport methods. The techniques are implemented with the ab initio local basis code SIESTA, and may be applicable to molecular, biomolecular and other condensed matter systems.
Stability, electronic and thermodynamic properties of aluminene from first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Yuan, Junhui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Yu, Niannian [School of Science, Wuhan University of Technology, Wuhan, Hubei 430070 (China); Xue, Kanhao, E-mail: xkh@hust.edu.cn [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Miao, Xiangshui [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)
2017-07-01
Highlights: • We have predicted two NEW stable phases of atomic layer aluminum, buckled and 8-Pmmn aluminene. • We have revealed the electronic structures and bonding characteristics of aluminene. • Thermodynamic properties of aluminene were investigated based on phonon properties. - Abstract: Using first-principles calculations based on density functional theory (DFT), we have investigated the structure stability and electronic properties of both buckled and 8-Pmmn phase aluminene. Phonon dispersion analysis reveals that the buckled and 8-Pmmn aluminene are dynamically stable. The band structure shows that both the buckled and 8-Pmmn aluminene exhibit metallic behavior. Finally, the thermodynamic properties are investigated based on phonon properties.
Can Coulomb Sturmians Be Used as a Basis for N-Electron Molecular Calculations?
DEFF Research Database (Denmark)
Avery, John Scales; Avery, James Emil
2009-01-01
A method is proposed for using isoenergetic configurations formed from many-center Coulomb Sturmians as a basis for calculations on N-electron molecules. Such configurations are solutions to an approximate N-electron Schrödinger equation with a weighted potential, and they are thus closely...... analogous to the Goscinskian configurations that we have used previously to study atomic spectra. We show that when the method is applied to diatomic molecules, all of the relevant integrals are pure functions of the parameter s=kR, and therefore they can be evaluated once and for all and stored....
Energy Technology Data Exchange (ETDEWEB)
Kurova, N. V., E-mail: kurova_natasha@mail.ru; Burdov, V. A. [Lobachevskii Nizhni Novgorod State University (Russian Federation)
2013-12-15
The results of ab initio calculations of the electronic structure of Si nanocrystals doped with shallow donors (Li, P) are reported. It is shown that phosphorus introduces much more significant distortions into the electronic structure of the nanocrystal than lithium, which is due to the stronger central cell potential of the phosphorus ion. It is found that the Li-induced splitting of the ground state in the conduction band of the nanocrystal into the singlet, doublet, and triplet retains its inverse structure typical for bulk silicon.
Dai, Peng; Jiang, Nan; Tan, Ren-Xiang
2016-01-01
Elucidation of absolute configuration of chiral molecules including structurally complex natural products remains a challenging problem in organic chemistry. A reliable method for assigning the absolute stereostructure is to combine the experimental circular dichroism (CD) techniques such as electronic and vibrational CD (ECD and VCD), with quantum mechanics (QM) ECD and VCD calculations. The traditional QM methods as well as their continuing developments make them more applicable with accuracy. Taking some chiral natural products with diverse conformations as examples, this review describes the basic concepts and new developments of QM approaches for ECD and VCD calculations in solution and solid states.
Verification of EPA's " Preliminary remediation goals for radionuclides" (PRG) electronic calculator
Energy Technology Data Exchange (ETDEWEB)
Stagich, B. H. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
2017-03-29
The U.S. Environmental Protection Agency (EPA) requested an external, independent verification study of their “Preliminary Remediation Goals for Radionuclides” (PRG) electronic calculator. The calculator provides information on establishing PRGs for radionuclides at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) sites with radioactive contamination (Verification Study Charge, Background). These risk-based PRGs set concentration limits using carcinogenic toxicity values under specific exposure conditions (PRG User’s Guide, Section 1). The purpose of this verification study is to ascertain that the computer codes has no inherit numerical problems with obtaining solutions as well as to ensure that the equations are programmed correctly.
Valence electronic structure of the indene molecule: Experiment vs. GW calculations
Energy Technology Data Exchange (ETDEWEB)
Umari, P.; Stenuit, G. [CNR-IOM DEMOCRITOS Theory Elettra Group, Basovizza, Trieste (Italy); Castellarin-Cudia, C.; Feyer, V.; Di Santo, G.; Goldoni, A. [Sincrotrone Trieste S.C.p.A., Basovizza, Trieste (Italy); Borghetti, P.; Sangaletti, L. [Dipartimento di Matematica e Fisica, Universita Cattolica del Sacro Cuore, Brescia (Italy)
2011-04-15
We investigate the valence electronic properties in the gas phase of the indene molecule, which is one of the simplest polycyclic aromatic hydrocarbons, with photoemission spectroscopy using synchrotron light and through first-principles calculations using a many-body perturbation theory GW approach. We found an excellent agreement between theory and experiment. This allows us to assign to the peaks appearing in the photoemission spectrum the calculated molecular orbitals. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Directory of Open Access Journals (Sweden)
Yu Wang
2002-01-01
Full Text Available Abstract:We investigate a theoretical model of molecular metalwire constructed from linear polynuclear metal complexes. In particular we study the linear Crn metal complex and Cr molecular metalwire. The electron density distributions of the model nanowire and the linear Crn metal complexes, with n = 3, 5, and 7, are calculated by employing CRYSTAL98 package with topological analysis. The preliminary results indicate that the bonding types between any two neighboring Cr are all the same, namely the polarized open-shell interaction. The pattern of electron density distribution in metal complexes resembles that of the model Cr nanowire as the number of metal ions increases. The conductivity of the model Cr nanowire is also tested by performing the band structure calculation.
Multi-Center Electronic Structure Calculations for Plasma Equation of State
Energy Technology Data Exchange (ETDEWEB)
Wilson, B G; Johnson, D D; Alam, A
2010-12-14
We report on an approach for computing electronic structure utilizing solid-state multi-center scattering techniques, but generalized to finite temperatures to model plasmas. This approach has the advantage of handling mixtures at a fundamental level without the imposition of ad hoc continuum lowering models, and incorporates bonding and charge exchange, as well as multi-center effects in the calculation of the continuum density of states.
Electronic, optical, and thermodynamic properties of borophene from first-principle calculations
Peng, Bo; Zhang, Hao; Shao, Hezhu; Xu, Yuanfeng; Zhang, Rongjun; Zhu, Heyuan
2016-01-01
Borophene (two-dimensional boron sheet) is a new type of two-dimensional material, which was recently grown successfully on single crystal Ag substrates. In this paper, we investigate the electronic structure and bonding characteristics of borophene by first-principle calculations. The band structure of borophene shows highly anisotropic metallic behaviour. The obtained optical properties of borophene exhibit strong anisotropy as well. The combination of high optical transparency and high ele...
Energy Technology Data Exchange (ETDEWEB)
Kohn, S.; Weare, J.; Ong, E.; Baden, S.
1997-05-01
We have applied structured adaptive mesh refinement techniques to the solution of the LDA equations for electronic structure calculations. Local spatial refinement concentrates memory resources and numerical effort where it is most needed, near the atomic centers and in regions of rapidly varying charge density. The structured grid representation enables us to employ efficient iterative solver techniques such as conjugate gradient with FAC multigrid preconditioning. We have parallelized our solver using an object- oriented adaptive mesh refinement framework.
Schwerdtfeger, Christine A; Mazziotti, David A
2012-12-28
Treatment of two-electron excitations is a fundamental but computationally expensive part of ab initio calculations of many-electron correlation. In this paper we develop a low-rank spectral expansion of two-electron excitations for accelerated electronic-structure calculations. The spectral expansion differs from previous approaches by relying upon both (i) a sum of three expansions to increase the rank reduction of the tensor and (ii) a factorization of the tensor into geminal (rank-two) tensors rather than orbital (rank-one) tensors. We combine three spectral expansions from the three distinct forms of the two-electron reduced density matrix (2-RDM), (i) the two-particle (2)D, (ii) the two-hole (2)Q, and the (iii) particle-hole (2)G matrices, to produce a single spectral expansion with significantly accelerated convergence. While the resulting expansion is applicable to any quantum-chemistry calculation with two-particle excitation amplitudes, it is employed here in the parametric 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)]. The low-rank parametric 2-RDM method scales quartically with the basis-set size, but like its full-rank version it can capture multi-reference correlation effects that are difficult to treat efficiently by traditional single-reference wavefunction methods. Applications are made to computing potential energy curves of HF and triplet OH(+), equilibrium bond distances and frequencies, the HCN-HNC isomerization, and the energies of hydrocarbon chains. Computed 2-RDMs nearly satisfy necessary N-representability conditions. The low-rank spectral expansion has the potential to expand the applicability of the parametric 2-RDM method as well as other ab initio methods to large-scale molecular systems that are often only treatable by mean-field or density functional theories.
Atomistic calculation of electronic and optical properties of a single InAs quantum dots
Zielinski, M.; Korkusinski, M.; Sheng, W.; Hawrylak, P.
2008-03-01
We present an atomistic tight-binding (TB) theory of electronic structure and optical properties of a single self-assembled InAs quantum dot (SAD). In previous work an effective-bond-orbital model (EBOM) was used to calculate electron and hole states of the SAD. The strain distribution was calculated using the continuum elasticity theory and EBOM was coupled to the strain via the Bir-Pikus Hamiltonian. However, the properties of these multimillion-atom systems are influenced by the presence of crystal facets and the symmetry of underlying zinc-blende lattice. In current work we present a fully atomistic TB model, accounting for the atomistic symmetry, and extended to include d-orbitals for proper treatment of interband/intervalley couplings. Strain is included in the Hamiltonian via Slater-Koster rules and a generalized Harrison law, with the equilibrium positions of atoms calculated using the valence force field method. Coulomb matrix elements are found using the TB functions, and electronic properties of N confined excitons (N=1-6) are determined in the CI approach. Emission spectra of multiexcitons are also obtained. Comparison with the previous approach and the experimental results is presented.
Athanasiou, Christina; Vasilakaki, Sofia; Dellis, Dimitris; Cournia, Zoe
2017-11-01
Computer-aided drug design has become an integral part of drug discovery and development in the pharmaceutical and biotechnology industry, and is nowadays extensively used in the lead identification and lead optimization phases. The drug design data resource (D3R) organizes challenges against blinded experimental data to prospectively test computational methodologies as an opportunity for improved methods and algorithms to emerge. We participated in Grand Challenge 2 to predict the crystallographic poses of 36 Farnesoid X Receptor (FXR)-bound ligands and the relative binding affinities for two designated subsets of 18 and 15 FXR-bound ligands. Here, we present our methodology for pose and affinity predictions and its evaluation after the release of the experimental data. For predicting the crystallographic poses, we used docking and physics-based pose prediction methods guided by the binding poses of native ligands. For FXR ligands with known chemotypes in the PDB, we accurately predicted their binding modes, while for those with unknown chemotypes the predictions were more challenging. Our group ranked #1st (based on the median RMSD) out of 46 groups, which submitted complete entries for the binding pose prediction challenge. For the relative binding affinity prediction challenge, we performed free energy perturbation (FEP) calculations coupled with molecular dynamics (MD) simulations. FEP/MD calculations displayed a high success rate in identifying compounds with better or worse binding affinity than the reference (parent) compound. Our studies suggest that when ligands with chemical precedent are available in the literature, binding pose predictions using docking and physics-based methods are reliable; however, predictions are challenging for ligands with completely unknown chemotypes. We also show that FEP/MD calculations hold predictive value and can nowadays be used in a high throughput mode in a lead optimization project provided that crystal structures of
Athanasiou, Christina; Vasilakaki, Sofia; Dellis, Dimitris; Cournia, Zoe
2018-01-01
Computer-aided drug design has become an integral part of drug discovery and development in the pharmaceutical and biotechnology industry, and is nowadays extensively used in the lead identification and lead optimization phases. The drug design data resource (D3R) organizes challenges against blinded experimental data to prospectively test computational methodologies as an opportunity for improved methods and algorithms to emerge. We participated in Grand Challenge 2 to predict the crystallographic poses of 36 Farnesoid X Receptor (FXR)-bound ligands and the relative binding affinities for two designated subsets of 18 and 15 FXR-bound ligands. Here, we present our methodology for pose and affinity predictions and its evaluation after the release of the experimental data. For predicting the crystallographic poses, we used docking and physics-based pose prediction methods guided by the binding poses of native ligands. For FXR ligands with known chemotypes in the PDB, we accurately predicted their binding modes, while for those with unknown chemotypes the predictions were more challenging. Our group ranked #1st (based on the median RMSD) out of 46 groups, which submitted complete entries for the binding pose prediction challenge. For the relative binding affinity prediction challenge, we performed free energy perturbation (FEP) calculations coupled with molecular dynamics (MD) simulations. FEP/MD calculations displayed a high success rate in identifying compounds with better or worse binding affinity than the reference (parent) compound. Our studies suggest that when ligands with chemical precedent are available in the literature, binding pose predictions using docking and physics-based methods are reliable; however, predictions are challenging for ligands with completely unknown chemotypes. We also show that FEP/MD calculations hold predictive value and can nowadays be used in a high throughput mode in a lead optimization project provided that crystal structures of
Linear scaling 3D fragment method for large-scale electronic structure calculations
Energy Technology Data Exchange (ETDEWEB)
Wang, Lin-Wang; Wang, Lin-Wang; Lee, Byounghak; Shan, HongZhang; Zhao, Zhengji; Meza, Juan; Strohmaier, Erich; Bailey, David
2008-07-11
We present a new linearly scaling three-dimensional fragment (LS3DF) method for large scale ab initio electronic structure calculations. LS3DF is based on a divide-and-conquer approach, which incorporates a novel patching scheme that effectively cancels out the artificial boundary effects due to the subdivision of the system. As a consequence, the LS3DF program yields essentially the same results as direct density functional theory (DFT) calculations. The fragments of the LS3DF algorithm can be calculated separately with different groups of processors. This leads to almost perfect parallelization on tens of thousands of processors. After code optimization, we were able to achieve 35.1 Tflop/s, which is 39% of the theoretical speed on 17,280 Cray XT4 processor cores. Our 13,824-atom ZnTeO alloy calculation runs 400 times faster than a direct DFT calculation, even presuming that the direct DFT calculation can scale well up to 17,280 processor cores. These results demonstrate the applicability of the LS3DF method to material simulations, the advantage of using linearly scaling algorithms over conventional O(N{sup 3}) methods, and the potential for petascale computation using the LS3DF method.
Method for calculating ionic and electronic defect concentrations in y-stabilised zirconia
Energy Technology Data Exchange (ETDEWEB)
Poulsen, F.W. [Risoe National Lab., Materials Research Dept., Roskilde (Denmark)
1997-10-01
A numerical (trial and error) method for calculation of concentration of ions, vacancies and ionic and electronic defects in solids (Brouwer-type diagrams) is presented. No approximations or truncations of the set of equations describing the chemistry for the various defect regions are used. Doped zirconia and doped thoria with simultaneous presence of protonic and electronic defects are taken as examples: 7 concentrations as function of oxygen partial pressure and/or water vapour partial pressure are determined. Realistic values for the equilibrium constants for equilibration with oxygen gas and water vapour, as well as for the internal equilibrium between holes and electrons were taken from the literature. The present mathematical method is versatile - it has also been employed by the author to treat more complex systems, such as perovskite structure oxides with over- and under-stoichiometry in oxygen, cation vacancies and simultaneous presence of protons. (au) 6 refs.
Quantum-mechanical calculations of cross sections for electron collisions with atoms and molecules
Bartschat, Klaus; Zatsarinny, Oleg
2016-01-01
An overview of quantum-mechanical methods to generate cross-section data for electron collisions with atoms and molecules is presented. Particular emphasis is placed on the time-independent close-coupling approach, since it is particularly suitable for low-energy collisions and also allows for systematic improvements as well as uncertainty estimates. The basic ideas are illustrated with examples for electron collisions with argon atoms and methane. For many atomic systems, such as e-Ar collisions, highly reliable cross sections can now be computed with quantified uncertainties. On the other hand, while electron collision calculations with molecules do provide key input data for plasma models, the methods and computer codes presently used require further development to make these inputs robust.
Energy Technology Data Exchange (ETDEWEB)
Tikhonov, E. V., E-mail: tikhonov@mig.phys.msu.ru [Moscow State University (Russian Federation); Uspenskii, Yu. A. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Khokhlov, D. R. [Moscow State University (Russian Federation)
2015-06-15
A quasiparticle electronic spectrum belongs to the characteristics of nanoobjects that are most important for applications. The following methods of calculating the electronic spectrum are analyzed: the Kohn-Sham equations of the density functional theory (DFT), the hybrid functional method, the GW approximation, and the Lehmann approximation used in the spectral representation of one-electron Green’s function. The results of these approaches are compared with the data of photoemission measurements of benzene, PTCDA, and phthalocyanine (CuPc, H{sub 2}Pc, FePc, PtPc) molecules, which are typical representatives of organic molecular semiconductors (OMS). This comparison demonstrates that the Kohn-Sham equations of DFT incorrectly reproduce the electronic spectrum of OMS. The hybrid functional method correctly describes the spectrum of the valence and conduction bands; however, the HOMO-LUMO gap width is significantly underestimated. The correct gap width is obtained in both the GW approximation and the Lehmann approach, and the total energy in this approach can be calculated in the local density approximation of DFT.
Calculating the electron temperature in the lightning channel by continuous spectrum
Xiangcheng, DONG; Jianhong, CHEN; Xiufang, WEI; Ping, YUAN
2017-12-01
Based on the theory of plasma continuous radiation, the relationship between the emission intensity of bremsstrahlung and recombination radiation and the plasma electron temperature is obtained. During the development process of a return stroke of ground flash, the intensity of continuous radiation spectrum is separated on the basis of the spectrums with obviously different luminous intensity at two moments. The electron temperature of the lightning discharge channel is obtained through the curve fitting of the continuous spectrum intensity. It is found that electron temperature increases with the increase of wavelength and begins to reduce after the peak. The peak temperature of the two spectra is close to 25 000 K. To be compared with the result of discrete spectrum, the electron temperature is fitted by the O I line and N II line of the spectrum respectively. The comparison shows that the high temperature value is in good agreement with the temperature of the lightning core current channel obtained from the ion line information, and the low temperature at the high band closes to the calculation result of the atomic line, at a low band is lower than the calculation of the atomic line, which reflects the temperature of the luminous channel of the outer corona.
Yalçın, Şerife Pınar; Ceylan, Ümit; Sönmez, Mehmet; Hacıyusufoğlu, Mehmet Emin; Karavelioğlu, Hatice
2017-11-01
In this study, Cu(II) complex, C52H40CuN6O10, was synthesized and the molecular structure was characterized by experimental Electron Paramagnetic Resonance (EPR), vibrational frequencies, absorption wavelengths and compared with theoretical methods. The molecular geometry was calculated and optimized by using Gaussian 09 software and DFT-B3LYP and B3PW91 methods with the LanL2DZ basis sets in ground state. The theoretical vibrational frequencies, was optimized geometric parameters such as bond lengths, bond angles and torsion angles and absorption wavelengths, NBO, FMO analysis, HOMO-LUMO energy and nonlinear optical properties, molecular electrostatic potential, spin density have been calculated via quantum chemical methods. Theoretically calculated data were compared with experimentally measured data. Also, the results obtained by using the two basis sets were compared with each other.
Phase transition and electronic properties of SbI3: First-principles calculations
Sun, Xiao-Xiao; Li, Cong; Hou, Qing-Yu; Zhang, Yue
2017-06-01
We have performed the first-principles pseudopotential calculations to investigate the structural phase transition and electronic properties of SbI3 considering several possible phases as a function of pressure from 0 GPa to 100 GPa. Our calculations show that this material undertakes a structural transformation from the R-3 phase to high-pressure P21/c phase at about 6.5 GPa with a relative volume collapse of 4.3%. We also have investigated the elastic properties and energy band structure of SbI3 under hydrostatic pressure. The calculation suggests that the R-3 phase is a semiconductor with an indirect band gap of about 2.16 eV at 0 Gpa. Under the influence of pressure, we have found that high-pressure P21/c phase has transformed to metal at about 55 GPa.
Effect of tensile strain on the electronic structure of Ge: A first-principles calculation
Energy Technology Data Exchange (ETDEWEB)
Liu, Li [Key Laboratory for Microstructures and Institute of Materials Science, Shanghai University, Shanghai 200072 (China); State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Zhang, Miao; Di, Zengfeng, E-mail: zfdi@mail.sim.ac.cn, E-mail: shijin.zhao@shu.edu.cn [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Hu, Lijuan; Zhao, Shi-Jin, E-mail: zfdi@mail.sim.ac.cn, E-mail: shijin.zhao@shu.edu.cn [Key Laboratory for Microstructures and Institute of Materials Science, Shanghai University, Shanghai 200072 (China)
2014-09-21
Taking the change of L-point conduction band valley degeneracy under strain into consideration, we investigate the effect of biaxially tensile strain (parallel to the (001), (110), and (111) planes) and uniaxially tensile strain (along the [001], [110], and [111] directions) on the electronic structure of Ge using density functional theory calculations. Our calculation shows that biaxial tension parallel to (001) is the most efficient way to transform Ge into a direct bandgap material among all tensile strains considered. [111]-tension is the best choice among all uniaxial approaches for an indirect- to direct-bandgap transition of Ge. The calculation results, which are further elaborated by bond-orbital approximation, provide a useful guidance on the optical applications of Ge through strain engineering.
Wang, Neng-Ping
2011-01-01
I present a method to calculate the ballistic transport properties of atomic-scale structures under bias. The electronic structure of the system is calculated using the Kohn-Sham scheme of density functional theory (DFT). The DFT eigenvectors are then transformed into a set of maximally localized Wannier functions (MLWFs) [N. Marzari and D. Vanderbilt, Phys. Rev. B 56 (1997) 12847]. The MLWFs are used as a minimal basis set to obtain the Hamitonian matrices of the scattering region and the adjacent leads, which are needed for transport calculation using the nonequilibrium Green's function formalism. The coupling of the scattering region to the semi-infinite leads is described by the self-energies of the leads. Using the nonequilibrium Green's function method, one calculates self-consistently the charge distribution of the system under bias and evaluates the transmission and current through the system. To solve the Poisson equation within the scheme of MLWFs I introduce a computationally efficient method. The method is applied to a molecular hydrogen contact in two transition metal monatomic wires (Cu and Pt). It is found that for Pt the I-V characteristics is approximately linear dependence, however, for Cu the I-V characteristics manifests a linear dependence at low bias voltages and exhibits apparent nonlinearity at higher bias voltages. I have also calculated the transmission in the zero bias voltage limit for a single CO molecule adsorbed on Cu and Pt monatomic wires. While a chemical scissor effect occurs for the Cu monatomic wire with an adsorbed CO molecule, it is absent for the Pt monatomic wire due to the contribution of d-orbitals at the Fermi energy.
Electron-molecule collision calculations using the R-matrix method
Energy Technology Data Exchange (ETDEWEB)
Tennyson, Jonathan, E-mail: j.tennyson@ucl.ac.u [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)
2010-06-15
The R-matrix method is an embedding procedure which is based on the division of space into an inner region where the physics is complicated and an outer region for which greatly simplified equations can be solved. The method developed out of nuclear physics, where the effects of the inner region were simply parametrized, into atomic and molecular physics, where the full problem can be formulated and hopefully solved ab initio. In atomic physics R-matrix based procedures are the method of choice for the ab initio calculation of electron collision parameters. There has been a number of R-matrix procedures developed to treat the low-energy electron-molecule collision problem or particular aspects of this problem. These methods have been extended to both positron physics and the R-matrix treatment of vibrational motion. The physical basis of the R-matrix method as well as its theoretical formulation are presented. Various electron scattering models within an R-matrix formulation including static exchange, static exchange plus polarization and close coupling are described with reference to various computational implementations of the method; these are compared to similar models used within other scattering methods. The need for a balanced treatment of the target and continuum wave functions is emphasised. Extensions of close-coupling based models into the intermediate energy regime using pseudo-states is discussed, as is the adaptation of R-matrix methods to problems involving photons. The numerical realisation of the R-matrix method is based on the adaptation of quantum chemistry codes in the inner region and asymptotic electron-atom scattering programs in the outer region. Use of bound state codes in scattering calculations raises issues involving continuum basis sets, appropriate orbitals, integral evaluation, orthogonalization, Hamiltonian construction and diagonalization which need to be addressed. The algorithms developed to resolve these issues are described as
Schiemann, Olav; Fritscher, Jörg; Kisseleva, Natalja; Sigurdsson, Snorri Th; Prisner, Thomas F
2003-10-06
Electron paramagnetic resonance spectroscopy and density functional theory methods were used to study the structure of a single, high-affinity Mn(II) binding site in the hammerhead ribozyme. This binding site exhibits a dissociation constant Ke of 4.4 microM in buffer solutions containing 1 M NaCl, as shown by titrations monitored by continuous wave (cw) EPR. A combination of electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) experiments revealed that the paramagnetic manganese(II) ion in this binding site is coupled to a single nitrogen atom with a quadrupole coupling constant kappa of 0.7 MHz, an asymmetry parameter eta of 0.4, and an isotropic hyperfine coupling constant of Aiso(14N)=2.3 MHz. All three EPR parameters are sensitive to the arrangement of the Mn(II) ligand sphere and can therefore be used to determine the structure of the binding site. A possible location for this binding site may be at the G10.1, A9 site found to be occupied by Mn(II) in crystals (MacKay et al., Nature 1994, 372, 68 and Scott et al., Science 1996, 274, 2065). To determine whether the structure of the binding site is the same in frozen solution, we performed DFT calculations for the EPR parameters, based on the structure of the Mn(II) site in the crystal. Computations with the BHPW91 density function in combination with a 9s7p4d basis set for the manganese(II) center and the Iglo-II basis set for all other atoms yielded values of kappa(14N)=+0.80 MHz, eta=0.324, and Aiso(14N)=+2.7 MHz, in excellent agreement with the experimentally obtained EPR parameters, which suggests that the binding site found in the crystal and in frozen solution are the same. In addition, we demonstrated by EPR that Mn(II) is released from this site upon binding of the aminoglycoside antibiotic neomycin B (Kd=1.2 microM) to the hammerhead ribozyme. Neomycin B has previously been shown to inhibit the catalytic activity of this ribozyme (Uhlenbeck et al., Biochemistry
Energy Technology Data Exchange (ETDEWEB)
Erhart, Paul [Applied Physics, Chalmers University of Technology, Gothenburg (Sweden); Lawrence Livermore National Laboratory, Livermore, California (United States); Aaberg, Daniel; Sadigh, Babak [Lawrence Livermore National Laboratory, Livermore, California (United States)
2012-07-01
Rare-earth based scintillators represent a challenging class of scintillator materials due to pronounced spin-orbit coupling and subtle interactions between d and f states that cannot be reproduced by standard electronic structure methods such as density functional theory. In this contribution we present a detailed investigation of the electronic band structure of LaBr{sub 3} using the quasi-p article self-consistent GW (scGW) method. This parameter-free approach is shown to yield an excellent description of the electronic structure of LaBr{sub 3}. Specifically we reproduce the correct level ordering and spacing of the 4f and 5d states, which are inverted with respect to the free La atom, the band gap as well as the spin-orbit splitting of La-derived states. We furthermore present electronic structure calculations using G{sub 0}W{sub 0} for the important scintillator material SrI{sub 2}. We explicitly take into account spin-orbit coupling at all levels of the theory. Our results demonstrate the applicability and reliability of the scGW approach for rare-earth halides. They furthermore provide an excellent starting point for investigating the electronic structure of rare-earth dopants such as Ce and Er.
Calculation of properties of the electron-hole liquid in uniaxially stressed Ge and Si
Energy Technology Data Exchange (ETDEWEB)
Kelso, S.M.
1982-06-15
We present a detailed theoretical study of the stress dependence of properties of the electron-hole liquid, both at zero and finite temperatures, in <111>-stressed Ge and <100>-stressed Si. These properties include the ground-state equilibrium density, pair energy, electron and hole Fermi energies, sign of the electron-hole drop charge, luminescence linewidth, and liquid compressibility. The results are compared at T = 0 to the calculations of Kirczenow and Singwi and at Troughly-equal2 K to the available data. We discuss the possibility of a phase transition associated with the depopulation of the upper electron valleys in Ge. We also discuss methods of extrapolating from finite to infinite stress. The importance of the nonparabolicity of the valence bands is emphasized throughout. We discuss ranges of validity for a low-temperature expansion of the free energy. Results are presented for the systematic low-temperature variation of the liquid density, Fermi energy, and chemical potential and for the critical temperature and density. These theoretical results are found to be in reasonably good agreement with available data. Finally, we discuss scaling relations for combinations of electron-hole--liquid properties.
Linearly Scaling 3D Fragment Method for Large-Scale Electronic Structure Calculations
Energy Technology Data Exchange (ETDEWEB)
Wang, Lin-Wang; Lee, Byounghak; Shan, Hongzhang; Zhao, Zhengji; Meza, Juan; Strohmaier, Erich; Bailey, David H.
2008-07-01
We present a new linearly scaling three-dimensional fragment (LS3DF) method for large scale ab initio electronic structure calculations. LS3DF is based on a divide-and-conquer approach, which incorporates a novel patching scheme that effectively cancels out the artificial boundary effects due to the subdivision of the system. As a consequence, the LS3DF program yields essentially the same results as direct density functional theory (DFT) calculations. The fragments of the LS3DF algorithm can be calculated separately with different groups of processors. This leads to almost perfect parallelization on tens of thousands of processors. After code optimization, we were able to achieve 35.1 Tflop/s, which is 39percent of the theoretical speed on 17,280 Cray XT4 processor cores. Our 13,824-atom ZnTeO alloy calculation runs 400 times faster than a direct DFTcalculation, even presuming that the direct DFT calculation can scale well up to 17,280 processor cores. These results demonstrate the applicability of the LS3DF method to material simulations, the advantage of using linearly scaling algorithms over conventional O(N3) methods, and the potential for petascale computation using the LS3DF method.
Li, Qianshu; Li, Guoliang; Xu, Wenguo; Xie, Yaoming; Schaefer, Henry F
2002-02-15
A systematic investigation of Ge2Fn/Ge2Fn- systems was carried out with five density functional theory (DFT) methods in conjunction with DZP++ basis sets. For each compound various structures, including minima, transition states and other energetically low lying stationary points, were optimized. The geometries and relative energies are discussed and compared. Adiabatic electron affinities, vertical electron affinities and anion vertical detachment energies are reported. Three types of dissociation energies pertaining to the global minima for each compound are reported. The theoretical predictions are in good agreement with the limited available experimental results. Many unusual structural features are predicted for these systems. Neutral Ge2F is predicted to have a bridged C2v structure, while its anion is very floppy, with the bridged structure very slightly favoured. The Ge2F2 molecule is predicted to have the butterfly structure known from experiment for Si2H2, while the Ge2F3- ion has a trans-bent structure. Ge2F3 is predicted to have an unprecedented FGe-F-GeF structure with no Ge-Ge bond, while its anion has a somewhat more conventional monobridged structure, analogous to that of the nonclassical vinyl cation. Neutral Ge2F4 has a dibridged structure of C2h symmetry, while its anion has a trans-bent structure with a very long Ge-Ge bond. The Ge2F5 molecule is doubly bridged and has no Ge-Ge bond, while the anion is of the type F2Ge-F-GeF2, again with no Ge-Ge bond. Ge2F6 has the anticipated ethane structure, as does its anion, but with a very long Ge-Ge bond. The adiabatic electron affinities (EAad) are predicted to be 2.12 (Ge2F), 2.03 (Ge2F2), 2.02 (Ge2F3), 1.64 (Ge2F4), 4.57 (Ge2F5), and 2.66 eV (Ge2F6), respectively, by the BHLYP method, which is regarded as the best method in the present paper for predicting EAs. Comparisons with the analogous C2Fn and Si2Fn systems reveals some interesting trends and differences. For example, while C2F6 will not
First-principles calculations of atomic and electronic properties of ZnO nanostructures
Energy Technology Data Exchange (ETDEWEB)
Xu, H.; Fan, W.; Fang, D. [Nano-organic Photoelectronic Laboratory, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing (China); Graduate University of Chinese Academy of Sciences, Beijing (China); Rosa, A.L.; Frauenheim, T. [BCCMS, University of Bremen (Germany); Zhang, R.Q. [Center of Super-Diamond and Advanced Films (COSDAF) and Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR (China)
2010-10-15
We employ density-functional theory within the generalized-gradient approximation to investigate the formation energies and atomic and electronic structure of ZnO nanowires and nanotubes (NTs). We find that relaxations on the facets of the bare wires are very similar to those in nonpolar (10 anti 10) surfaces and play an important role in stabilizing the nanowires. All bare wires are found to be semiconducting, with band gaps larger than that in bulk ZnO. We further investigated hydrogen and water adsorption on ZnO nanowires. We find that the electronic structure of ZnO nanowires can be tuned by hydrogen adsorption and that adsorption of water leads to dissociation of a half-monolayer. Next, the stability of ZnO NTs has been investigated. We show that multiwall NTs are more stable than single-walled tubes. Finally, point defects in ZnO NTs have been investigated using spin-polarized calculations. All calculations were shown to introduce defect levels in the band gap, thus changing the electronic structure of the NTs drastically. (Abstract Copyright [2010], Wiley Periodicals, Inc.)
Electronic and magnetic properties of Mn-doped ZnO: Total-energy calculations
Energy Technology Data Exchange (ETDEWEB)
AlGhamdi, Ghadah S [King Abdulaziz University Physics Department Faculty of Science PO Box 80203 Jeddah 21589 (Saudi Arabia); AlZahrani, A.Z., E-mail: azalzahrani@kau.edu.sa [King Abdulaziz University Physics Department Faculty of Science PO Box 80203 Jeddah 21589 (Saudi Arabia)
2012-10-01
Based on the spin generalized gradient approximation ({sigma}GGA) of the density functional theory (DFT), the structural, magnetic, and electronic properties of Mn-doped ZnO structure have thoroughly been investigated. It is found that the Mn atom prefers to substitute one of the Zn atoms, producing the energetically most stable configuration for the Mn-doped ZnO structure. Employing the Hubbard potential within the calculations suggests various changes and modifications to the structural, magnetic and electronic properties of the Mn-doped ZnO. Our calculations reveal that the local magnetic moment at the Mn site using the ordinary {sigma}GGA functional is 4.84 {mu}{sub B}/Mn, which is smaller than that evaluated by including the Hubbard potential of 5.04 {mu}{sub B}/Mn. Overall, the electronic band structure of the system, within the {sigma}GGA+U, is half-metallic, with metallic nature for the majority state and semiconducting nature for the minority state. Simulated scanning tunneling microscopy (STM) images for both unoccupied and occupied states indicate siginficant brightness on both Zn and Mn atoms and much brighter protrusions around the O atoms, respectively.
Lee, Jihang; Kioupakis, Emmanouil; Lu, Wei
2014-03-01
Tantalum oxide has been extensively studied due to its attractive properties as dielectric films, anti-reflection coatings, and resistive switching memory. Although various crystalline structures of tantalum pentoxide (Ta2O5) have been reported, the structural and electronic/optical properties still remain a controversial issue. We investigate the electronic and optical properties of crystalline and amorphous Ta2O5 structures using first-principles calculations in the GW approximation. The calculated band gaps of the crystalline structures are too small to explain the experimental measurements. The amorphous structure exhibits a strong exciton binding energy and an optical band gap (~ 4eV) similar to experiment. We determine the atomic orbitals that form the conduction band of each polymorph and analyze the dependence of the band gap on the atomic geometry. Our results establish the connection between the underlying structure and the electronic and optical properties of Ta2O5. This work was supported in part by the AFOSR through MURI grant FA9550-12-1-0038. Jihang Lee is supported in part by Kwanjeong Scholarship. Computational resources were provided by the DOE NERSC facility.
Adjoint affine fusion and tadpoles
Energy Technology Data Exchange (ETDEWEB)
Urichuk, Andrew, E-mail: andrew.urichuk@uleth.ca [Physics and Astronomy Department, University of Lethbridge, Lethbridge, Alberta T1K 3M4 (Canada); Walton, Mark A., E-mail: walton@uleth.ca [Physics and Astronomy Department, University of Lethbridge, Lethbridge, Alberta T1K 3M4 (Canada); International School for Advanced Studies (SISSA), via Bonomea 265, 34136 Trieste (Italy)
2016-06-15
We study affine fusion with the adjoint representation. For simple Lie algebras, elementary and universal formulas determine the decomposition of a tensor product of an integrable highest-weight representation with the adjoint representation. Using the (refined) affine depth rule, we prove that equally striking results apply to adjoint affine fusion. For diagonal fusion, a coefficient equals the number of nonzero Dynkin labels of the relevant affine highest weight, minus 1. A nice lattice-polytope interpretation follows and allows the straightforward calculation of the genus-1 1-point adjoint Verlinde dimension, the adjoint affine fusion tadpole. Explicit formulas, (piecewise) polynomial in the level, are written for the adjoint tadpoles of all classical Lie algebras. We show that off-diagonal adjoint affine fusion is obtained from the corresponding tensor product by simply dropping non-dominant representations.
A deterministic partial differential equation model for dose calculation in electron radiotherapy.
Duclous, R; Dubroca, B; Frank, M
2010-07-07
High-energy ionizing radiation is a prominent modality for the treatment of many cancers. The approaches to electron dose calculation can be categorized into semi-empirical models (e.g. Fermi-Eyges, convolution-superposition) and probabilistic methods (e.g.Monte Carlo). A third approach to dose calculation has only recently attracted attention in the medical physics community. This approach is based on the deterministic kinetic equations of radiative transfer. We derive a macroscopic partial differential equation model for electron transport in tissue. This model involves an angular closure in the phase space. It is exact for the free streaming and the isotropic regime. We solve it numerically by a newly developed HLLC scheme based on Berthon et al (2007 J. Sci. Comput. 31 347-89) that exactly preserves the key properties of the analytical solution on the discrete level. We discuss several test cases taken from the medical physics literature. A test case with an academic Henyey-Greenstein scattering kernel is considered. We compare our model to a benchmark discrete ordinate solution. A simplified model of electron interactions with tissue is employed to compute the dose of an electron beam in a water phantom, and a case of irradiation of the vertebral column. Here our model is compared to the PENELOPE Monte Carlo code. In the academic example, the fluences computed with the new model and a benchmark result differ by less than 1%. The depths at half maximum differ by less than 0.6%. In the two comparisons with Monte Carlo, our model gives qualitatively reasonable dose distributions. Due to the crude interaction model, these so far do not have the accuracy needed in clinical practice. However, the new model has a computational cost that is less than one-tenth of the cost of a Monte Carlo simulation. In addition, simulations can be set up in a similar way as a Monte Carlo simulation. If more detailed effects such as coupled electron-photon transport, bremsstrahlung
Hoke, Eric T.
2012-05-21
Understanding the stability and degradation mechanisms of organic solar materials is critically important to achieving long device lifetimes. Here, an investigation of the photodegradation of polymer:fullerene blend fi lms exposed to ambient conditions for a variety of polymer and fullerene derivative combinations is presented. Despite the wide range in polymer stabilities to photodegradation, the rate of irreversible polymer photobleaching in blend fi lms is found to consistently and dramatically increase with decreasing electron affi nity of the fullerene derivative. Furthermore, blends containing fullerenes with the smallest electron affi nities photobleached at a faster rate than fi lms of the pure polymer. These observations can be explained by a mechanism where both the polymer and fullerene donate photogenerated electrons to diatomic oxygen to form the superoxide radical anion which degrades the polymer. © 2012 WILEY-VCH Verlag GmbH & Co.
Sato, Fumitoshi; Yoshihiro, Tamotsu; Okazaki, Isao; Kashiwagi, Hiroshi
1999-09-01
An all-electron calculation of the antihypertensive and antiviral protein BDS-I from the sea anemone Anemonia sulcata was carried out using the density functional method based on Gaussian-type orbitals with workstations. Our computer program ProteinDF coded by the object-oriented language C++, was originally designed for all-electron calculations of proteins and controlled in parallel with high efficiency. The numbers of residues, atoms, orbitals and auxiliary functions of the calculated protein were 43, 629, 3615 and 6545, respectively. This Letter reports timing data of the computation and some calculated electronic properties. Our program will open the door for advanced studies of larger proteins.
First-principles calculations of BC{sub 4}N nanostructures: stability and electronic structure
Energy Technology Data Exchange (ETDEWEB)
Freitas, A.; Azevedo, S. [Universidade Federal da Paraiba, CCEN, Departamento de Fisica, Joao Pessoa, PB (Brazil); Machado, M. [Universidade Federal de Pelotas, Departamento de Fisica, Pelotas, RS (Brazil); Kaschny, J.R. [Instituto Federal da Bahia-Campus Vitoria da Conquista, Vitoria da Conquista, BA (Brazil)
2012-07-15
In this work, we apply first-principles methods to investigate the stability and electronic structure of BC{sub 4}N nanostructures which were constructed from hexagonal graphite layers where substitutional nitrogen and boron atoms are placed at specific sites. These layers were rolled up to form zigzag and armchair nanotubes, with diameters varying from 7 to 12 A, or cut and bent to form nanocones, with 60 and 120 disclination angles. The calculation results indicate that the most stable structures are the ones which maximize the number of B-N and C-C bonds. It is found that the zigzag nanotubes are more stable than the armchair ones, where the strain energy decreases with increasing tube diameter D, following a 1/D {sup 2} law. The results show that the 60 disclination nanocones are the most stable ones. Additionally, the calculated electronic properties indicate a semiconducting behavior for all calculated structures, which is intermediate to the typical behaviors found for hexagonal boron nitride and graphene. (orig.)
Electronic Structure of Cu(tmdt2 Studied with First-Principles Calculations
Directory of Open Access Journals (Sweden)
Kiyoyuki Terakura
2012-08-01
Full Text Available We have studied the electronic structure of Cu(tmdt2, a material related to single-component molecular conductors, by first-principles calculations. The total energy calculations for several different magnetic configurations show that there is strong antiferromagnetic (AFM exchange coupling along the crystal a-axis. The electronic structures are analyzed in terms of the molecular orbitals near the Fermi level of isolated Cu(tmdt2 molecule. This analysis reveals that the system is characterized by the half-filled pdσ(− band whose intermolecular hopping integrals have strong one-dimensionality along the crystal a-axis. As the exchange splitting of the band is larger than the band width, the basic mechanism of the AFM exchange coupling is the superexchange. It will also be shown that two more ligand orbitals which are fairly insensitive to magnetism are located near the Fermi level. Because of the presence of these orbitals, the present calculation predicts that Cu(tmdt2 is metallic even in its AFM state, being inconsistent with the available experiment. Some comments will be made on the difference between Cu(tmdt2 and Cu(dmdt2.
Energy Technology Data Exchange (ETDEWEB)
Akdim, Brahim, E-mail: brahim.akdim.ctr@us.af.mil, E-mail: ruth.pachter@us.af.mil [Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433 (United States); General Dynamics Information Technology, Inc., 500 Springfield Pike, Dayton, Ohio 454331 (United States); Pachter, Ruth, E-mail: brahim.akdim.ctr@us.af.mil, E-mail: ruth.pachter@us.af.mil; Naik, Rajesh R. [Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433 (United States)
2015-05-04
In this letter, we report on the evaluation of diphenylalanine (FF), dityrosine (YY), and phenylalanine-tryptophan (FW) self-assembled peptide nanotube structures for electronics and photonics applications. Realistic bulk peptide nanotube material models were used in density functional theory calculations to mimic the well-ordered tubular nanostructures. Importantly, validated functionals were applied, specifically by using a London dispersion correction to model intertube interactions and a range-separated hybrid functional for accurate bandgap calculations. Bandgaps were found consistent with available experimental data for FF, and also corroborate the higher conductance reported for FW in comparison to FF peptide nanotubes. Interestingly, the predicted bandgap for the YY tubular nanostructure was found to be slightly higher than that of FW, suggesting higher conductance as well. In addition, the band structure calculations along the high symmetry line of nanotube axis revealed a direct bandgap for FF. The results enhance our understanding of the electronic properties of these material systems and will pave the way into their application in devices.
Energy Technology Data Exchange (ETDEWEB)
Bronisz, K. [Department of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan (Poland); Ostafin, M. [Department of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan (Poland)], E-mail: ostifnqr@amu.edu.pl; Poleshchuk, O. Kh. [Department of Chemistry, Tomsk Pedagogical University, Komsomolskii 75, 634041 Tomsk (Russian Federation); Mielcarek, J. [Faculty of Pharmacy, University of Medical Sciences, Grunwaldzka 6, 60-780 Poznan (Poland); Nogaj, B. [Department of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan (Poland)
2006-11-08
Selected derivatives of 1,4-benzodiazepine: lorazepam, lormetazepam, oxazepam and temazepam, used as active substances in anxiolytic drugs, have been studied by {sup 35}Cl NQR method in order to find the correlation between electronic structure and biological activity. The {sup 35}Cl NQR resonance frequencies ({nu} {sub Q}) measured at 77 K have been correlated with the following parameters characterising their biological activity: biological half-life period (t {sub 0.5}), affinity to benzodiazepine receptor (IC{sub 50}) and mean dose equivalent. The results of experimental study of some benzodiazepine derivatives by nuclear quadrupole resonance of {sup 35}Cl nuclei are compared with theoretical results based on DFT calculations which were carried out by means of Gaussian'98 W software.
DEFF Research Database (Denmark)
Shim, Irene; Kingcade, Joseph E. , Jr.; Gingerich, Karl A.
1986-01-01
In the present work we present all-electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of six electronic states of the PdGe molecule. The molecule is predicted to have a 3Pi ground state and two low-lying excited states 3Sigma− and 1Sigma+. The electronic structure...
Beroza, P; Fredkin, D R; Okamura, M Y; Feher, G
1995-01-01
The titration of amino acids and the energetics of electron transfer from the primary electron acceptor (QA) to the secondary electron acceptor (QB) in the photosynthetic reaction center of Rhodobacter sphaeroides are calculated using a continuum electrostatic model. Strong electrostatic interactions between titrating sites give rise to complex titration curves. Glu L212 is calculated to have an anomalously broad titration curve, which explains the seemingly contradictory experimental results...
DEFF Research Database (Denmark)
Romero, N. A.; Glinsvad, Christian; Larsen, Ask Hjorth
2013-01-01
Density function theory (DFT) is the most widely employed electronic structure method because of its favorable scaling with system size and accuracy for a broad range of molecular and condensed-phase systems. The advent of massively parallel supercomputers has enhanced the scientific community's ....... The GPAW code was ported an optimized for the Blue Gene/P architecture. We present our algorithmic parallelization strategy and interpret the results for a number of benchmark test cases.......'s ability to study larger system sizes. Ground-state DFT calculations on∼103 valence electrons using traditional O(N3) algorithms can be routinely performed on present-day supercomputers. The performance characteristics of these massively parallel DFT codes on>104 computer cores are not well understood...
Directory of Open Access Journals (Sweden)
A A Shokri
2013-10-01
Full Text Available In this paper, we have investigated the spin-dependent transport properties and electron entanglement in a mesoscopic system, which consists of two semi-infinite leads (as source and drain separated by a typical quantum wire with a given potential. The properties studied include current-voltage characteristic, electrical conductivity, Fano factor and shot noise, and concurrence. The calculations are based on the transfer matrix method within the effective mass approximation. Using the Landauer formalism and transmission coefficient, the dependence of the considered quantities on type of potential well, length and width of potential well, energy of transmitted electron, temperature and the voltage have been theoretically studied. Also, the effect of the above-mentioned factors has been investigated in the nanostructure. The application of the present results may be useful in designing spintronice devices.
Directory of Open Access Journals (Sweden)
B.Andriyevsky
2007-01-01
Full Text Available First principle calculations of the effect of hydrostatic pressure on the structural and electronic parameters of TGS crystals have been carried out within the framework of density functional theory using the CASTEP code. The volume dependence of total electronic energy E(V of the crystal unit cell satisfies the third-order Birch-Murnaghan isothermal equation of state. For the pressure range of -5...5 GPa, the bulk modulus was found to be equal to K=45 ± 5 GPa. The relative pressure changes of the unit cell parameters were found to be linear in the range of -5...5 GPa. Crossing of the pressure dependencies of enthalpy corresponding to the ferroelectric and non-ferroelectric phases at P=7.7 GPa testifies to the probable pressure induced phase transition in TGS crystal.
Fernandez, Michael; Bilić, Ante; Barnard, Amanda S.
2017-09-01
Computational screening is key to understanding structure-function relationships at the nanoscale but the high computational cost of accurate electronic structure calculations remains a bottleneck for the screening of large nanomaterial libraries. In this work we propose a data-driven strategy to predict accuracy differences between different levels of theory. Machine learning (ML) models are trained with structural features of graphene nanoflakes to predict the differences between electronic properties at two levels of approximation. The ML models yield an overall accuracy of 94% and 88%, for energy of the Fermi level and the band gap, respectively. This strategy represents a successful application of established ML methods to the selection of optimum level of theory, enabling more rapid and efficient screening of nanomaterials, and is extensible to other materials and computational methods.
Yang, Hua
2012-01-01
Electronic structure and optical properties of α-FeMO 3 systems (M = Sc, Ti, V, Cr, Cu, Cd or In) have been investigated using first principles calculations. All of the FeMO 3 systems have a large net magnetic moment. The ground state of pure α-Fe 2O 3 is an antiferromagnetic insulator. For M = Cu or Cd, the systems are half-metallic. Strong absorption in the visible region can be observed in the Cu and Cd-doped systems. Systems with M = Sc, Ti, V, Cr or In are not half-metallic and are insulators. The strongest peaks shift toward shorter wavelengths in the absorption spectra. It is concluded that transition metal doping can modify the electronic structure and optical properties of α-FeMO 3 systems. This journal is © 2012 The Royal Society of Chemistry.
Significance of Accurate Electronic Structure Calculation Methods in Designing Silicon Donor Qubits
Mohiyaddin, Fahd; Jakowski, Jacek; Huang, Jingsong; Ericson, Milton Nance; Britton, Charles; Curtis, Franklin; Dumitrescu, Eugene; Sumpter, Bobby; Humble, Travis
Recent demonstrations of long-lived spin qubits with high control fidelity have enhanced the potential of silicon donors in quantum computing. Verifying the design of prototype silicon qubit devices using computational models provides insight into their electrostatic potential landscape, donor electron wave functions, and spin dynamics. Here, we examine the sensitivity of device verification to the underlying electronic structure model used for the donor. Within the context of a computational workflow, we observe a significant discrepancy in the amplitude of the donor wave function computed using density-functional theory versus tight-binding methods for the case of doped silicon nanocrystals. While both methods can be used to match experimental values for the hyperfine coupling, differences in the calculated electronic amplitude at the donor site suggest that more complicated interactions, e.g., electron-exchange, may become unreliable. Hence, an accurate understanding of the donor wave function in the donor vicinity is critical to device design, as it serves as a handle to vital parameters in donor based quantum computer architectures.
Gidofalvi, Gergely
2014-01-01
Molecule-optimized basis sets, based on approximate natural orbitals, are developed for accelerating the convergence of quantum calculations with strongly correlated (multi-referenced) electrons. We use a low-cost approximate solution of the anti-Hermitian contracted Schr{\\"o}dinger equation (ACSE) for the one- and two-electron reduced density matrices (RDMs) to generate an approximate set of natural orbitals for strongly correlated quantum systems. The natural-orbital basis set is truncated to generate a molecule-optimized basis set whose rank matches that of a standard correlation-consistent basis set optimized for the atoms. We show that basis-set truncation by approximate natural orbitals can be viewed as a one-electron unitary transformation of the Hamiltonian operator and suggest an extension of approximate natural-orbital truncations through two-electron unitary transformations of the Hamiltonian operator, such as those employed in the solution of the ACSE. The molecule-optimized basis set from the ACS...
Improved calculation on the isotope effect in dissociative electron attachment to acetylene
Chourou, S. T.; Orel, A. E.
2009-09-01
We performed nuclear dynamics calculations on C2H2 and C2D2 to study the isotope effect in dissociative electron attachment (DEA). Our previous calculations at 0 K led to a ratio σ0→DEA(C2H-)/σ0→DEA(C2D-) of about 28.9 which is about a factor of 2 higher than recent experimental results. This discrepancy was attributed to the contribution of higher vibrational modes in the yield of the anion fragments. We included the four lowest bending vibrational states presenting nonvanishing populations at the experiment temperature of T=333K . The resulting ratio is found to be 17.9 which is in closer agreement with the measured value.
Photon and electron absorbed fractions calculated from a new tomographic rat model
Energy Technology Data Exchange (ETDEWEB)
Peixoto, P H R [Departamento de Energia Nuclear, Universidade Federal de Pernambuco, Av. Prof. Luiz Freire 1000, Cidade Universitaria, CEP 50740-540, Recife, PE (Brazil); Vieira, J W [Centro Federal de Educacao Tecnologica de Pernambuco, Recife, PE (Brazil); Yoriyaz, H [Instituto de Pesquisas Energeticas e Nucleares, Sao Paulo, SP (Brazil); Lima, F R A [Centro Regional de Ciencias Nucleares-CNEN, Recife, PE (Brazil)], E-mail: phrpeixoto@yahoo.com.br
2008-10-07
This paper describes the development of a tomographic model of a rat developed using CT images of an adult male Wistar rat for radiation transport studies. It also presents calculations of absorbed fractions (AFs) under internal photon and electron sources using this rat model and the Monte Carlo code MCNP. All data related to the developed phantom were made available for the scientific community as well as the MCNP inputs prepared for AF calculations in that phantom and also all estimated AF values, which could be used to obtain absorbed dose estimates-following the MIRD methodology-in rats similar in size to the presently developed model. Comparison between the rat model developed in this study and that published by Stabin et al (2006 J. Nucl. Med. 47 655) for a 248 g Sprague-Dawley rat, as well as between the estimated AF values for both models, has been presented.
Equation-of-motion coupled cluster method for high spin double electron attachment calculations
Energy Technology Data Exchange (ETDEWEB)
Musiał, Monika, E-mail: musial@ich.us.edu.pl; Lupa, Łukasz; Kucharski, Stanisław A. [Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice (Poland)
2014-03-21
The new formulation of the equation-of-motion (EOM) coupled cluster (CC) approach applicable to the calculations of the double electron attachment (DEA) states for the high spin components is proposed. The new EOM equations are derived for the high spin triplet and quintet states. In both cases the new equations are easier to solve but the substantial simplification is observed in the case of quintets. Out of 21 diagrammatic terms contributing to the standard DEA-EOM-CCSDT equations for the R{sub 2} and R{sub 3} amplitudes only four terms survive contributing to the R{sub 3} part. The implemented method has been applied to the calculations of the excited states (singlets, triplets, and quintets) energies of the carbon and silicon atoms and potential energy curves for selected states of the Na{sub 2} (triplets) and B{sub 2} (quintets) molecules.
Brandelik, Andreas
2009-07-01
CALCMIN, an open source Visual Basic program, was implemented in EXCEL™. The program was primarily developed to support geoscientists in their routine task of calculating structural formulae of minerals on the basis of chemical analysis mainly obtained by electron microprobe (EMP) techniques. Calculation programs for various minerals are already included in the form of sub-routines. These routines are arranged in separate modules containing a minimum of code. The architecture of CALCMIN allows the user to easily develop new calculation routines or modify existing routines with little knowledge of programming techniques. By means of a simple mouse-click, the program automatically generates a rudimentary framework of code using the object model of the Visual Basic Editor (VBE). Within this framework simple commands and functions, which are provided by the program, can be used, for example, to perform various normalization procedures or to output the results of the computations. For the clarity of the code, element symbols are used as variables initialized by the program automatically. CALCMIN does not set any boundaries in complexity of the code used, resulting in a wide range of possible applications. Thus, matrix and optimization methods can be included, for instance, to determine end member contents for subsequent thermodynamic calculations. Diverse input procedures are provided, such as the automated read-in of output files created by the EMP. Furthermore, a subsequent filter routine enables the user to extract specific analyses in order to use them for a corresponding calculation routine. An event-driven, interactive operating mode was selected for easy application of the program. CALCMIN leads the user from the beginning to the end of the calculation process.
Srivastava, Vipul; Aynyas, M.; Rajagopalan, M.; Sanyal, S. P.
2008-04-01
Electronic properties of non-magnetic cubic B2-type AIRE (RE = La, Ce and Pr) compounds have been derived from self-consistent tight binding linear muffin tin orbital method at ambient pressure. These compounds show metallic behaviour under ambient conditions. While thermal properties like Debye temperature and Grüneisen constant are calculated at T = 0 K within the Debye-Grüneisen model and compared with the others theoretical results. We have also performed a pressure induced variation of Debye temperature. We have found a decrease in Debye temperature around 40 kbar in all the AIRE compounds.
The electronic structure of TiCl: ligand field versus density functional calculations
Focsa, C.; Bencheikh, M.; Pettersson, L. G. M.
1998-07-01
The electronic structures of titanium chloride and its cation have been analysed by means of both ligand field (LFT) and density functional (DFT) theories. Despite the discrepancy between the DFT and LFT concerning the assignment of the ground state of 0953-4075/31/13/006/img6, an overall agreement is seen for TiCl. The observed 0953-4075/31/13/006/img7 ground state is found to result from our calculated 0953-4075/31/13/006/img8 ground state by a 0953-4075/31/13/006/img9 ionization process with an energy of 0953-4075/31/13/006/img10.
Energy Technology Data Exchange (ETDEWEB)
Dougar-Jabon, V.D. [Escuela de Fisica, Universidad Industrial de Santander, A.A. 678, Bucaramanga (Colombia); Umnov, A.M. [Russian Friendship University, 117198 Moscow (Russia); Kutner, V.B. [Joint Institute for Nuclear Research, Dubna (Russia)
1996-03-01
It is common knowledge that the electrostatic pit in a core plasma of electron cyclotron resonance sources exerts strict control over generation of ions in high charge states. This work is aimed at finding a dependence of the lifetime of ions on their charge states in the core region and to elaborate a numerical model of ion charge dispersion not only for the core plasmas but for extracted beams as well. The calculated data are in good agreement with the experimental results on charge distributions and magnitudes for currents of beams extracted from the 14 GHz DECRIS source. {copyright} {ital 1996 American Institute of Physics.}
Domain overlap matrices from plane-wave-based methods of electronic structure calculation
Golub, Pavlo; Baranov, Alexey I.
2016-10-01
Plane waves are one of the most popular and efficient basis sets for electronic structure calculations of solids; however, their delocalized nature makes it difficult to employ for them classical orbital-based methods of chemical bonding analysis. The quantum chemical topology approach, introducing chemical concepts via partitioning of real space into chemically meaningful domains, has no difficulties with plane-wave-based basis sets. Many popular tools employed within this approach, for instance delocalization indices, need overlap integrals over these domains—the elements of the so called domain overlap matrices. This article reports an efficient algorithm for evaluation of domain overlap matrix elements for plane-wave-based calculations as well as evaluation of its implementation for one of the most popular projector augmented wave (PAW) methods on the small set of simple and complex solids. The stability of the obtained results with respect to PAW calculation parameters has been investigated, and the comparison of the results with the results from other calculation methods has also been made.
First principles electron-correlated calculations of optical absorption in magnesium clusters★
Shinde, Ravindra; Shukla, Alok
2017-11-01
In this paper, we report large-scale configuration interaction (CI) calculations of linear optical absorption spectra of various isomers of magnesium clusters Mgn (n = 2-5), corresponding to valence transitions. Geometry optimization of several low-lying isomers of each cluster was carried out using coupled-cluster singles doubles (CCSD) approach, and these geometries were subsequently employed to perform ground and excited state calculations using either the full-CI (FCI) or the multi-reference singles-doubles configuration interaction (MRSDCI) approach, within the frozen-core approximation. Our calculated photoabsorption spectrum of magnesium dimer (Mg2) is in excellent agreement with the experiments both for peak positions, and intensities. Owing to the sufficiently inclusive electron-correlation effects, these results can serve as benchmarks against which future experiments, as well as calculations performed using other theoretical approaches, can be tested. Supplementary material in the form of one pdf fille available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-80356-6.
Transport coefficients for electrons in water vapor: definition, measurement, and calculation.
Robson, R E; White, R D; Ness, K F
2011-02-14
Comparison of experimental and theoretical transport data for electron swarms in water vapour over a wide range of fields provides a rigorous test of (e(-), H(2)O) scattering cross sections over a correspondingly broad range of energies. That like should be compared with like is axiomatic, but the definition of transport coefficients at high fields, when non-conservative processes are significant, has long been contentious. This paper revisits and distills the most essential aspects of the definition and calculation of transport coefficients, giving numerical results for the drift velocity and ionisation coefficient of electrons in water vapour. In particular, the relationship between the theoretically calculated bulk drift velocities of [K. F. Ness and R. E. Robson, Phys. Rev. A 38, 1446 (1988)] and the experimental "arrival time spectra" drift velocity data of Hasegawa et al. [J. Phys. D 40(8), 2495 (2007)] is established. This enables the Hasegawa et al. data to be reconciliated with the previous literature, and facilitates selection of the best (e(-), H(2)O) cross section set.
Comparisons of Calculations with PARTRAC and NOREC: Transport of Electrons in Liquid Water
Dingfelder, M.; Ritchie, R. H.; Turner, J. E.; Friedland, W.; Paretzke, H. G.; Hamm, R. N.
2013-01-01
Monte Carlo computer models that simulate the detailed, event-by-event transport of electrons in liquid water are valuable for the interpretation and understanding of findings in radiation chemistry and radiation biology. Because of the paucity of experimental data, such efforts must rely on theoretical principles and considerable judgment in their development. Experimental verification of numerical input is possible to only a limited extent. Indirect support for model validity can be gained from a comparison of details between two independently developed computer codes as well as the observable results calculated with them. In this study, we compare the transport properties of electrons in liquid water using two such models, PARTRAC and NOREC. Both use interaction cross sections based on plane-wave Born approximations and a numerical parameterization of the complex dielectric response function for the liquid. The models are described and compared, and their similarities and differences are highlighted. Recent developments in the field are discussed and taken into account. The calculated stopping powers, W values, and slab penetration characteristics are in good agreement with one another and with other independent sources. PMID:18439039
Hou, Ling; Li, Wei-Dong; Wang, Fangwei; Eriksson, Olle; Wang, Bao-Tian
2017-12-01
We present a systematic investigation of the structural, magnetic, electronic, mechanical, and thermodynamic properties of CmO2 with the local density approximation (LDA)+U and the generalized gradient approximation (GGA)+U approaches. The strong Coulomb repulsion and the spin-orbit coupling (SOC) effects on the lattice structures, electronic density of states, and band gaps are carefully studied, and compared with other A O2 (A =U , Np, Pu, and Am). The ferromagnetic configuration with half-metallic character is predicted to be energetically stable while a charge-transfer semiconductor is predicted for the antiferromagnetic configuration. The elastic constants and phonon spectra show that the fluorite structure is mechanically and dynamically stable. Based on the first-principles phonon density of states, the lattice vibrational energy is calculated using the quasiharmonic approximation. Then, the Gibbs free energy, thermal expansion coefficient, specific heat, and entropy are obtained and compared with experimental data. The mode Grüneisen parameters are presented to analyze the anharmonic properties. The Slack relation is applied to obtain the lattice thermal conductivity in temperature range of 300-1600 K. The phonon group velocities are also calculated to investigate the heat transfer. For all these properties, if available, we compare the results of CmO2 with other A O2 .
Considerations of beta and electron transport in internal dose calculations. Progress report
Energy Technology Data Exchange (ETDEWEB)
Bolch, W.E.
1994-11-01
The goal of this particular task is to consider, for the first time, the explicit transport of beta particles and photon-generated electrons in the series of six phantoms developed by Cristy and Eckerman (1987) at the Oak Ridge National Laboratory. In their report, ORNL/TM-8381, specific absorbed fractions of energy are reported for phantoms representing the newborn (3.4 kg), the one-year-old (9.8 kg), the five-year-old (19 kg), the ten-year-old (32 kg), the fifteen-year-old/adult female (55-58 kg), and the adult male (70 kg). Radiation transport calculations were performed with the Monte Carlo code ALGAMP which allows photon transport only. In subsequent calculations of radionuclide S values as is done in the MIRDOSE2 computer program, electron absorbed fractions are thus considered to be either unity or zero depending upon whether the source region does or does not equal the target region, respectively.
Time domain numerical calculations of the short electron bunch wakefields in resistive structures
Energy Technology Data Exchange (ETDEWEB)
Tsakanian, Andranik
2010-10-15
The acceleration of electron bunches with very small longitudinal and transverse phase space volume is one of the most actual challenges for the future International Linear Collider and high brightness X-Ray Free Electron Lasers. The exact knowledge on the wake fields generated by the ultra-short electron bunches during its interaction with surrounding structures is a very important issue to prevent the beam quality degradation and to optimize the facility performance. The high accuracy time domain numerical calculations play the decisive role in correct evaluation of the wake fields in advanced accelerators. The thesis is devoted to the development of a new longitudinally dispersion-free 3D hybrid numerical scheme in time domain for wake field calculation of ultra short bunches in structures with walls of finite conductivity. The basic approaches used in the thesis to solve the problem are the following. For materials with high but finite conductivity the model of the plane wave reflection from a conducting half-space is used. It is shown that in the conductive half-space the field components perpendicular to the interface can be neglected. The electric tangential component on the surface contributes to the tangential magnetic field in the lossless area just before the boundary layer. For high conducting media, the task is reduced to 1D electromagnetic problem in metal and the so-called 1D conducting line model can be applied instead of a full 3D space description. Further, a TE/TM (''transverse electric - transverse magnetic'') splitting implicit numerical scheme along with 1D conducting line model is applied to develop a new longitudinally dispersion-free hybrid numerical scheme in the time domain. The stability of the new hybrid numerical scheme in vacuum, conductor and bound cell is studied. The convergence of the new scheme is analyzed by comparison with the well-known analytical solutions. The wakefield calculations for a number of
Haider, S. A.; Kim, J.; Nagy, A. F.; Keller, C. N.; Verigin, M. I.; Gringauz, K. I.; Shutte, N. M.; Szego, K.; Kiraly, P.
1992-01-01
The calculations presented in this paper clearly establish that the electron fluxes measured by the HARP instrument, carried on board Phobos 2, could cause significant electron impact ionization and excitation in the nightside atmosphere of Mars, if these electrons actually do precipitate. The calculated peak electron densities were found to be about a factor of 2 larger than the mean observed nightside densities, indicating that if a significant fraction of the measured electrons actually precipitate, they could be the dominant mechanism responsible for maintaining the nightside ionosphere. The calculated zenith column emission rates of the O I 5577-A and 6300-A and CO Cameron band emissions, due to electron impact and dissociative recombination mechanisms, were found to be significant.
Zhu, Jinhan; Chen, Lixin; Chen, Along; Luo, Guangwen; Deng, Xiaowu; Liu, Xiaowei
2015-01-01
Purpose To use a graphic processing unit (GPU) calculation engine to implement a fast 3D pre-treatment dosimetric verification procedure based on an electronic portal imaging device (EPID). Methods The GPU algorithm includes the deconvolution and convolution method for the fluence-map calculations, the collapsed-cone convolution/superposition (CCCS) algorithm for the 3D dose calculations and the 3D gamma evaluation calculations. The results of the GPU-based CCCS algorithm were compared to tho...
Stanke, Monika; Jurkowski, Jacek; Adamowicz, Ludwik
2017-03-01
Algorithms for calculating the quantum electrodynamics Araki-Sucher correction for n-electron explicitly correlated molecular Gaussian functions with shifted centers are derived and implemented. The algorithms are tested in calculations concerning the H2 molecule and applied in ground-state calculations of LiH and {{{H}}}3+ molecules. The implementation will significantly increase the accuracy of the calculations of potential energy surfaces of small diatomic and triatomic molecules and their rovibrational spectra.
Mechanical, Electronic, and Optical Properties of β-B6O: First-Principles Calculations
Yang, Ruike; Ma, Shaowei; Wei, Qun; Du, Zheng
2017-08-01
The mechanical, electronic, and optical properties of β-B6O are calculated by first-principles. The structural optimization and all properties are calculated by the method of generalized gradient approximation - Perdew, Burke and Ernzerhof (PBE). The hardness of β-B6O is 39 GPa under a pressure of 0 GPa, which indicates that it belongs to a hard material. The band gap is indirect with a value of 1.836 eV, showing that β-B6O is a semiconductor. The research of the electron localization function shows that the bonds of β-B6O are covalent bonds, which can increase the stability of the compound. The phonon dispersion curves present the dynamical stability of β-B6O under pressures of 0 and 50 GPa. The optical properties of β-B6O are also calculated. In the energy range from 0 to 18 eV, β-B6O presents high reflectivity; it has a strong absorption in the energy range from 3 to 18 eV. The refractive index results show that light propagates through the β-B6O in a difficult manner in the energy range from 6.9 to 16.5 eV. In addition, the energy of the plasma frequency for β-B6O is 16.6 eV and the peak value of the loss function is 13.6. These properties provide the basis for the development and application of β-B6O.
Stanke, Monika; Palikot, Ewa; Adamowicz, Ludwik
2016-05-01
Algorithms for calculating the leading mass-velocity (MV) and Darwin (D) relativistic corrections are derived for electronic wave functions expanded in terms of n-electron explicitly correlated Gaussian functions with shifted centers and without pre-exponential angular factors. The algorithms are implemented and tested in calculations of MV and D corrections for several points on the ground-state potential energy curves of the H2 and LiH molecules. The algorithms are general and can be applied in calculations of systems with an arbitrary number of electrons.
Energy Technology Data Exchange (ETDEWEB)
Stanke, Monika, E-mail: monika@fizyka.umk.pl; Palikot, Ewa, E-mail: epalikot@doktorant.umk.pl [Institute of Physics, Faculty of Physics, Astronomy, and Informatics, Nicolaus Copernicus University, ul. Grudzia̧dzka 5, Toruń, PL 87-100 (Poland); Adamowicz, Ludwik, E-mail: ludwik@email.arizona.edu [Department of Chemistry and Biochemistry and Department of Physics, University of Arizona, Tucson, Arizona 85721 (United States)
2016-05-07
Algorithms for calculating the leading mass-velocity (MV) and Darwin (D) relativistic corrections are derived for electronic wave functions expanded in terms of n-electron explicitly correlated Gaussian functions with shifted centers and without pre-exponential angular factors. The algorithms are implemented and tested in calculations of MV and D corrections for several points on the ground-state potential energy curves of the H{sub 2} and LiH molecules. The algorithms are general and can be applied in calculations of systems with an arbitrary number of electrons.
Potential energy curves of Li+2 from all-electron EA-EOM-CCSD calculations
Musiał, Monika; Medrek, Magdalena; Kucharski, Stanisław A.
2015-10-01
The electron attachment (EA) equation-of-motion coupled-cluster theory provides description of the states obtained by the attachment of an electron to the reference system. If the reference is assumed to be a doubly ionised cation, then the EA results relate to the singly ionised ion. In the current work, the above scheme is applied to the calculations of the potential energy curves (PECs) of the Li+2 cation adopting the doubly ionised Li2 +2 structure as the reference system. The advantage of such computational strategy relies on the fact that the closed-shell Li2 +2 reference dissociates into closed-shell fragments (Li2 +2 ⇒ Li+ + Li+), hence the RHF (restricted Hartree-Fock) function can be used as the reference in the whole range of interatomic distances. This scheme offers the first principle method without any model or effective potential parameters for the description of the bond-breaking processes. In this study, the PECs and selected spectroscopic constants for 18 electronic states of the Li+2 ion were computed and compared with experimental and other theoretical results. †In honour of Professor Sourav Pal on the occasion of an anniversary in his private and scientific life.
Improved calculations of electron capture transitions for decay data and radionuclide metrology.
Mougeot, X
2017-07-15
Electron capture properties are crucial to establish the decay schemes of numerous radionuclides. The present modelling aims at improving the theoretical estimates of these decays, which are needed when no measurement is available. Allowed and forbidden unique transitions are calculated on the basis of precise relativistic wave functions of the atomic electrons, determined in previous work. In this context, correcting for atomic effects is of high importance. The two common approaches from Bahcall and Vatai to correct for the overlap and exchange effects have been extended to every subshell in a unified formulation, with the electron occupation precisely taken into account. The shake-up and shake-off effects, which create secondary vacancies, and the influence of the hole due to the capture process, have been considered. Uncertainties are also estimated. Relative capture probabilities and their ratios, including capture-to-positron ratios, have been found to be in good agreement with a selection of precise measurements. This modelling was then applied to the third forbidden unique transition of 40K decay, with an update of the recommended values for the branching ratios and the total decay half-life. Copyright © 2017 Elsevier Ltd. All rights reserved.
Nakano, Hiroshi; Yamamoto, Takeshi
2012-04-07
Quantum mechanical/molecular mechanical (QM/MM) free energy calculation presents a significant challenge due to an excessive number of QM calculations. A useful approach for reducing the computational cost is that based on the mean field approximation to the QM subsystem. Here, we describe such a mean-field QM/MM theory for electronically polarizable systems by starting from the Hartree product ansatz for the total system and invoking a variational principle of free energy. The MM part is then recast to a classical polarizable model by introducing the charge response kernel. Numerical test shows that the potential of mean force (PMF) thus obtained agrees quantitatively with that obtained from a direct QM/MM calculation, indicating the utility of self-consistent mean-field approximation. Next, we apply the obtained method to prototypical reactions in several qualitatively different solvents and make a systematic comparison of polarization effects. The results show that in aqueous solution the PMF does not depend very much on the water models employed, while in nonaqueous solutions the PMF is significantly affected by explicit polarization. For example, the free energy barrier for a phosphoryl dissociation reaction in acetone and cyclohexane is found to increase by more than 10 kcal/mol when switching the solvent model from an empirical to explicitly polarizable one. The reason for this is discussed based on the parametrization of empirical nonpolarizable models.
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Lin, Lin; Chen, Mohan; Yang, Chao; He, Lixin
2012-02-10
We describe how to apply the recently developed pole expansion plus selected inversion (PEpSI) technique to Kohn-Sham density function theory (DFT) electronic structure calculations that are based on atomic orbital discretization. We give analytic expressions for evaluating charge density, total energy, Helmholtz free energy and atomic forces without using the eigenvalues and eigenvectors of the Kohn-Sham Hamiltonian. We also show how to update the chemical potential without using Kohn-Sham eigenvalues. The advantage of using PEpSI is that it has a much lower computational complexity than that associated with the matrix diagonalization procedure. We demonstrate the performance gain by comparing the timing of PEpSI with that of diagonalization on insulating and metallic nanotubes. For these quasi-1D systems, the complexity of PEpSI is linear with respect to the number of atoms. This linear scaling can be observed in our computational experiments when the number of atoms in a nanotube is larger than a few hundreds. Both the wall clock time and the memory requirement of PEpSI is modest. This makes it even possible to perform Kohn-Sham DFT calculations for 10,000-atom nanotubes on a single processor. We also show that the use of PEpSI does not lead to loss of accuracy required in a practical DFT calculation.
Seiler, Christian
2016-01-01
A formalism for electronic-structure calculations is presented that is based on the functional renormalization group (FRG). The traditional FRG has been formulated for systems that exhibit a translational symmetry with an associated Fermi surface, which can provide the organization principle for the renormalization group (RG) procedure. We here advance an alternative formulation, where the RG-flow is organized in the energy-domain rather than in k-space. This has the advantage that it can also be applied to inhomogeneous matter lacking a band-structure, such as disordered metals or molecules. The energy-domain FRG ({\\epsilon}FRG) presented here accounts for Fermi-liquid corrections to quasi-particle energies and particle-hole excitations. It goes beyond the state of the art GW-BSE, because in {\\epsilon}FRG the Bethe-Salpeter equation (BSE) is solved in a self-consistent manner. An efficient implementation of the approach that has been tested against exact diagonalization calculations and calculations based on...
First-principles calculations of the electronic and structural properties of GaSb
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Castaño-González, E.-E. [Universidad del Norte, Grupo de Investigación en Física Aplicada, Departamento de Física (Colombia); Seña, N. [Universidad Nacional de Colombia-Colombia, Departamento de Física, Grupo de Materiales Nanoestructurados y sus Aplicaciones (Colombia); Mendoza-Estrada, V.; González-Hernández, R., E-mail: rhernandezj@uninorte.edu.co [Universidad del Norte, Grupo de Investigación en Física Aplicada, Departamento de Física (Colombia); Dussan, A. [Universidad Nacional de Colombia-Colombia, Departamento de Física, Grupo de Materiales Nanoestructurados y sus Aplicaciones (Colombia); Mesa, F., E-mail: fredy.mesa@urosario.edu.co [Universidad del Rosario, Grupo NanoTech, Facultad de Ciencias Naturales y Matemáticas (Colombia)
2016-10-15
In this paper, we carried out first-principles calculations in order to investigate the structural and electronic properties of the binary compound gallium antimonide (GaSb). This theoretical study was carried out using the Density Functional Theory within the plane-wave pseudopotential method. The effects of exchange and correlation (XC) were treated using the functional Local Density Approximation (LDA), generalized gradient approximation (GGA): Perdew–Burke–Ernzerhof (PBE), Perdew-Burke-Ernzerhof revised for solids (PBEsol), Perdew-Wang91 (PW91), revised Perdew–Burke–Ernzerhof (rPBE), Armiento–Mattson 2005 (AM05) and meta-generalized gradient approximation (meta-GGA): Tao–Perdew–Staroverov–Scuseria (TPSS) and revised Tao–Perdew–Staroverov–Scuseria (RTPSS) and modified Becke-Johnson (MBJ). We calculated the densities of state (DOS) and band structure with different XC potentials identified and compared them with the theoretical and experimental results reported in the literature. It was discovered that functional: LDA, PBEsol, AM05 and RTPSS provide the best results to calculate the lattice parameters (a) and bulk modulus (B{sub 0}); while for the cohesive energy (E{sub coh}), functional: AM05, RTPSS and PW91 are closer to the values obtained experimentally. The MBJ, Rtpss and AM05 values found for the band gap energy is slightly underestimated with those values reported experimentally.
Evaluation of electronic states of implanted materials by molecular orbital calculation
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Saito, Jun-ichi; Kano, Shigeki [Power Reactor and Nuclear Fuel Development Corp., Oarai, Ibaraki (Japan). Oarai Engineering Center
1997-07-01
In order to understand the effect of implanted atom in ceramics and metals on the sodium corrosion, the electronic structures of un-implanted and implanted materials were calculated using DV-X{alpha} cluster method which was one of molecular orbital calculations. The calculated materials were {beta}-Si{sub 3}N{sub 4}, {alpha}-SiC and {beta}-SiC as ceramics, and f.c.c. Fe, b.c.c. Fe and b.c.c. Nb as metals. An Fe, Mo and Hf atom for ceramics, and N atom for metals were selected as implanted atoms. Consequently, it is expected that the corrosion resistance of {beta}-Si{sub 3}N{sub 4} is improved, because the ionic bonding reduced by the implantation. When the implanted atom is occupied at interstitial site in {alpha}-SiC and {beta}-SiC, the ionic bonding reduced. Hence, there is a possibility to improve the corrosion resistance of {alpha}-SiC and {beta}-SiC. It is clear that Hf is most effective element among implanted atoms in this study. As the covalent bond between N atom and surrounding Fe atoms increased largely in f.c.c. Fe by N implantation, it was expected that the corrosion resistance of f.c.c. Fe improved in liquid sodium. (J.P.N.)
Li, Rui; Cao, Hong; Dong, Jinming
2017-11-01
The electronic properties of one-dimensional (1D) group-IV monochalcogenide ribbons, denoted as MXNRs (Mdbnd Ge, Sn; Xdbnd S, Se), are investigated by the density functional theory calculations. It is found from our calculations that all the MXNRs with zigzag edges are metals, because there are two edge bands crossing the Fermi level, which come from the py and pz orbital of edge M atoms and py ones of edge X atoms. In contrast, all the MXNRs with armchair edges (arm-MXNRs) are semiconductors, independent of the ribbon widths. Their band gaps are found to fluctuate, which vary with the ribbon width, finally converging to the values of the corresponding 2D MX compounds. It is important to find that except for the arm-SnSNRs, other three narrow arm-MXNRs exhibit repeatedly band gap transitions between the direct and indirect ones as their widths increase because of the edge symmetry and quantum confinement effect of the 1D ribbons. The calculated binding energies indicate that the arm-MXNRs are generally more stable than the zig-MXNRs. In addition, the hydrogen-terminated GeSNRs are also studied, which exhibit semiconducting properties no matter their edges are zigzag or armchair.
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Goldsmith, Zachary K.; Harshan, Aparna K.; Gerken, James B.; Vörös, Márton; Galli, Giulia; Stahl, Shannon S.; Hammes-Schiffer, Sharon
2017-03-06
NiFe oxyhydroxide materials are highly active electrocatalysts for the oxygen evolution reaction (OER), an important process for carbon-neutral energy storage. Recent spectroscopic and computational studies increasingly support iron as the site of catalytic activity but differ with respect to the relevant iron redox state. A combination of hybrid periodic density functional theory calculations and spectroelectrochemical experiments elucidate the electronic structure and redox thermodynamics of Ni-only and mixed NiFe oxyhydroxide thin-film electrocatalysts. The UV/visible light absorbance of the Ni-only catalyst depends on the applied potential as metal ions in the film are oxidized before the onset of OER activity. In contrast, absorbance changes are negligible in a 25% Fe-doped catalyst up to the onset of OER activity. First-principles calculations of proton-coupled redox potentials and magnetizations reveal that the Ni-only system features oxidation of Ni2+ to Ni3+, followed by oxidation to a mixed Ni3+/4+ state at a potential coincident with the onset of OER activity. Calculations on the 25% Fedoped system show the catalyst is redox inert before the onset of catalysis, which coincides with the formation of Fe4+ and mixed Ni oxidation states. The calculations indicate that introduction of Fe dopants changes the character of the conduction band minimum from Ni-oxide in the Ni-only to predominantly Fe-oxide in the NiFe electrocatalyst. These findings provide a unified experimental and theoretical description of the electrochemical and optical properties of Ni and NiFe oxyhydroxide electrocatalysts and serve as an important benchmark for computational characterization of mixedmetal oxidation states in heterogeneous catalysts.
Energy Technology Data Exchange (ETDEWEB)
Wang, Lin-Wang
2006-12-01
Quantum mechanical ab initio calculation constitutes the biggest portion of the computer time in material science and chemical science simulations. As a computer center like NERSC, to better serve these communities, it will be very useful to have a prediction for the future trends of ab initio calculations in these areas. Such prediction can help us to decide what future computer architecture can be most useful for these communities, and what should be emphasized on in future supercomputer procurement. As the size of the computer and the size of the simulated physical systems increase, there is a renewed interest in using the real space grid method in electronic structure calculations. This is fueled by two factors. First, it is generally assumed that the real space grid method is more suitable for parallel computation for its limited communication requirement, compared with spectrum method where a global FFT is required. Second, as the size N of the calculated system increases together with the computer power, O(N) scaling approaches become more favorable than the traditional direct O(N{sup 3}) scaling methods. These O(N) methods are usually based on localized orbital in real space, which can be described more naturally by the real space basis. In this report, the author compares the real space methods versus the traditional plane wave (PW) spectrum methods, for their technical pros and cons, and the possible of future trends. For the real space method, the author focuses on the regular grid finite different (FD) method and the finite element (FE) method. These are the methods used mostly in material science simulation. As for chemical science, the predominant methods are still Gaussian basis method, and sometime the atomic orbital basis method. These two basis sets are localized in real space, and there is no indication that their roles in quantum chemical simulation will change anytime soon. The author focuses on the density functional theory (DFT), which is the
Nancy Anna Anasthasiya, A.; Khaneja, Mamta; Jeyaprakash, B. G.
2017-10-01
Ammonia adsorption on graphene (G) and graphene oxide (GO) was investigated through density functional theory calculations. In the GO system, the obtained binding energy, band gap, charge transfer and electronic structure revealed that the epoxide (GO-O) and hydroxyl groups (GO-OH) in GO enhance the NH3 adsorption, which leads to the chemisorption of NH3 on GO. The dissociation of NH3 to NH2 and formation of OH was also observed when the O and H atoms were separated at 0.985 Å, 1.019 Å, 1.035 Å, and 1.044 Å for various GO systems. The maximum charge transfer value was found to be 0.054 |e| with the binding energy of 1.143 eV for GO with a single epoxide (GO-1O) group. The charge transfer from NH3 to G or GO and the bond formation in this study agree with the reported experimental results.
Seibert, Jakob; Bannwarth, Christoph; Grimme, Stefan
2017-08-30
A fully quantum mechanical (QM) treatment to calculate electronic absorption (UV-vis) and circular dichroism (CD) spectra of typical biomolecules with thousands of atoms is presented. With our highly efficient sTDA-xTB method, spectra averaged along structures from molecular dynamics (MD) simulations can be computed in a reasonable time frame on standard desktop computers. This way, nonequilibrium structure and conformational, as well as purely quantum mechanical effects like charge-transfer or exciton-coupling, are included. Different from other contemporary approaches, the entire system is treated quantum mechanically and neither fragmentation nor system-specific adjustment is necessary. Among the systems considered are a large DNA fragment, oligopeptides, and even entire proteins in an implicit solvent. We propose the method in tandem with experimental spectroscopy or X-ray studies for the elucidation of complex (bio)molecular structures including metallo-proteins like myoglobin.
DWBA-G calculations of electron impact ionization of noble gas atoms
Energy Technology Data Exchange (ETDEWEB)
Kheifets, A S [Research School of Physical Sciences and Engineering, The Australian National University, Canberra ACT 0200 (Australia); Naja, A; Casagrande, E M Staicu; Lahmam-Bennani, A [Universite Paris-Sud 11, Laboratoire des Collisions Atomiques et Moleculaires (LCAM), Bat. 351, 91405 Orsay Cedex (France)], E-mail: A.Kheifets@anu.edu.au
2008-07-28
We perform calculations of electron impact ionization of noble gas atoms within the distorted wave Born approximation (DWBA) corrected by the Gamow factor (G) to account for the post-collision interaction. We make an extensive comparison with experimental data on He 1s{sup 2}, Ne 2s{sup 2}, 2p{sup 6} and Ar 3p{sup 6} under kinematics characterized by large energy transfer and close to minimum momentum transfer from the projectile to the target. For all atoms, good agreement between theory and experiment is achieved. In the case of Ar, the disagreement of experimental data with theory reported earlier by Catoire et al (2006 J. Phys. B: At. Mol. Opt. Phys. 39 2827) is reconciled.
Electronic Structure Calculations and Adaptation Scheme in Multi-core Computing Environments
Energy Technology Data Exchange (ETDEWEB)
Seshagiri, Lakshminarasimhan; Sosonkina, Masha; Zhang, Zhao
2009-05-20
Multi-core processing environments have become the norm in the generic computing environment and are being considered for adding an extra dimension to the execution of any application. The T2 Niagara processor is a very unique environment where it consists of eight cores having a capability of running eight threads simultaneously in each of the cores. Applications like General Atomic and Molecular Electronic Structure (GAMESS), used for ab-initio molecular quantum chemistry calculations, can be good indicators of the performance of such machines and would be a guideline for both hardware designers and application programmers. In this paper we try to benchmark the GAMESS performance on a T2 Niagara processor for a couple of molecules. We also show the suitability of using a middleware based adaptation algorithm on GAMESS on such a multi-core environment.
Kanungo, Bikash
2016-01-01
We present a computationally efficient approach to perform large-scale all-electron density functional theory calculations by enriching the classical finite element basis with compactly supported atom-centered numerical basis functions that are constructed from the solution of the Kohn-Sham (KS) problem for single atoms. We term these numerical basis functions as enrichment functions, and the resultant basis as the enriched finite element basis. The enrichment functions are compactly supported through the use of smooth cutoff functions, which enhances the conditioning and maintains the locality of the basis. The integrals involved in the evaluation of the discrete KS Hamiltonian and overlap matrix in the enriched finite element basis are computed using an adaptive quadrature grid based on the characteristics of enrichment functions. Further, we propose an efficient scheme to invert the overlap matrix by using a block-wise matrix inversion in conjunction with special reduced-order quadrature rules to transform...
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Chauvin, C
2005-11-15
This thesis is devoted to the definition and the implementation of a multi-resolution method to determine the fundamental state of a system composed of nuclei and electrons. In this work, we are interested in the Density Functional Theory (DFT), which allows to express the Hamiltonian operator with the electronic density only, by a Coulomb potential and a non-linear potential. This operator acts on orbitals, which are solutions of the so-called Kohn-Sham equations. Their resolution needs to express orbitals and density on a set of functions owing both physical and numerical properties, as explained in the second chapter. One can hardly satisfy these two properties simultaneously, that is why we are interested in orthogonal and bi-orthogonal wavelets basis, whose properties of interpolation are presented in the third chapter. We present in the fourth chapter three dimensional solvers for the Coulomb's potential, using not only the preconditioning property of wavelets, but also a multigrid algorithm. Determining this potential allows us to solve the self-consistent Kohn-Sham equations, by an algorithm presented in chapter five. The originality of our method consists in the construction of the stiffness matrix, combining a Galerkin formulation and a collocation scheme. We analyse the approximation properties of this method in case of linear Hamiltonian, such as harmonic oscillator and hydrogen, and present convergence results of the DFT for small electrons. Finally we show how orbital compression reduces considerably the number of coefficients to keep, while preserving a good accuracy of the fundamental energy. (author)
An approach to first principles electronic structure calculation by symbolic-numeric computation
Directory of Open Access Journals (Sweden)
Akihito Kikuchi
2013-04-01
Full Text Available There is a wide variety of electronic structure calculation cooperating with symbolic computation. The main purpose of the latter is to play an auxiliary role (but not without importance to the former. In the field of quantum physics [1-9], researchers sometimes have to handle complicated mathematical expressions, whose derivation seems almost beyond human power. Thus one resorts to the intensive use of computers, namely, symbolic computation [10-16]. Examples of this can be seen in various topics: atomic energy levels, molecular dynamics, molecular energy and spectra, collision and scattering, lattice spin models and so on [16]. How to obtain molecular integrals analytically or how to manipulate complex formulas in many body interactions, is one such problem. In the former, when one uses special atomic basis for a specific purpose, to express the integrals by the combination of already known analytic functions, may sometimes be very difficult. In the latter, one must rearrange a number of creation and annihilation operators in a suitable order and calculate the analytical expectation value. It is usual that a quantitative and massive computation follows a symbolic one; for the convenience of the numerical computation, it is necessary to reduce a complicated analytic expression into a tractable and computable form. This is the main motive for the introduction of the symbolic computation as a forerunner of the numerical one and their collaboration has won considerable successes. The present work should be classified as one such trial. Meanwhile, the use of symbolic computation in the present work is not limited to indirect and auxiliary part to the numerical computation. The present work can be applicable to a direct and quantitative estimation of the electronic structure, skipping conventional computational methods.
Robles, R.; Khanna, S. N.
2009-09-01
First principles electronic structure calculations on a free CrSi12 cluster, a (CrSi12)2 dimer, and CrSi12 clusters supported on Si(111) surfaces have been carried out within a gradient corrected density functional formalism using a supercell approach. The ground state of CrSi12 is a Cr centered hexagonal biprism of Si atoms in which the Cr spin moment is completely quenched. As two CrSi12 motifs are brought together, they form different composite units depending on initial direction of approach and, in most cases, the composite cluster is found to have a net spin moment. Cluster assemblies obtained by depositing CrSi12 motifs on a Si(111) surface exhibit similar finite spin moments for several initial directions of approach. An analysis of the electronic states shows that the origin of the magnetic moment lies in those Cr d -states that do not mix with silicon sp states. The studies suggest the possibility of forming silicon-based magnetic semiconductors through such assemblies.
Magnetic and electronic properties of Cu1-xFexO from first principles calculations
Yang, Hua
2013-01-01
Magnetic and electronic properties of Cu1-xFexO systems with x = 6.25% and 12.5% have been investigated using first principles calculations. The ground state of CuO is an antiferromagnetic insulator. At x = 6.25%, Cu1-xFexO systems with Fe on 2 and 4 substitution positions are half-metallic due to the strong hybridization among Fe, the nearest O and Cu atoms, which may come from the double exchange coupling between Fe2+-O2--Cu2+. At x = 12.5%, Cu 1-xFexO system with Fe on 9-11 position has a strong spin polarization near the Fermi level and the system energy is lowest when the doped two Fe atoms form ferromagnetic configuration. This indicates the two doped Fe atoms prefer to form ferromagnetic configuration in Fe2+-O 2--Cu2+-O2--Fe2+ chains. While in the Fe on 7-11 position, the spin-down Fe-11 3d states have a large spin polarization near the Fermi level when the two doped Fe atoms form antiferromagnetic configuration. It is concluded that the transition metal doping can modify the magnetism and electronic structures of Cu 1-xFexO systems. This journal is © The Royal Society of Chemistry 2013.
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Heilmann, D.B.
2007-02-15
The two-plane HUBBARD model, which is a model for some electronic properties of undoped YBCO superconductors as well as displays a MOTT metal-to-insulator transition and a metal-to-band insulator transition, is studied within Dynamical Mean-Field Theory using HIRSCH-FYE Monte Carlo. In order to find the different transitions and distinguish the types of insulator, we calculate the single-particle spectral densities, the self-energies and the optical conductivities. We conclude that there is a continuous transition from MOTT to band insulator. In the second part, ground state properties of a diagonally disordered HUBBARD model is studied using a generalisation of Path Integral Renormalisation Group, a variational method which can also determine low-lying excitations. In particular, the distribution of antiferromagnetic properties is investigated. We conclude that antiferromagnetism breaks down in a percolation-type transition at a critical disorder, which is not changed appreciably by the inclusion of correlation effects, when compared to earlier studies. Electronic and excitation properties at the system sizes considered turn out to primarily depend on the geometry. (orig.)
Egami, Yoshiyuki; Iwase, Shigeru; Tsukamoto, Shigeru; Ono, Tomoya; Hirose, Kikuji
2015-09-01
We develop a first-principles electron-transport simulator based on the Lippmann-Schwinger (LS) equation within the framework of the real-space finite-difference scheme. In our fully real-space-based LS (grid LS) method, the ratio expression technique for the scattering wave functions and the Green's function elements of the reference system is employed to avoid numerical collapse. Furthermore, we present analytical expressions and/or prominent calculation procedures for the retarded Green's function, which are utilized in the grid LS approach. In order to demonstrate the performance of the grid LS method, we simulate the electron-transport properties of the semiconductor-oxide interfaces sandwiched between semi-infinite jellium electrodes. The results confirm that the leakage current through the (001 )Si -SiO2 model becomes much larger when the dangling-bond state is induced by a defect in the oxygen layer, while that through the (001 )Ge -GeO2 model is insensitive to the dangling bond state.
Directory of Open Access Journals (Sweden)
Qiushi Zheng
2017-02-01
Full Text Available Vanadium-bearing muscovite is the most valuable component of stone coal, which is a unique source of vanadium manufacture in China. Numbers of experimental studies have been carried out to destroy the carrier muscovite’s structure for efficient extraction of vanadium. Hence, the vanadium location is necessary for exploring the essence of vanadium extraction. Although most infer that vanadium may substitute for trivalent aluminium (Al as the isomorphism in muscovite for the similar atomic radius, there is not enough experimental evidence and theoretical supports to accurately locate the vanadium site in muscovite. In this study, the muscovite model and optimal location of vanadium were calculated by density functional theory (DFT. We find that the vanadium prefers to substitute for the hexa-coordinated aluminum of muscovite for less deformation and lower substitution energy. Furthermore, the local geometry and relative electronic properties were calculated in detail. The basal theoretical research of muscovite contained with vanadium are reported for the first time. It will make a further influence on the technology development of vanadium extraction from stone coal.
Greenman, Loren; Lucchese, Robert R.; McCurdy, C. William
2017-11-01
The complex Kohn variational method for electron-polyatomic-molecule scattering is formulated using an overset-grid representation of the scattering wave function. The overset grid consists of a central grid and multiple dense atom-centered subgrids that allow the simultaneous spherical expansions of the wave function about multiple centers. Scattering boundary conditions are enforced by using a basis formed by the repeated application of the free-particle Green's function and potential Ĝ0+V ̂ on the overset grid in a Born-Arnoldi solution of the working equations. The theory is shown to be equivalent to a specific Padé approximant to the T matrix and has rapid convergence properties, in both the number of numerical basis functions employed and the number of partial waves employed in the spherical expansions. The method is demonstrated in calculations on methane and CF4 in the static-exchange approximation and compared in detail with calculations performed with the numerical Schwinger variational approach based on single-center expansions. An efficient procedure for operating with the free-particle Green's function and exchange operators (to which no approximation is made) is also described.
Calculating Electron Drift Velocity and Development of the ND Cube Detector
Delgado, Lauren
2017-09-01
Active-target detectors are crucial for reactions with radioactive beams because of their high efficiency and good energy resolution. Their significant amount of target material enhances the ability to perform experiments at lower beam rates. At University of Notre Dame, we are developing an active-target time-projection chamber called the ND Cube that will image charged-particle tracks. To understand properties of the detector such as electron drift velocity and straggling in the detector gas, calculations were obtained for a He-CO2 mixture as a function of electric field and pressure. Higher electric field strengths and lower pressures produced higher drift velocities. Increased pressures minimized both longitudinal and transverse straggling whereas electric field strength had no direct effect on straggling in either direction. Additionally, the field cage of the detector was completed and electrical feedthroughs were designed and constructed. The completion of the field cage included the assembly and testing of its resistor chain. The cage will be tested in experimental conditions and used in future measurements of drift velocity and straggling. Experimental data will be compared with our calculated results and aid our understanding of the detector design. University of Notre Dame, Vassar College, and NSF.
Mondal, Abhisek; Datta, Saumen
2017-06-01
Hydrogen bond plays a unique role in governing macromolecular interactions with exquisite specificity. These interactions govern the fundamental biological processes like protein folding, enzymatic catalysis, molecular recognition. Despite extensive research work, till date there is no proper report available about the hydrogen bond's energy surface with respect to its geometric parameters, directly derived from proteins. Herein, we have deciphered the potential energy landscape of hydrogen bond directly from the macromolecular coordinates obtained from Protein Data Bank using quantum mechanical electronic structure calculations. The findings unravel the hydrogen bonding energies of proteins in parametric space. These data can be used to understand the energies of such directional interactions involved in biological molecules. Quantitative characterization has also been performed using Shannon entropic calculations for atoms participating in hydrogen bond. Collectively, our results constitute an improved way of understanding hydrogen bond energies in case of proteins and complement the knowledge-based potential. Proteins 2017; 85:1046-1055. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.
Energy Technology Data Exchange (ETDEWEB)
Cullen, D.E.
1994-08-01
The computer code WALKMAN performs electron single collision elastic scattering Monte Carlo calculations in spherical or planar geometry. It is intended as a research tool to obtain results that can be compared to the results of condensed history calculations. This code is designed to be self documenting, in the sense that the latest documentation is included as comment lines at the beginning of the code. Printed documentation, such as this document, is periodically published and consists mostly of a copy of the comment lines from the code. The user should be aware that the comment lines within the code are continually updated to reflect the most recent status of the code and these comments should always be considered to be the most recent documentation for the code and may supersede published documentation, such as this document. Therefore, the user is advised to always read the documentation within the actual code. The remainder of this report consists of example results and a listing of the documentation which appears at the beginning of the code.
Gamayunov, K. V.; Khazanov, G. V.
2007-01-01
We consider the effect of oblique EMIC waves on relativistic electron scattering in the outer radiation belt using simultaneous observations of plasma and wave parameters from CRRES. The main findings can be s ummarized as follows: 1. In 1comparison with field-aligned waves, int ermediate and highly oblique distributions decrease the range of pitc h-angles subject to diffusion, and reduce the local scattering rate b y an order of magnitude at pitch-angles where the principle absolute value of n = 1 resonances operate. Oblique waves allow the absolute va lue of n > 1 resonances to operate, extending the range of local pitc h-angle diffusion down to the loss cone, and increasing the diffusion at lower pitch angles by orders of magnitude; 2. The local diffusion coefficients derived from CRRES data are qualitatively similar to the local results obtained for prescribed plasma/wave parameters. Conseq uently, it is likely that the bounce-averaged diffusion coefficients, if estimated from concurrent data, will exhibit the dependencies similar to those we found for model calculations; 3. In comparison with f ield-aligned waves, intermediate and highly oblique waves decrease th e bounce-averaged scattering rate near the edge of the equatorial lo ss cone by orders of magnitude if the electron energy does not excee d a threshold (approximately equal to 2 - 5 MeV) depending on specified plasma and/or wave parameters; 4. For greater electron energies_ ob lique waves operating the absolute value of n > 1 resonances are more effective and provide the same bounce_averaged diffusion rate near the loss cone as fiel_aligned waves do.
DFT calculations on electronic properties of ZnO thin films deposited by spray pyrolysis
Energy Technology Data Exchange (ETDEWEB)
Cordeiro, J.M.; Reynoso, V.C.; Azevedo, D.H.M. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), SP (Brazil)
2016-07-01
Full text: Introduction - Thin films of Zinc oxide (ZnO) has a wide range of technological applications, as transparent conducting electrodes in solar cells, flat panel displays, and sensors, for example. More recently applications in optoelectronics, like light emitter diodes and laser diodes, due to its large band gap, are been explored. Studies of ZnO thin films are important for these applications. Methodology - In this study thin films of ZnO have been deposited by spray pyrolysis on glass substrate. The films were characterized by XRD and UV-VIS techniques and the electronic properties as a function of the film thickness have been investigated by DFT calculations with B3LYP hybrid potential implemented in the CRYSTAL09 code. Results - The diffractograms obtained for the ZnO thin films as a function of the thickness are shown. The films exhibit a hexagonal wurtzite structure with preferred c-axis orientation in (002) direction of ZnO crystal. A quantum mechanical approach based on the periodic Density Functional Theory (DFT), with B3LYP hybrid potential was used to investigate the electronic structure of the films as a function of the thickness. The CRYSTAL09 code has been used for the calculations on the wurtzite hexagonal structure of ZnO - spatial group P63mc. For optimizing the geometry of the pure ZnO crystal, the experimental lattice parameters were got as follows: a= 0.325 nm, b= 0.325 nm, c= 0.5207 nm with c/a= 1.602. Considering to the calculations of the band structure, it is suggested that the semiconducting properties of ZnO arises from the overlapping of the 4s orbital of the conducting band of Zn and the 2p orbital of the top of valence band of O. Conclusions - The structure of ZnO thin film deposited on glass substrate present preferential orientation in (002) direction. Variation in the optical properties as a function of the film thickness was observed. The band gap energy was determined from optical analysis to be ∼ 3.27 eV. The refractive
DEFF Research Database (Denmark)
Shim, Irene; Pelino, Mario; Gingerich, Karl A.
1992-01-01
In the present work we present results of all electron ab initio multiconfiguration self-consistent-field calculations of eight electronic states of the molecule YC. Also reported are the calculated spectroscopic constants. The predicted electronic ground state is 4PI, but this state is found......, and they hardly contribute to the bonding. The chemical bond in the YC molecule is polar with charge transfer from Y to C giving rise to a dipole moment of 3.90 D at 3.9 a.u. in the 4PI ground state. Mass spectrometric equilibrium investigations in the temperature range 2365-2792 K have resulted...
Gao, Ting; Sun, Shi-Ling; Shi, Li-Li; Li, Hui; Li, Hong-Zhi; Su, Zhong-Min; Lu, Ying-Hua
2009-05-14
Support vector machines (SVMs), as a novel type of learning machine, has been very successful in pattern recognition and function estimation problems. In this paper we introduce least-squares (LS) SVMs to improve the calculation accuracy of density functional theory. As a demonstration, this combined quantum mechanical calculation with LS-SVM correction approach has been applied to evaluate the electronic excitation energies of 160 organic molecules. The newly introduced LS-SVM approach reduces the root-mean-square deviation of the calculated electronic excitation energies of 160 organic molecules from 0.32 to 0.11 eV for the B3LYP/6-31G(d) calculation. Thus, the LS-SVM correction on top of B3LYP/6-31G(d) is a better method to correct electronic excitation energies and can be used as the approximation of experimental results which are impossible to obtain experimentally.
Assouad type dimensions for partially affine sponges
Howroyd, Douglas
2016-01-01
Recently self-affine sponges have been shown to be interesting examples and counter-examples to several previously open problems. One class of recently discovered sponges are partially affine Bedford-McMullen sponges whose Assouad type dimensions cannot be calculated like the dimensions of regular Bedford-McMullen sponges are. We calculate the Assouad type dimensions for such partially affine sponges and discuss some of their more subtle details.
Levashov, P R; Sin'ko, G V; Smirnov, N A; Minakov, D V; Shemyakin, O P; Khishchenko, K V
2010-12-22
In the present work, we compare the thermal contribution of electrons to thermodynamic functions of metals in different models at high densities and electron temperatures. One of the theoretical approaches, the full-potential linear-muffin-tin-orbital method, treats all electrons in the framework of density functional theory (DFT). The other approach, VASP, uses projector-augmented-wave pseudopotentials for the core electrons and considers the valent electrons also in the context of DFT. We analyze the limitations of the pseudopotential approach and compare the DFT results with a finite-temperature Thomas-Fermi model and two semiempirical equations of state.
Energy Technology Data Exchange (ETDEWEB)
Levashov, P R; Minakov, D V; Shemyakin, O P; Khishchenko, K V [Joint Institute for High Temperatures, Russian Academy of Sciences, Izhorskaya 13 Building 2, Moscow 125412 (Russian Federation); Sin' ko, G V; Smirnov, N A, E-mail: pasha@ihed.ras.r [Russian Federal Nuclear Center-Zababakhin All-Russia Research Institute of Technical Physics, Snezhinsk 456770, Chelyabinsk region (Russian Federation)
2010-12-22
In the present work, we compare the thermal contribution of electrons to thermodynamic functions of metals in different models at high densities and electron temperatures. One of the theoretical approaches, the full-potential linear-muffin-tin-orbital method, treats all electrons in the framework of density functional theory (DFT). The other approach, VASP, uses projector-augmented-wave pseudopotentials for the core electrons and considers the valent electrons also in the context of DFT. We analyze the limitations of the pseudopotential approach and compare the DFT results with a finite-temperature Thomas-Fermi model and two semiempirical equations of state.
Relativistic R -matrix calculations for the electron-impact excitation of neutral molybdenum
Smyth, R. T.; Johnson, C. A.; Ennis, D. A.; Loch, S. D.; Ramsbottom, C. A.; Ballance, C. P.
2017-10-01
A recent PISCES-B Mod experiment [Nishijima et al., J. Phys. B 43, 225701 (2010), 10.1088/0953-4075/43/22/225701] has revealed up to a factor of 5 discrepancy between measurement and the two existing theoretical models [Badnell et al., J. Phys. B 29, 3683 (1996), 10.1088/0953-4075/29/16/014; Bartschat et al., J. Phys. B 35, 2899 (2002), 10.1088/0953-4075/35/13/305], providing important diagnostics for Mo i. In the following paper we address this issue by employing a relativistic atomic structure and R -matrix scattering calculations to improve upon the available models for future applications and benchmark results against a recent Compact Toroidal Hybrid experiment [Hartwell et al., Fusion Sci. Technol. 72, 76 (2017), 10.1080/15361055.2017.1291046]. We determine the atomic structure of Mo i using grasp0, which implements the multiconfigurational Dirac-Fock method. Fine structure energies and radiative transition rates are presented and compared to existing experimental and theoretical values. The electron-impact excitation of Mo i is investigated using the relativistic R -matrix method and the parallel versions of the Dirac atomic R -matrix codes. Electron-impact excitation cross sections are presented and compared to the few available theoretical cross sections. Throughout, our emphasis is on improving the results for the z 1,2,3o5P →a S52,z 2,3,4o7P → a S73 and y 2,3,4o7P → a S73 electric dipole transitions of particular relevance for diagnostic work.
Directory of Open Access Journals (Sweden)
Sanjeev K. Gupta
2013-03-01
Full Text Available In the frame work of density functional theoretical calculations, the electronic and lattice dynamical properties of graphene (multilayers and supercell have been systematically investigated and analyzed using the plane wave pseudopotentials within the generalized gradient approximation and local density approximation functional. We have also studied the functionalization of graphene by adsorption and absorption of transition metals like Al and Ag. We find that the electronic properties exhibit large sensitivity to the number of layers and doping. The Al and Ag doped graphene exhibits peak at Fermi level in the density of states arising from the flat bands near Fermi level. The bonding of metal atoms and graphene leads to a charge transfer between them and consequently shift Fermi level with respect to the conical point at K-point. The adsorption of Ag/Al atoms suggests an effective interaction between the adatoms and graphene layers without disturbing the original graphene structure of lower graphene layers. Compared to single layer graphene, the optical phonon E2g mode and out of plane ZA mode at Γ-point splits in the bi-, tri- and four- layer graphene. We observe a shift for highest optical branch at Dirac K- point. We find that the different derivatives of graphene have different phonon dispersion relations. We demonstrate that there is removal of degeneracy of ZO/ZA modes at K- point with transition metal doping. The highest optical phonon branch becomes flat at Dirac point with doping of transition metals. Our study points that the substituted graphene sheets can have potential applications in ordered-disordered separated quantum films with two to four layers of atoms and new nano devices using graphene.
Gandhi, Om P.; Kang, Gang
2001-11-01
This paper illustrates the use of the impedance method to calculate the electric fields and current densities induced in millimetre resolution anatomic models of the human body, namely an adult and 10- and 5-year-old children, for exposure to nonuniform magnetic fields typical of two assumed but representative electronic article surveillance (EAS) devices at 1 and 30 kHz, respectively. The devices assumed for the calculations are a solenoid type magnetic deactivator used at store checkouts and a pass-by panel-type EAS system consisting of two overlapping rectangular current-carrying coils used at entry and exit from a store. The impedance method code is modified to obtain induced current densities averaged over a cross section of 1 cm2 perpendicular to the direction of induced currents. This is done to compare the peak current densities with the limits or the basic restrictions given in the ICNIRP safety guidelines. Because of the stronger magnetic fields at lower heights for both the assumed devices, the peak 1 cm2 area-averaged current densities for the CNS tissues such as the brain and the spinal cord are increasingly larger for smaller models and are the highest for the model of the 5-year-old child. For both the EAS devices, the maximum 1 cm2 area-averaged current densities for the brain of the model of the adult are lower than the ICNIRP safety guideline, but may approach or exceed the ICNIRP basic restrictions for models of 10- and 5-year-old children if sufficiently strong magnetic fields are used.
Energy Technology Data Exchange (ETDEWEB)
Huang, Bo [School of Material Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China); Duan, Yong-Hua, E-mail: duanyh@kmust.edu.cn [School of Material Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China); Key Lab of Advance Materials in Rare & Precious and Nonferrous Metals, Ministry of Education, Kunming 650093 (China); Sun, Yong [School of Material Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China); Key Lab of Advance Materials in Rare & Precious and Nonferrous Metals, Ministry of Education, Kunming 650093 (China); Peng, Ming-Jun; Chen, Shuai [School of Material Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China)
2015-06-25
Highlights: • The band gaps for CaB{sub 6}, SrB{sub 6} and BaB{sub 6} depend sensitively on the values of lattice constant a and positional parameter z. • The order in elastic anisotropy is CaB{sub 6} > SrB{sub 6} > BaB{sub 6}. • There are LO/TO splitting lines in the range of 5–10 THz at G point. - Abstract: The electronic structures, mechanical and thermodynamic properties of alkaline-earth hexaborides MB{sub 6} (M = Ca, Sr or Ba) are calculated from first principles using density functional theory combined with the quasi-harmonic approximation. These three alkaline-earth hexaborides are semiconductors with a slightly increased trend for their band gaps as M orders from Ca to Ba. Their band gaps depend sensitively on the values of lattice constant a and internal parameter z. The polycrystalline values of the elastic constants and bulk, shear and Young’s moduli are consistent with those determined experimentally. All alkaline-earth hexaborides have strongly anisotropic elastic properties in the order of CaB{sub 6} > SrB{sub 6} > BaB{sub 6}. By using the phonon calculations, the thermodynamic properties are investigated. The obtained phonon dispersion relations for CaB{sub 6}, SrB{sub 6}, and BaB{sub 6} show similar features and there are LO/TO splitting lines in the range of 5–10 THz. Finally, the thermal conductivities of CaB{sub 6}, SrB{sub 6} and BaB{sub 6} are evaluated via Clarke’s model and Cahill’s model.
Li, Zi; Zhang, Xu; Lu, Gang
2011-12-01
A Fortran program is developed to calculate charge carrier (electron or hole) mobility in disordered semiconductors from first-principles. The method is based on non-adiabatic ab initio molecular dynamics and static master equation, treating dynamic and static disorder on the same footing. We have applied the method to calculate the hole mobility in disordered poly(3-hexylthiophene) conjugated polymers as a function of temperature and electric field and obtained excellent agreements with experimental results. The program could be used to explore structure-mobility relation in disordered semiconducting polymers/organic semiconductors and aid rational design of these materials. Program summaryProgram title: FPMu Catalogue identifier: AEJV_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEJV_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 788 580 No. of bytes in distributed program, including test data, etc.: 8 433 024 Distribution format: tar.gz Programming language: Fortran 90 Computer: Any architecture with a Fortran 90 compiler Operating system: Linux, Windows RAM: Proportional to the system size, in our example, 1.2 GB Classification: 7.9 Nature of problem: Determine carrier mobility from first-principles in disordered semiconductors as a function of temperature, electric field and carrier concentration. Solution method: Iteratively solve master equation with carrier state energy and transition rates determined from first-principles. Restrictions: Mobility for disordered semiconductors where the carrier wave-functions are localized and the carrier transport is due to phonon-assisted hopping mechanism. Running time: Depending on the system size (about an hour for the example here).
Energy Technology Data Exchange (ETDEWEB)
Jannik, Tim [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Stagich, Brooke [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
2015-08-28
The U.S. Environmental Protection Agency (EPA) requested an external, independent verification study of their updated “Preliminary Remediation Goals for Radionuclides” (PRG) electronic calculator. The calculator provides PRGs for radionuclides that are used as a screening tool at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and Resource Conservation and Recovery Act (RCRA) sites. These risk-based PRGs establish concentration limits under specific exposure scenarios. The purpose of this verification study is to determine that the calculator has no inherit numerical problems with obtaining solutions as well as to ensure that the equations are programmed correctly. There are 167 equations used in the calculator. To verify the calculator, all equations for each of seven receptor types (resident, construction worker, outdoor and indoor worker, recreator, farmer, and composite worker) were hand calculated using the default parameters. The same four radionuclides (Am-241, Co-60, H-3, and Pu-238) were used for each calculation for consistency throughout.
Sugawara, Hirotake
2017-04-01
A propagator method (PM), a numerical technique to solve the Boltzmann equation (BE) for the electron velocity or energy distribution function (EVDF/EEDF) of electron swarms in gases, was customized to obtain the equilibrium solution quickly. The PM calculates the number of electrons in cells defined in velocity space using an operator called the propagator or Green’s function. The propagator represents the intercellular transfer of electrons corresponding to the electron velocity change due to the acceleration by the electric field and the collisional events with gas molecules. The relaxation of the EVDF to its drift equilibrium solution proceeds with iterative propagator operations for the EVDF. Merits of the PM are that the series expansion of the EVDF as done in the BE analyses is not required and that time evolution of the electron swarm can be observed if necessary. On the other hand, in case only the equilibrium solution of the EVDF is wanted, the relaxation can be accelerated numerically. A demonstration achieved a shortening of the computational time by about three orders of magnitude. Furthermore, this scheme was applied to calculations of a set of electron transport parameters required in fluid-model simulations, i.e. the effective ionization frequency, the centroid drift velocity and the longitudinal diffusion coefficient, using the zeroth-, first- and second-order moment equations derived from the BE. A detailed description on the PM calculation was presented.
Electronic spectra and DFT calculations of some pyrimido[1,2-a]benzimidazole derivatives.
Elshakre, Mohamed E; Moustafa, H; Hassaneen, Huwaida M E; Moussa, Abdelrahim Z
2015-06-15
Ground state properties of 2,4-diphenyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine, compound 1, and its derivatives are investigated experimentally and theoretically in Dioxane and DMF. The calculations show that all the studied compounds (1-7) are non-planar, resulting in a significant impact on the electronic and structural properties. The ground state properties of compounds 1-7 at B3LYP/6-311G (d, p) show that compound 5 has the lowest EHOMO, ELUMO, and ΔE indicating highest reactivity. Compound 7 is found to have the highest polarity. The observed UV spectra in Dioxane and DMF of compounds 1-4 show 2 bands, while compounds 5-7 show 4 bands in both solvents. Band maxima (λmax) and intensities of the spectra are found to have solvent dependence reflected as blue and red shifts. The theoretical spectra computed at TD-B3LYP/6-311G (d, p) in gas phase, Dioxane and DMF indicate a good agreement with the observed spectra. Copyright © 2015 Elsevier B.V. All rights reserved.
Structures and electronic properties of germanium-doped Ni n clusters, n = 13-23
Song, Wei; Li, Hua-qiang; He, Chao-zheng; Zhang, Wei
2017-11-01
The magnetic property and electronic properties such as binding energy, charge transfer, ionization potential and electron affinity of the Ni n-1Ge ( n = 13-23) neutral and ionic clusters have been studied using the density functional theory calculations with the PBE exchange-correlation energy functional. The calculated total magnetic moments decrease with the addition of Ge atom. Both the calculated ionization potential and electron affinity exhibit an oscillating behavior as the cluster size increases.
Yost, Dillon C.; Yao, Yi; Kanai, Yosuke
2017-09-01
In ion irradiation processes, electronic stopping power describes the energy transfer rate from the irradiating ion to the target material's electrons. Due to the scarcity and significant uncertainties in experimental electronic stopping power data for materials beyond simple solids, there has been growing interest in the use of first-principles theory for calculating electronic stopping power. In recent years, advances in high-performance computing have opened the door to fully first-principles nonequilibrium simulations based on real-time time-dependent density functional theory (RT-TDDFT). While it has been demonstrated that the RT-TDDFT approach is capable of predicting electronic stopping power for a wide range of condensed matter systems, there has yet to be an exhaustive examination of the physical and numerical approximations involved and their effects on the calculated stopping power. We discuss the results of such a study for crystalline silicon with protons as irradiating ions. We examine the influences of key approximations in RT-TDDFT nonequilibrium simulations on the calculated electronic stopping power, including approximations related to basis sets, finite size effects, exchange-correlation approximation, pseudopotentials, and more. Finally, we propose a simple and efficient correction scheme to account for the contribution from core-electron excitations to the stopping power, as it was found to be significant for large proton velocities.
Directory of Open Access Journals (Sweden)
M. V. Tchernycheva
2017-01-01
Full Text Available Subject of Research. The paper deals with development outcomes for creation method of one-electron wave functions of complex atoms, relatively simple, symmetrical for all atom electrons and free from hard computations. The accuracy and resource intensity of the approach are focused on systematic calculations of cross sections and rate constants of elementary processes of inelastic collisions of atoms or molecules with electrons (ionization, excitation, excitation transfer, and others. Method. The method is based on a set of two iterative processes. At the first iteration step the Schrödinger equation was solved numerically for the radial parts of the electron wave functions in the potential of the atomic core self-consistent field. At the second iteration step the new approximationfor the atomic core field is created that uses found solutions for all one-electron wave functions. The solution optimization for described multiparameter problem is achieved by the use of genetic algorithm. The suitability of the developed method was verified by comparing the calculation results with numerous data on the energies of atoms in the ground and excited states. Main Results. We have created the run-time version of the program for creation of sets of one-electron wave functions and calculation of the cross sections and constants of collisional transition rates in the first Born approximation. The priori available information about binding energies of the electrons for any many-particle system for creation of semi-empirical refined solutions for the one-electron wave functions can be considered at any step of this procedure. Practical Relevance. The proposed solution enables a simple and rapid preparation of input data for the numerical simulation of nonlocal gas discharge plasma. The approach is focused on the calculation of discharges in complex gas mixtures requiring inclusion in the model of a large number of elementary collisional and radiation
Bisetti, Fabrizio
2012-12-01
Simulations of ion and electron transport in flames routinely adopt plasma fluid models, which require transport coefficients to compute the mass flux of charged species. In this work, the mobility and diffusion coefficient of thermal electrons in atmospheric premixed methane/air flames are calculated and analyzed. The electron mobility is highest in the unburnt region, decreasing more than threefold across the flame due to mixture composition effects related to the presence of water vapor. Mobility is found to be largely independent of equivalence ratio and approximately equal to 0.4m 2V -1s -1 in the reaction zone and burnt region. The methodology and results presented enable accurate and computationally inexpensive calculations of transport properties of thermal electrons for use in numerical simulations of charged species transport in flames. © 2012 The Combustion Institute.
Shi, Guangsha
Solar electricity is a reliable and environmentally friendly method of sustainable energy production and a realistic alternative to conventional fossil fuels. Moreover, thermoelectric energy conversion is a promising technology for solid-state refrigeration and efficient waste-heat recovery. Predicting and optimizing new photovoltaic and thermoelectric materials composed of Earth-abundant elements that exceed the current state of the art, and understanding how nanoscale structuring and ordering improves their energy conversion efficiency pose a challenge for materials scientists. I approach this challenge by developing and applying predictive high-performance computing methods to guide research and development of new materials for energy-conversion applications. Advances in computer-simulation algorithms and high-performance computing resources promise to speed up the development of new compounds with desirable properties and significantly shorten the time delay between the discovery of new materials and their commercial deployment. I present my calculated results on the extraordinary properties of nanostructured semiconductor materials, including strong visible-light absorbance in nanoporous silicon and few-layer SnSe and GeSe. These findings highlight the capability of nanoscale structuring and ordering to improve the performance of Earth-abundant materials compared to their bulk counterparts for solar-cell applications. I also successfully identified the dominant mechanisms contributing to free-carrier absorption in n-type silicon. My findings help evaluate the impact of the energy loss from this absorption mechanism in doped silicon and are thus important for the design of silicon solar cells. In addition, I calculated the thermoelectric transport properties of p-type SnSe, a bulk material with a record thermoelectric figure of merit. I predicted the optimal temperatures and free-carrier concentrations for thermoelectric energy conversion, as well the
Directory of Open Access Journals (Sweden)
H Hosseinkhani
2016-09-01
Full Text Available In this paper, considering the plasma electronic exchange intraction effects, first, Thomas–Fermi equation has been solved numerically. Then, employing the results of these equations, the amount of exchange corrections for pressure and internal energy of the plasma (electron gas with specific atomic number has been calculated based on variation of plasma density and temperature. The results of the calculations can be used in both quantitative and qualitative description of changing the phase of matter in high temperature and density, encountered with in theoretical and experimental studies of inertial fusion and astro physical phenomena as well.
Blokhin, A I
2001-01-01
In this paper the results of physical verification for the BOFOD photonuclear data files are reported, available for the uranium isotopes U sup 2 sup 3 sup 5 , U sup 2 sup 3 sup 8. These results were compared with calculated data by the parameterization driven model of photonuclear reaction and experimental data. Experimental data of photoneutron yields from surface of uranium sphere irradiated by 28 MeV electrons are used for a verification. Both calculations have been carried out with the RTS and T general purpose Monte Carlo code with detailed electron-photon-nucleon transport simulation using the ENDF/B-VI and EPDL evaluated data libraries.
Alparone, A.
2012-09-01
Vertical electronic transitions to singlet valence states of an antipsychotic drug, Risperidone (Risperdal), in its neutral, mono-, and diprotonated forms have been calculated within the time-dependent density functional theory using the PBE0 hybrid functional with the 6-31+G* basis set. The results of the computations show that the lowest-energy allowed π-π* electronic excitation is affected by protonation effects, the spectral shifts of this transition being potentially useful to individuate the different forms of risperidone
Energy Technology Data Exchange (ETDEWEB)
Wang, Lin-Wang; Zhao, Zhengji; Meza, Juan; Wang, Lin-Wang
2008-07-11
We present a new linear scaling ab initio total energy electronic structure calculation method based on the divide-and-conquer strategy. This method is simple to implement, easily to parallelize, and produces very accurate results when compared with the direct ab initio method. The method has been tested using up to 8,000 processors, and has been used to calculate nanosystems up to 15,000 atoms.
Dey, Tanusri; Praveena, Koduru Sri Shanthi; Pal, Sarbani; Mukherjee, Alok Kumar
2017-06-01
Three oxime ether derivatives, (E)-3-methoxy-4-(prop-2-ynyloxy)-benzaldehyde-O-prop-2-ynyl-oxime (C14H13NO3) (2), benzophenone-O-prop-2-ynyl-oxime (C16H13NO) (3) and (E)-2-chloro-6-methylquinoline-3-carbaldehyde-O-prop-2-ynyl-oxime (C14H11ClN2O) (4), have been synthesized and their crystal structures have been determined. The DFT optimized molecular geometries in 2-4 agree closely with those obtained from the crystallographic study. An interplay of intermolecular Csbnd H⋯O, Csbnd H⋯N, Csbnd H⋯Cl and Csbnd H···π(arene) hydrogen bonds and π···π interactions assembles molecules into a 2D columnar architecture in 2, a 1D molecular ribbon in 3 and a 3D framework in 4. Hirshfeld surface analysis showed that the structures of 2 and 3 are mainly characterized by H⋯H, H⋯C and H⋯O contacts but some contribution of H⋯N and H⋯Cl contacts is also observed in 4. Hydrogen-bond based interactions in 2-4 have been complemented by calculating molecular electrostatic potential (MEP) surfaces. The electronic structures of molecules reveal that the estimated band gap in 3, in which both aldehyde hydrogen atoms of formaldehyde-O-prop-2-ynyl-oxime (1) have been substituted by two benzene rings, is higher than that of 2 and 4 with only one aldehyde hydrogen atom replaced.
Energy Technology Data Exchange (ETDEWEB)
Vazart, Fanny; Latouche, Camille; Skouteris, Dimitrios; Barone, Vincenzo [Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56125 Pisa (Italy); Balucani, Nadia [Dipartimento di Chimica, Biologia e Biotecnologie, Universitá degli Studi di Perugia, Via Elce di Sotto 8, I-06123 Perugia (Italy)
2015-09-10
New insights into the formation of interstellar cyanomethanimine, a species of great relevance in prebiotic chemistry, are provided by electronic structure and kinetic calculations for the reaction CN + CH{sub 2} = NH. This reaction is a facile formation route of Z,E-C-cyanomethanimine, even under the extreme conditions of density and temperature typical of cold interstellar clouds. E-C-cyanomethanimine has been recently identified in Sgr B2(N) in the Green Bank Telescope (GBT) PRIMOS survey by P. Zaleski et al. and no efficient formation routes have been envisaged so far. The rate coefficient expression for the reaction channel leading to the observed isomer E-C-cyanomethanimine is 3.15 × 10-10 × (T/300){sup 0.152} × e{sup (−0.0948/T)}. According to the present study, the more stable Z-C-cyanomethanimine isomer is formed with a slightly larger yield (4.59 × 10{sup −10} × (T/300){sup 0.153} × e{sup (−0.0871/T)}. As the detection of E-isomer is favored due to its larger dipole moment, the missing detection of the Z-isomer can be due to the sensitivity limit of the GBT PRIMOS survey and the detection of the Z-isomer should be attempted with more sensitive instrumentation. The CN + CH{sub 2} = NH reaction can also play a role in the chemistry of the upper atmosphere of Titan where the cyanomethanimine products can contribute to the buildup of the observed nitrogen-rich organic aerosols that cover the moon.
ELECTRONIC-STRUCTURE OF THE LEAD MONOXIDES - BAND-STRUCTURE CALCULATIONS AND PHOTOELECTRON-SPECTRA
TERPSTRA, HJ; DEGROOT, RA; HAAS, C
1995-01-01
PbO is a layer compound which exists in two polymorphic forms, a red tetragonal (alpha) and a yellow orthorhombic (beta) modification. Ab initio band-structure calculations are presented for both phases. The calculated energy gaps are in agreement with optical data. The band-structure calculations
Zhang, Bintuan; Dang, Bingrong; Wang, Zhuanzi; Wei, Wei; Li, Wenjian
2013-10-01
The skin tissue-equivalent slab reported in the International Commission on Radiological Protection (ICRP) Publication 116 to calculate the localised skin dose conversion coefficients (LSDCCs) was adopted into the Monte Carlo transport code Geant4. The Geant4 code was then utilised for computation of LSDCCs due to a circular parallel beam of monoenergetic electrons, protons and alpha particles electrons and alpha particles are found to be in good agreement with the results using the MCNPX code of ICRP 116 data. The present work thus validates the LSDCC values for both electrons and alpha particles using the Geant4 code.
Energy Technology Data Exchange (ETDEWEB)
Ghosh, Binita [St. Paul’s Cathedral Mission College, 33/1Raja Rammohan Roy Road, Kolkata 700009 (India); Halder, Saswata; Sinha, T. P. [Department of Physics, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata 700009 (India); Das, Sayantani [Department of Physics, University of Calcutta, 92 Acharya Prafulla Chandra Road, Kolkata 700009 (India)
2016-05-23
Europium-doped luminescent barium samarium tantalum oxide Ba{sub 2}SmTaO{sub 6} (BST) has been investigated by first-principles calculation, and the crystal structure, electronic structure, and optical properties of pure BST and Eu-doped BST have been examined and compared. Based on the calculated results, the luminescence properties and mechanism of Eu-doped BST has been discussed. In the case of Eu-doped BST, there is an impurity energy band at the Fermi level, which is formed by seven spin up energy levels of Eu and act as the luminescent centre, which is evident from the band structure calculations.
Muir, B R; Rogers, D W O
2013-12-01
To investigate recommendations for reference dosimetry of electron beams and gradient effects for the NE2571 chamber and to provide beam quality conversion factors using Monte Carlo simulations of the PTW Roos and NE2571 ion chambers. The EGSnrc code system is used to calculate the absorbed dose-to-water and the dose to the gas in fully modeled ion chambers as a function of depth in water. Electron beams are modeled using realistic accelerator simulations as well as beams modeled as collimated point sources from realistic electron beam spectra or monoenergetic electrons. Beam quality conversion factors are calculated with ratios of the doses to water and to the air in the ion chamber in electron beams and a cobalt-60 reference field. The overall ion chamber correction factor is studied using calculations of water-to-air stopping power ratios. The use of an effective point of measurement shift of 1.55 mm from the front face of the PTW Roos chamber, which places the point of measurement inside the chamber cavity, minimizes the difference between R50, the beam quality specifier, calculated from chamber simulations compared to that obtained using depth-dose calculations in water. A similar shift minimizes the variation of the overall ion chamber correction factor with depth to the practical range and reduces the root-mean-square deviation of a fit to calculated beam quality conversion factors at the reference depth as a function of R50. Similarly, an upstream shift of 0.34 rcav allows a more accurate determination of R50 from NE2571 chamber calculations and reduces the variation of the overall ion chamber correction factor with depth. The determination of the gradient correction using a shift of 0.22 rcav optimizes the root-mean-square deviation of a fit to calculated beam quality conversion factors if all beams investigated are considered. However, if only clinical beams are considered, a good fit to results for beam quality conversion factors is obtained without
Ramanantoanina, Harry; Daul, Claude
2017-08-01
The ligand field density functional theory (LFDFT) algorithm is extended to treat the electronic structure and properties of systems with three-open-shell electron configurations, exemplified in this work by the calculation of the core and semi-core 1s, 2s, and 3s one-electron excitations in compounds containing transition metal ions. The work presents a model to non-empirically resolve the multiplet energy levels arising from the three-open-shell systems of non-equivalent ns, 3d, and 4p electrons and to calculate the oscillator strengths corresponding to the electric-dipole 3d m → ns 13d m 4p 1 transitions, with n = 1, 2, 3 and m = 0, 1, 2, …, 10 involved in the s electron excitation process. Using the concept of ligand field, the Slater-Condon integrals, the spin-orbit coupling constants, and the parameters of the ligand field potential are determined from density functional theory (DFT). Therefore, a theoretical procedure using LFDFT is established illustrating the spectroscopic details at the atomic scale that can be valuable in the analysis and characterization of the electronic spectra obtained from X-ray absorption fine structure or electron energy loss spectroscopies.
DEFF Research Database (Denmark)
Mangiarotti, Alessio; Sona, Pietro; Ballestrero, Sergio
2012-01-01
Approximate analytical calculations of multi-photon effects in the spectrum of total radiated energy by high-energy electrons crossing thin targets are compared to the results of Monte Carlo type simulations. The limits of validity of the analytical expressions found in the literature are establi...
van Setten, Michiel J.; de Wijs, Gilles A.; Brocks, G.
2008-01-01
Alanates and boranates are intensively studied because of their potential use as hydrogen storage materials. In this paper, we present a first-principles study of the electronic structure and the energetics of beryllium boranate BeBH42. From total energy calculations, we show that—in contrast to the
Energy Technology Data Exchange (ETDEWEB)
Tohme, Samir N.; Korek, Mahmoud, E-mail: mahmoud.korek@bau.edu.lb, E-mail: fkorek@yahoo.com; Awad, Ramadan [Faculty of Science, Beirut Arab University, P.O. Box 11-5020 Riad El Solh, Beirut 1107 2809 (Lebanon)
2015-03-21
Ab initio techniques have been applied to investigate the electronic structure of the LiYb molecule. The potential energy curves have been computed in the Born–Oppenheimer approximation for the ground and 29 low-lying doublet and quartet excited electronic states. Complete active space self-consistent field, multi-reference configuration interaction, and Rayleigh Schrödinger perturbation theory to second order calculations have been utilized to investigate these states. The spectroscopic constants, ω{sub e}, R{sub e}, B{sub e}, …, and the static dipole moment, μ, have been investigated by using the two different techniques of calculation with five different types of basis. The eigenvalues, E{sub v}, the rotational constant, B{sub v}, the centrifugal distortion constant, D{sub v}, and the abscissas of the turning points, R{sub min} and R{sub max}, have been calculated by using the canonical functions approach. The comparison between the values of the present work, calculated by different techniques, and those available in the literature for several electronic states shows a very good agreement. Twenty-one new electronic states have been studied here for the first time.
Khaikin, L. S.; Tikhonov, D. S.; Grikina, O. E.; Rykov, A. N.; Stepanov, N. F.
2014-05-01
The equilibrium molecular structure of 2-methyl-1,4-naphthoquinone (vitamin K3) having C s symmetry is experimentally characterized for the first time by means of gas-phase electron diffraction using quantum-chemical calculations and data on the vibrational spectra of related compounds.
Energy Technology Data Exchange (ETDEWEB)
Mangiarotti, A. [Laboratorio de Instrumentacao e Fisica Experimental de Particulas, Coimbra (Portugal); Departamento de Fisica, Faculdade de Ciencias e Tecnologia da Universidade de Coimbra, Coimbra (Portugal); Sona, P., E-mail: pietro.sona@fi.infn.it [Dipartimento di Fisica e Astronomia, Universita degli Studi di Firenze, Polo Scientifico, Via G. Sansone 1, 50019 Sesto Fiorentino (Italy); INFN, Sezione di Firenze (Italy); Ballestrero, S. [Department of Physics University of Johannesburg, Johannesburg (South Africa); CERN PH/ADT, Geneve (Switzerland); Uggerhoj, U.I.; Andersen, K.K. [Department of Physics and Astronomy, University of Aarhus, Aarhus (Denmark)
2012-10-15
Approximate analytical calculations of multi-photon effects in the spectrum of total radiated energy by high-energy electrons crossing thin targets are compared to the results of Monte Carlo type simulations. The limits of validity of the analytical expressions found in the literature are established. The separate contributions to spectral distortion of electromagnetic processes other than bremsstrahlung are also studied in detail.
Epée Epée, M. D.; Motapon, O.; Darby-Lewis, D.; Tennyson, J.
2017-06-01
The UK molecular R-matrix codes are used to study electron collisions with the {{He}}2+ molecular ion. Full configuration interaction calculations are performed to obtain the potential energy curves of the ground X {}2{{{Σ }}}u+ and the first excited A {}2{{{Σ }}}g+ electronic states of {{He}}2+. Resonances, effective quantum numbers, and resonance widths as a function of the internuclear separation are determined for the lowest singlet {}1{{{Σ }}}g+,{}1{{{Σ }}}u+,{}1{{{\\Pi }}}g and {}1{{{\\Pi }}}u and triplet {}3{{{Σ }}}g+,{}3{{{Σ }}}u+,{}3{{{\\Pi }}}g,{}3{{{\\Pi }}}u and {}3{{{Δ }}}u states, which are relevant for the study of the reactive collision of {{He}}2+ with low-energy electrons. In addition, bound states are also calculated for each symmetry of {{He}}2 at several geometries.
Influence of the substitution on the electronic properties of perylene ...
African Journals Online (AJOL)
dicarboximides): density functional theory study. ... Taking into account the calculated electron affinities (EA), the air stability and ambipolar behavior of the materials under study can be expected. KEY WORDS: Organic field effect transistors, ...
Directory of Open Access Journals (Sweden)
Hirokazu Takaki
2014-01-01
Full Text Available We present an efficient computation technique for ab-initio electron transport calculations based on density functional theory and the nonequilibrium Green’s function formalism for application to heterostructures with two-dimensional (2D interfaces. The computational load for constructing the Green’s functions, which depends not only on the energy but also on the 2D Bloch wave vector along the interfaces and is thus catastrophically heavy, is circumvented by parallel computational techniques with the message passing interface, which divides the calculations of the Green’s functions with respect to energy and wave vectors. To demonstrate the computational efficiency of the present code, we perform ab-initio electron transport calculations of Al(100-Si(100-Al(100 heterostructures, one of the most typical metal-semiconductor-metal systems, and show their transmission spectra, density of states (DOSs, and dependence on the thickness of the Si layers.
Energy Technology Data Exchange (ETDEWEB)
Schweinler, H.C.; Christophorou, L.G.
1980-01-01
This model for the mononegative atomic or molecular ion in its effect on the most loosely bound electron is a spherical square well (constant positive inner potential within a sphere of radius r/sub 0/ and zero potential outside). From it we have calculated by quantum mechanics the emission rate w/sub ..nu..lm/ of electrons from the ..nu../sup th/ excited state (of orbital angular momentum and magnetic quantum numbers l and m and energy E/sub ..nu..l/ < 0) under the influence of a constant electric field F. The calculation is conceptionally simple (involving time-dependent perturbation theory) but technically complicated (requiring an eleven-fold integration), and leads to a surprisingly simple final expression. The relevance of our calculations to gaseous dielectrics is discussed.
Energy Technology Data Exchange (ETDEWEB)
Gibbons, John P., E-mail: john.gibbons@marybird.com [Department of Physics, Mary Bird Perkins Cancer Center, Baton Rouge, Louisiana 70809 (United States); Antolak, John A. [Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota 55905 (United States); Followill, David S. [Department of Radiation Physics, UT M.D. Anderson Cancer Center, Houston, Texas 77030 (United States); Huq, M. Saiful [Department of Radiation Oncology, University of Pittsburgh Cancer Institute, Pittsburgh, Pennsylvania 15232 (United States); Klein, Eric E. [Department of Radiation Oncology, Washington University School of Medicine, St. Louis, Missouri 63110 (United States); Lam, Kwok L. [Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109 (United States); Palta, Jatinder R. [Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298 (United States); Roback, Donald M. [Department of Radiation Oncology, Cancer Centers of North Carolina, Raleigh, North Carolina 27607 (United States); Reid, Mark [Department of Medical Physics, Fletcher-Allen Health Care, Burlington, Vermont 05401 (United States); Khan, Faiz M. [Department of Radiation Oncology, University of Minnesota, Minneapolis, Minnesota 55455 (United States)
2014-03-15
A protocol is presented for the calculation of monitor units (MU) for photon and electron beams, delivered with and without beam modifiers, for constant source-surface distance (SSD) and source-axis distance (SAD) setups. This protocol was written by Task Group 71 of the Therapy Physics Committee of the American Association of Physicists in Medicine (AAPM) and has been formally approved by the AAPM for clinical use. The protocol defines the nomenclature for the dosimetric quantities used in these calculations, along with instructions for their determination and measurement. Calculations are made using the dose per MU under normalization conditions, D{sub 0}{sup ′}, that is determined for each user's photon and electron beams. For electron beams, the depth of normalization is taken to be the depth of maximum dose along the central axis for the same field incident on a water phantom at the same SSD, where D{sub 0}{sup ′} = 1 cGy/MU. For photon beams, this task group recommends that a normalization depth of 10 cm be selected, where an energy-dependent D{sub 0}{sup ′} ≤ 1 cGy/MU is required. This recommendation differs from the more common approach of a normalization depth of d{sub m}, with D{sub 0}{sup ′} = 1 cGy/MU, although both systems are acceptable within the current protocol. For photon beams, the formalism includes the use of blocked fields, physical or dynamic wedges, and (static) multileaf collimation. No formalism is provided for intensity modulated radiation therapy calculations, although some general considerations and a review of current calculation techniques are included. For electron beams, the formalism provides for calculations at the standard and extended SSDs using either an effective SSD or an air-gap correction factor. Example tables and problems are included to illustrate the basic concepts within the presented formalism.
Gibbons, John P; Antolak, John A; Followill, David S; Huq, M Saiful; Klein, Eric E; Lam, Kwok L; Palta, Jatinder R; Roback, Donald M; Reid, Mark; Khan, Faiz M
2014-03-01
A protocol is presented for the calculation of monitor units (MU) for photon and electron beams, delivered with and without beam modifiers, for constant source-surface distance (SSD) and source-axis distance (SAD) setups. This protocol was written by Task Group 71 of the Therapy Physics Committee of the American Association of Physicists in Medicine (AAPM) and has been formally approved by the AAPM for clinical use. The protocol defines the nomenclature for the dosimetric quantities used in these calculations, along with instructions for their determination and measurement. Calculations are made using the dose per MU under normalization conditions, D'0, that is determined for each user's photon and electron beams. For electron beams, the depth of normalization is taken to be the depth of maximum dose along the central axis for the same field incident on a water phantom at the same SSD, where D'0 = 1 cGy/MU. For photon beams, this task group recommends that a normalization depth of 10 cm be selected, where an energy-dependent D'0 ≤ 1 cGy/MU is required. This recommendation differs from the more common approach of a normalization depth of dm, with D'0 = 1 cGy/MU, although both systems are acceptable within the current protocol. For photon beams, the formalism includes the use of blocked fields, physical or dynamic wedges, and (static) multileaf collimation. No formalism is provided for intensity modulated radiation therapy calculations, although some general considerations and a review of current calculation techniques are included. For electron beams, the formalism provides for calculations at the standard and extended SSDs using either an effective SSD or an air-gap correction factor. Example tables and problems are included to illustrate the basic concepts within the presented formalism.
Perturbation Calculation of two-electron interaction in the ground of ...
African Journals Online (AJOL)
The single-band Hubbard model was studied in one dimensional lattice system which consist only of two sites. The perturbation calculation accounts for the ground state energy and its wave functions .The exact and perturbation calculation are in agreement when the value of the on-site coulomb interaction U is equal to ...
An OpenCL-based Monte Carlo dose calculation engine (oclMC) for coupled photon-electron transport
Tian, Zhen; Folkerts, Michael; Qin, Nan; Jiang, Steve B; Jia, Xun
2015-01-01
Monte Carlo (MC) method has been recognized the most accurate dose calculation method for radiotherapy. However, its extremely long computation time impedes clinical applications. Recently, a lot of efforts have been made to realize fast MC dose calculation on GPUs. Nonetheless, most of the GPU-based MC dose engines were developed in NVidia CUDA environment. This limits the code portability to other platforms, hindering the introduction of GPU-based MC simulations to clinical practice. The objective of this paper is to develop a fast cross-platform MC dose engine oclMC using OpenCL environment for external beam photon and electron radiotherapy in MeV energy range. Coupled photon-electron MC simulation was implemented with analogue simulations for photon transports and a Class II condensed history scheme for electron transports. To test the accuracy and efficiency of our dose engine oclMC, we compared dose calculation results of oclMC and gDPM, our previously developed GPU-based MC code, for a 15 MeV electron ...
Shielding calculations for industrial 5/7.5MeV electron accelerators using the MCNP Monte Carlo Code
Peri, Eyal; Orion, Itzhak
2017-09-01
High energy X-rays from accelerators are used to irradiate food ingredients to prevent growth and development of unwanted biological organisms in food, and by that extend the shelf life of the products. The production of X-rays is done by accelerating 5 MeV electrons and bombarding them into a heavy target (high Z). Since 2004, the FDA has approved using 7.5 MeV energy, providing higher production rates with lower treatments costs. In this study we calculated all the essential data needed for a straightforward concrete shielding design of typical food accelerator rooms. The following evaluation is done using the MCNP Monte Carlo code system: (1) Angular dependence (0-180°) of photon dose rate for 5 MeV and 7.5 MeV electron beams bombarding iron, aluminum, gold, tantalum, and tungsten targets. (2) Angular dependence (0-180°) spectral distribution simulations of bremsstrahlung for gold, tantalum, and tungsten bombarded by 5 MeV and 7.5 MeV electron beams. (3) Concrete attenuation calculations in several photon emission angles for the 5 MeV and 7.5 MeV electron beams bombarding a tantalum target. Based on the simulation, we calculated the expected increase in dose rate for facilities intending to increase the energy from 5 MeV to 7.5 MeV, and the concrete width needed to be added in order to keep the existing dose rate unchanged.
Directory of Open Access Journals (Sweden)
Yaxuan Cai
2017-06-01
Full Text Available The electronic structure and ferroelectric mechanism of trichloroacetamide were studied using first principles calculations and density functional theory within the generalized gradient approximation. Using both Bader charge and electron deformation density, large molecular spontaneous polarization is found to originate from the charge transfer cause by the strong “push-pull” effect of electron-releasing interacting with electron-withdrawing groups. The intermolecular hydrogen bonds, NH⋯O, produce dipole moments in adjacent molecules to be aligned with each other. They also reduce the potential energy of the molecular chain threaded by hydrogen bonds. Due to the symmetric crystalline properties, however, the polarization of trichloroacetamide is mostly compensated and therefore small. Using the Berry Phase method, the spontaneous polarization of trichloroacetamide was simulated, and good agreement with the experimental values was found. Considering the polarization characteristics of trichloroacetamide, we constructed a one-dimensional ferroelectric Hamiltonian model to calculate the ferroelectric properties of TCAA. Using the Hamiltonian model, the thermal properties and ferroelectricity of trichloroacetamide were studied using the Monte Carlo method, and the Tc value was calculated.
Blancafort, Lluís; Voityuk, Alexander A
2017-11-20
The rate of photoinduced ET in molecular systems is controlled by electronic coupling of the locally excited and charge transfer states. We generalize the Bixon-Jortner-Verhoeven expression for electronic coupling to systems with a small energy gap and derive the transfer integral for charge separation in two model heterojunctions using the excitation energies and oscillator strengths computed with TD DFT. The estimated couplings are in good agreement with the reference values.
Electronic and optical properties of 2D graphene-like ZnS: DFT calculations
Energy Technology Data Exchange (ETDEWEB)
Lashgari, Hamed [Department of Physics, Science and Research Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of); Boochani, Arash, E-mail: arash_bch@yahoo.com [Department of Physics, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Shekaari, Ashkan [Department of Physics, Science and Research Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of); Solaymani, Shahram [Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Sartipi, Elmira [Department of Physics, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Mendi, Rohollah Taghavi [Department of Physics, Mashhad Branch, Islamic Azad University, Mashhad (Iran, Islamic Republic of)
2016-04-30
Graphical abstract: - Highlights: • DFT has been applied to investigate the optical properties of 2D-ZnS and 3D-ZnS. • The electronic and the optical properties of 3D-ZnS and 2D-ZnS are compared. • At visible range of energies the transparency of 2D-ZnS is more than the 3D. - Abstract: Density-functional theory has been applied to investigate the electronic and optical properties of graphene-like two-dimensional ZnS in the (0001) direction of its Wurtzite phase. A comparison with 3D-ZnS has been carried out within the PBE- and EV-GGA. The electronic properties of 2D- and 3D-ZnS have been derived by the examination of the electronic band structures and density of states. The optical properties have been determined through the study of the dielectric function, reflectivity, electron loss function, refractive and extinction indices, the absorption index and optical conductivity. It is found that the transparency of 2D-ZnS is greater than the 3D over the visible range. A thorough study of the dielectric function has been performed so that the peaks and the transition bands have been specified. The electron loss function demonstrates that the plasmonic frequency for 2D- and 3D-ZnS is accrued at 11.22 and 19.93 eV within the PBE-GGA, respectively.
Ocola, Esther J; Shin, Hee Won; Laane, Jaan
2015-02-05
The infrared and Raman spectra of vapor-phase and liquid-phase benzocyclobutane (BCB) have been recorded and assigned. The structure of the molecule was calculated using the MP2/cc-pVTZ basis set and the vibrational frequencies and spectral intensities were calculated using the B3LYP/cc-pVTZ level of theory. The agreement between experimental and calculated spectra is excellent. In order to allow comparisons with related molecules, ab initio and DFT calculations were also carried out for indan (IND), tetralin (TET), 1,4-benzodioxan (14BZD), 1,3-benzodioxan (13BZD) and 1,4-dihydronaphthalene (14DHN). The ring-puckering, ring-twisting, and ring-flapping vibrations were of particular interest as these reflect the rigidity of the bicyclic ring system. The infrared spectra of BCB show very nice examples of vapor-phase band types and combination bands. Copyright © 2014 Elsevier B.V. All rights reserved.
Ocola, Esther J.; Shin, Hee Won; Laane, Jaan
2015-02-01
The infrared and Raman spectra of vapor-phase and liquid-phase benzocyclobutane (BCB) have been recorded and assigned. The structure of the molecule was calculated using the MP2/cc-pVTZ basis set and the vibrational frequencies and spectral intensities were calculated using the B3LYP/cc-pVTZ level of theory. The agreement between experimental and calculated spectra is excellent. In order to allow comparisons with related molecules, ab initio and DFT calculations were also carried out for indan (IND), tetralin (TET), 1,4-benzodioxan (14BZD), 1,3-benzodioxan (13BZD) and 1,4-dihydronaphthalene (14DHN). The ring-puckering, ring-twisting, and ring-flapping vibrations were of particular interest as these reflect the rigidity of the bicyclic ring system. The infrared spectra of BCB show very nice examples of vapor-phase band types and combination bands.
Umari, P; Petrenko, O; Taioli, S; De Souza, M M
2012-05-14
Electronic band gaps for optically allowed transitions are calculated for a series of semiconducting single-walled zig-zag carbon nanotubes of increasing diameter within the many-body perturbation theory GW method. The dependence of the evaluated gaps with respect to tube diameters is then compared with those found from previous experimental data for optical gaps combined with theoretical estimations of exciton binding energies. We find that our GW gaps confirm the behavior inferred from experiment. The relationship between the electronic gap and the diameter extrapolated from the GW values is also in excellent agreement with a direct measurement recently performed through scanning tunneling spectroscopy.
Energy Technology Data Exchange (ETDEWEB)
Lewis, J.P.; Sewell, T.D.; Evans, R.B.; Voth, G.A.
2000-02-10
The molecular structures and energetic stabilities of the three pure polymorphic forms of crystalline HMX were calculated using a first-principles electronic-structure method. The computations were performed using the local density approximation in conjunction with localized fireball orbitals and a minimal basis set. Optimized cell parameters and molecular geometries were obtained, subject only to preservation of the experimental lattice angles and relative lattice lengths. The latter constraint was removed in some calculations for {beta}-HMX. Within these constraints, the comparison between theory and experiment is found to be good. The structures, relative energies of the polymorphs, and bulk moduli are in general agreement with the available experimental data.
Gyrokinetic calculations of steady-state particle transport in electron internal transport barriers
Energy Technology Data Exchange (ETDEWEB)
Fable, E; Sauter, O [Centre de Recherches en Physique des Plasmas, Association EURATOM-Confederation Suisse, Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland); Angioni, C [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, 85748 Garching (Germany)], E-mail: emiliano.fable@epfl.ch
2008-11-15
The appearance of an internal particle transport barrier, correlated with a heat transport barrier, during strongly electron heated discharges in reversed magnetic shear scenario is well-established experimental evidence. Turbulent transport is believed to be responsible for the observed inward pinch. The mechanisms for the sustainment of such peaked density profiles in the absence of core particle sources are analysed in the framework of collisionless linear gyrokinetic turbulence theory. In particular, it is elucidated how the thermodiffusive pinch can become the dominant contribution to the total inward pinch. In stationary conditions, the pinch is shown to be carried mostly by trapped electrons, while passing electrons give a smaller contribution. The pinch is maximized when two different microinstabilities, namely the ion temperature gradient mode and the trapped electron mode are believed to coexist at similar linear growth rates. To reach this state at high values of the normalized density gradient, it is necessary to reduce the trapped electron mode activity via different stabilizing mechanisms. The role of impurities is also briefly discussed. A comprehensive analytical-numerical study of the linear stability properties of the modes allows the understanding of the physical mechanism in detail and the clarification of the possible drive of the observed pinch.
Kong, Bo; Zhang, Yachao
2016-07-01
The electronic structures of the cubic GdH3 are extensively investigated using the ab initio many-body GW calculations treating the Gd 4f electrons either in the core (4f-core) or in the valence states (4f-val). Different degrees of quasiparticle (QP) self-consistent calculations with the different starting points are used to correct the failures of the GGA/GGA + U/HSE03 calculations. In the 4f-core case, GGA + G0W0 calculations give a fundamental band gap of 1.72 eV, while GGA+ GW0 or GGA + GW calculations present a larger band gap. In the 4f-val case, the nonlocal exchange-correlation (xc) functional HSE03 can account much better for the strong localization of the 4f states than the semilocal or Hubbard U corrected xc functional in the Kohn-Sham equation. We show that the fundamental gap of the antiferromagnetic (AFM) or ferromagnetic (FM) GdH3 can be opened up by solving the QP equation with improved starting point of eigenvalues and wave functions given by HSE03. The HSE03 + G0W0 calculations present a fundamental band gap of 2.73 eV in the AFM configuration, and the results of the corresponding GW0 and GW calculations are 2.89 and 3.03 eV, respectively. In general, for the cubic structure, the fundamental gap from G0W0 calculations in the 4f-core case is the closest to the real result. By G0W0 calculations in the 4f-core case, we find that H or Gd defects can strongly affect the band structure, especially the H defects. We explain the mechanism in terms of the possible electron correlation on the hydrogen site. Under compression, the insulator-to-metal transition in the cubic GdH3 occurs around 40 GPa, which might be a satisfied prediction.
Calculating the X-Ray Fluorescence from the Planet Mercury Due to High-Energy Electrons
Burbine, T. H.; Trombka, J. I.; Bergstrom, P. M., Jr.; Christon, S. P.
2005-01-01
The least-studied terrestrial planet is Mercury due to its proximity to the Sun, which makes telescopic observations and spacecraft encounters difficult. Our lack of knowledge about Mercury should change in the near future due to the recent launching of MESSENGER, a Mercury orbiter. Another mission (BepiColombo) is currently being planned. The x-ray spectrometer on MESSENGER (and planned for BepiColombo) can characterize the elemental composition of a planetary surface by measuring emitted fluorescent x-rays. If electrons are ejected from an atom s inner shell by interaction with energetic particles such as photons, electrons, or ions, electrons from an outer shell can transfer to the inner shell. Characteristic x-rays are then emitted with energies that are the difference between the binding energy of the ion in its excited state and that of the ion in its ground state. Because each element has a unique set of energy levels, each element emits x-rays at a unique set of energies. Electrons and ions usually do not have the needed flux at high energies to cause significant x-ray fluorescence on most planetary bodies. This is not the case for Mercury where high-energy particles were detected during the Mariner 10 flybys. Mercury has an intrinsic magnetic field that deflects the solar wind, resulting in a bow shock in the solar wind and a magnetospheric cavity. Electrons and ions accelerated in the magnetosphere tend to follow its magnetic field lines and can impact the surface on Mercury s dark side Modeling has been done to determine if x-ray fluorescence resulting from the impact of high-energy electrons accelerated in Mercury's magnetosphere can be detected by MESSENGER. Our goal is to understand how much bulk chemical information can be obtained from x-ray fluorescence measurements on the dark side of Mercury.
Energy Technology Data Exchange (ETDEWEB)
Song, T., E-mail: songting_lzjtu@yeah.net [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); School of Material Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 (China); Ma, Q. [School of Material Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 (China); Sun, X.W., E-mail: xsun@carnegiescience.edu [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015 (United States); Liu, Z.J., E-mail: liuzj_lzcu@163.com [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Department of Physics, Lanzhou City University, Lanzhou 730070 (China); Fu, Z.J. [School of Electrical and Electronic Engineering, Chongqing University of Arts and Sciences, Chongqing 402160 (China); Wei, X.P.; Wang, T.; Tian, J.H. [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China)
2016-09-07
The phase transition, electronic band structure, and equation of state (EOS) of cubic TcN are investigated by first-principles pseudopotential method based on density-functional theory. The calculated enthalpies show that TcN has a transformation between zincblende and rocksalt phases and the pressure determined by the relative enthalpy is 32 GPa. The calculated band structure indicates the metallic feature and it might make cubic TcN a better candidate for hard materials. Particular attention is paid to the predictions of volume, bulk modulus and its pressure derivative which play a central role in the formulation of approximate EOSs using the quasi-harmonic Debye model. - Highlights: • The phase transition pressure and electronic band structure for cubic TcN are determined. • Particular attention is paid to investigate the equation of state parameters for cubic TcN. • The thermodynamic properties up to 80 GPa and 3000 K are successfully predicted.
Coccia, Emanuele; Assaraf, Roland; Luppi, Eleonora; Toulouse, Julien
2017-07-01
We propose a method for obtaining effective lifetimes of scattering electronic states for avoiding the artificial confinement of the wave function due to the use of incomplete basis sets in time-dependent electronic-structure calculations of atoms and molecules. In this method, using a fitting procedure, the lifetimes are extracted from the spatial asymptotic decay of the approximate scattering wave functions obtained with a given basis set. The method is based on a rigorous analysis of the complex-energy solutions of the Schrödinger equation. It gives lifetimes adapted to any given basis set without using any empirical parameters. The method can be considered as an ab initio version of the heuristic lifetime model of Klinkusch et al. [J. Chem. Phys. 131, 114304 (2009)]. The method is validated on H and He atoms using Gaussian-type basis sets for the calculation of high-harmonic-generation spectra.
Energy Technology Data Exchange (ETDEWEB)
Baguena, A.; Shaw, M.; Williart, A. [Universidad Nacional de Educacion a Distancia, Dpto. Fisica de los Materiales, Madrid (Spain); Baguena, A. [Consejo de Seguridad Nuclear, Madrid (Spain); Garcia, G. [Instituto de Matematicas y Fisica Fundamental, Consejo Superior de Investigaciones Cientificas, Madrid (Spain)
2006-07-01
We describe the calculations and preliminary measures made for the installation of a X-ray generator tube. This device is going to be used for the secondary electron production from photonic primary radiation of up to 125 keV. With this experimental system, we will study the energetic and space distribution of produced secondary electrons by obtaining its spectrum of energies and its angular distribution. This method of measurement is going to be applied in different targets of radiological, environmental and biological interest. Calculations in the present article include: theoretical yield of X-rays production of the designed equipment, necessary shielding for the radiological safety of the installation staff, and an estimated dose due to their use. Characteristics of the installation and the equipment are described with this purpose. (author)
Calculated and experimental low-loss electron energy loss spectra of dislocations in diamond and GaN
Jones, R; Gutiérrez-Sosa, A; Bangert, U; Heggie, M I; Blumenau, A T; Frauenheim, T; Briddon, P R
2002-01-01
First-principles calculations of electron energy loss (EEL) spectra for bulk GaN and diamond are compared with experimental spectra acquired with a scanning tunnelling electron microscope offering ultra-high-energy resolution in low-loss energy spectroscopy. The theoretical bulk low-loss EEL spectra, in the E sub g to 10 eV range, are in good agreement with experimental data. Spatially resolved spectra from dislocated regions in both materials are distinct from bulk spectra. The main effects are, however, confined to energy losses lying above the band edge. The calculated spectra for low-energy dislocations in diamond are consistent with the experimental observations, but difficulties remain in understanding the spectra of threading dislocations in GaN.
Energy Technology Data Exchange (ETDEWEB)
Liu Qijun, E-mail: dianerliu@yahoo.com.c [State Key Lab of Solidification Processing, College of Materials Science and Engineering, Northwestern Polytechnical University, Xi' an, Shaanxi 710072 (China); Liu Zhengtang; Feng Liping [State Key Lab of Solidification Processing, College of Materials Science and Engineering, Northwestern Polytechnical University, Xi' an, Shaanxi 710072 (China)
2010-04-15
Structural parameters, elastic, electronic, bonding and optical properties of delafossite CuAlO{sub 2} have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The ground-state properties obtained by minimizing the total energy are in favorable agreement with the previous work. We have derived the bulk, shear and Young's modulus, Poisson coefficient for delafossite CuAlO{sub 2}. We estimated the Debye temperature of CuAlO{sub 2} from the acoustic velocity. Electronic and chemical bonding properties have been studied throughout the calculation of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions for delafossite CuAlO{sub 2}, the dielectric function is calculated, which shows a significant optical anisotropy in the components of polarization directions (1 0 0) and (0 0 1).
Cox, Courtney E; Phifer, Jeremy R; Ferreira da Silva, Larissa; Gonçalves Nogueira, Gabriel; Ley, Ryan T; O'Loughlin, Elizabeth J; Pereira Barbosa, Ana Karolyne; Rygelski, Brett T; Paluch, Andrew S
2017-02-01
Solubility parameter based methods have long been a valuable tool for solvent formulation and selection. Of these methods, the MOdified Separation of Cohesive Energy Density (MOSCED) has recently been shown to correlate well the equilibrium solubility of multifunctional non-electrolyte solids. However, before it can be applied to a novel solute, a limited amount of reference solubility data is required to regress the necessary MOSCED parameters. Here we demonstrate for the solutes methylparaben, ethylparaben, propylparaben, butylparaben, lidocaine and ephedrine how conventional molecular simulation free energy calculations or electronic structure calculations in a continuum solvent, here the SMD or SM8 solvation model, can instead be used to generate the necessary reference data, resulting in a predictive flavor of MOSCED. Adopting the melting point temperature and enthalpy of fusion of these compounds from experiment, we are able to predict equilibrium solubilities. We find the method is able to well correlate the (mole fraction) equilibrium solubility in non-aqueous solvents over four orders of magnitude with good quantitative agreement.
Cox, Courtney E.; Phifer, Jeremy R.; Ferreira da Silva, Larissa; Gonçalves Nogueira, Gabriel; Ley, Ryan T.; O'Loughlin, Elizabeth J.; Pereira Barbosa, Ana Karolyne; Rygelski, Brett T.; Paluch, Andrew S.
2017-02-01
Solubility parameter based methods have long been a valuable tool for solvent formulation and selection. Of these methods, the MOdified Separation of Cohesive Energy Density (MOSCED) has recently been shown to correlate well the equilibrium solubility of multifunctional non-electrolyte solids. However, before it can be applied to a novel solute, a limited amount of reference solubility data is required to regress the necessary MOSCED parameters. Here we demonstrate for the solutes methylparaben, ethylparaben, propylparaben, butylparaben, lidocaine and ephedrine how conventional molecular simulation free energy calculations or electronic structure calculations in a continuum solvent, here the SMD or SM8 solvation model, can instead be used to generate the necessary reference data, resulting in a predictive flavor of MOSCED. Adopting the melting point temperature and enthalpy of fusion of these compounds from experiment, we are able to predict equilibrium solubilities. We find the method is able to well correlate the (mole fraction) equilibrium solubility in non-aqueous solvents over four orders of magnitude with good quantitative agreement.
Electronic states of Myricetin. UV-Vis polarization spectroscopy and quantum chemical calculations.
Vojta, Danijela; Karlsen, Eva Marie; Spanget-Larsen, Jens
2017-02-15
Myricetin (3,3',4',5,5',7'-hexahydroxyflavone) was investigated by linear dichroism spectroscopy on molecular samples partially aligned in stretched poly(vinyl alcohol) (PVA). At least five electronic transitions in the range 40,000-20,000cm(-1) were characterized with respect to their wavenumbers, relative intensities, and transition moment directions. The observed bands were assigned to electronic transitions predicted with TD-B3LYP/6-31+G(d,p). Copyright © 2016 Elsevier B.V. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Kawakami, Kazuki; Fujimoto, Takasi [Kyoto Univ., Graduate School of Engineering, Kyoto (Japan)
2001-10-01
We treat classically the n-, l- and m{sub r}-changing transitions and ionization. Excitation cross sections against the final state energy continue smoothly to the 'ionization cross sections'. The steady state populations determined by elastic collisions among the degenerate states in the same n level show higher populations in the m{sub 1}=0 states, suggesting positive polarizations of Lyman lines emitted from plasmas having directional electrons. For ionization, the two outgoing electrons have large relative angles, suggesting reduced three body recombination rates for these plasmas. (author)
Density-functional calculation of van der Waals forces for free-electron-like surfaces
DEFF Research Database (Denmark)
Hult, E.; Hyldgaard, P.; Rossmeisl, Jan
2001-01-01
A recently proposed general density functional for asymptotic van der Waals forces is used to calculate van der Waals coefficients and reference-plane positions for realistic low-indexed Al surfaces. Results are given for a number of atoms and molecules outside the surfaces, as well...... as for the interaction between the surfaces themselves. The densities and static image-plane positions that are needed as input in the van der Waals functional are calculated self-consistently within density-functional theory using the generalized-gradient approximation, pseudopotentials, and plane waves. This study...... shows that the van der Waals density functional is applicable to realistic surfaces. The need for physically correct surface models, especially for open surfaces, is also illustrated. Finally the parameters for the anisotropic interaction of O-2 with Al are calculated....
Calculation of thermodynamic, electronic, and optical properties of monoclinic Mg2NiH4
Energy Technology Data Exchange (ETDEWEB)
Myers, W.R.; Richardson, T.J.; Rubin, M.D.; Wang, L-W.
2001-10-01
Ab initio total-energy density functional theory is used to investigate the low temperature (LT) monoclinic form of Mg2NiH4. The calculated minimum energy geometry of LT Mg2NiH4 is close to that determined from neutron diffraction data, and the NiH4 complex is close to a regular tetrahedron. The enthalpies of the phase change to high temperature (HT) pseudo-cubic Mg2NiH4 and of hydrogen absorption by Mg2Ni are calculated and compared with experimental values. LT Mg2NiH4 is found to be a semiconductor with an indirect band gap of 1.4 eV. The optical dielectric function of LT Mg2NiH4 differs somewhat from that of the HT phase. A calculated thin film transmittance spectrum is consistent with an experimental spectrum.
Masuda, Y; Murai, S; Saito, H; Murakami, H; Itoh, T
1988-01-01
A device for measuring ambulatory activity in mice was developed. The device consisted of a plastic case, a bed plate, a step board (as a detector) and a calculator (as a recorder). A 2.2 cm width section was cut out from the middle of the case bottom in the direction of the minor axis and a step board, a width of 2 cm, was placed in the opening. A short bolt was screwed into one end of the step board and the head of the bolt was placed on the equal key of the calculator. The calculator counted the number of times the mouse stood on the step board. The validity of the device was demonstrated by measuring the effect of methamphetamine (1-4 mg/kg) on the ambulatory activity in mice.
Energy Technology Data Exchange (ETDEWEB)
Katsukura, Hirotaka; Miyata, Tomohiro; Tomita, Kota; Mizoguchi, Teruyasu, E-mail: teru@iis.u-tokyo.ac.jp
2017-07-15
The effect of the van der Waals (vdW) interaction on the simulation of the electron energy-loss near edge structure (ELNES) by a first-principles band-structure calculation is reported. The effect of the vdW interaction is considered by the Tkatchenko-Scheffler scheme, and the change of the spectrum profile and the energy shift are discussed. We perform calculations on systems in the solid, liquid and gaseous states. The transition energy shifts to lower energy by approximately 0.1 eV in the condensed (solid and liquid) systems by introducing the vdW effect into the calculation, whereas the energy shift in the gaseous models is negligible owing to the long intermolecular distance. We reveal that the vdW interaction exhibits a larger effect on the excited state than the ground state owing to the presence of an excited electron in the unoccupied band. Moreover, the vdW effect is found to depend on the local electron density and the molecular coordination. In addition, this study suggests that the detection of the vdW interactions exhibited within materials is possible by a very stable and high resolution observation. - Highlights: • Effect of van der Waals (vdW) interaction in ELNES calculation is investigated. • The vdW interaction influences more to the excited state owing to the presence of excited electron. • The vdW interaction makes spectral shift to lower energy side by 0.1–0.01 eV. • The vdW interaction is negligible in gaseous materials due to long intermolecular distance.
Energy Technology Data Exchange (ETDEWEB)
Ferreira da Silva, F.; Lange, E. [Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal); Limão-Vieira, P., E-mail: plimaovieira@fct.unl.pt, E-mail: michael.brunger@flinders.edu.au, E-mail: maplima@ifi.unicamp.br [Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal); School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001 (Australia); Jones, N. C.; Hoffmann, S. V. [ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade, DK-8000 Århus C (Denmark); Hubin-Franskin, M.-J.; Delwiche, J. [Départment de Chimie, Institut de Chimie-Bât. B6C, Université de Liège, B-4000 Liège 1 (Belgium); Brunger, M. J., E-mail: plimaovieira@fct.unl.pt, E-mail: michael.brunger@flinders.edu.au, E-mail: maplima@ifi.unicamp.br [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001 (Australia); Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia); and others
2015-10-14
The electronic spectroscopy of isolated furfural (2-furaldehyde) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 3.5–10.8 eV energy-range, with absolute cross section measurements derived. Electron energy loss spectra are also measured over a range of kinematical conditions. Those energy loss spectra are used to derive differential cross sections and in turn generalised oscillator strengths. These experiments are supported by ab initio calculations in order to assign the excited states of the neutral molecule. The good agreement between the theoretical results and the measurements allows us to provide the first quantitative assignment of the electronic state spectroscopy of furfural over an extended energy range.
First-principles calculation of the structure and electronic properties of Fe-substituted Bi2Ti2O7
Huang, Jin-Dou; Zhang, Zhenyi; Lin, Feng; Dong, Bin
2017-12-01
We performed first-principles calculations to investigate the formation energy, geometry structure, and electronic property of Fe-doped Bi2Ti2O7 systems with different Fe doping content. The calculated formation energies indicate that the substitutional configurations of Fe-doping Bi2Ti2O7 are easy to obtain under O-rich growth condition, but their thermodynamic stability decreases with the increase of Fe content. The calculated spin-resolved density of states and band structures indicate that the introduction of Fe into Bi2Ti2O7 brings high spin polarization. The spin-down impurity levels in Fe x Bi2‑x Ti2O7 and spin-up impurity levels in Fe x Bi2Ti2‑x O7 systems locate in the bottom of conduction band and narrow the band gap significantly, thus leading to the absorption of visible light. Interestingly, the impurity states in Fe x Bi2‑x Ti2O7 are the efficient separation center of photogenerated electron and hole, and less affected by Fe doping content, in comparison, the levels of impurity band in Fe x Bi2Ti2‑x O7 systems are largely effected by the Fe doping content, and high Fe doping content is the key factor to improve the separating rate of photogenerated electron and hole.
First-principle calculation of electrons charge density in the diamond ...
African Journals Online (AJOL)
. It has been found that in each crystal, the total electrons charge density along the [100] and [010] directions are equal, however, the charge densities at a given distance from the center of the cell along [001] and [100] directions are not exactly
Electron and Ion Conductivity Calculations using the Model of Lee and More
Energy Technology Data Exchange (ETDEWEB)
Hayes, John C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2016-09-30
The following notes describe the ARES implementation of the inverse of the electron conduction coefficient, using the model of Lee and More, Physics of Fluids 27, page 1273, 1984. An addendum describing the modifications for analogous ion conduction coeffiecient appears at the bottom.
Krylov subspace method for evaluating the self-energy matrices in electron transport calculations
DEFF Research Database (Denmark)
Sørensen, Hans Henrik Brandenborg; Hansen, Per Christian; Petersen, D. E.
2008-01-01
We present a Krylov subspace method for evaluating the self-energy matrices used in the Green's function formulation of electron transport in nanoscale devices. A procedure based on the Arnoldi method is employed to obtain solutions of the quadratic eigenvalue problem associated with the infinite...
A Detailed Derivation of Gaussian Orbital-Based Matrix Elements in Electron Structure Calculations
Petersson, T.; Hellsing, B.
2010-01-01
A detailed derivation of analytic solutions is presented for overlap, kinetic, nuclear attraction and electron repulsion integrals involving Cartesian Gaussian-type orbitals. It is demonstrated how s-type orbitals can be used to evaluate integrals with higher angular momentum via the properties of Hermite polynomials and differentiation with…
Is C-50 a superaromat? Evidence from electronic structure and ring current calculations
Matias, Ana Sanz; Havenith, Remco W. A.; Alcami, Manuel; Ceulemans, Arnout
2016-01-01
The fullerene-50 is a 'magic number' cage according to the 2(N + 1)(2) rule. For the three lowest isomers of C-50 with trigonal and pentagonal symmetries, we calculate the sphericity index, the spherical parentage of the occupied p-orbitals, and the current density in an applied magnetic field. The
Electron transport in a Pt-CO-Pt nanocontact: Density functional theory calculations
DEFF Research Database (Denmark)
Strange, Mikkel; Thygesen, Kristian Sommer; Jacobsen, Karsten Wedel
2006-01-01
We have performed first-principles calculations for the mechanic and electric properties of pure Pt nanocontacts and a Pt contact with a single CO molecule adsorbed. For the pure Pt contacts we see a clear difference between point contacts and short chains in good agreement with experiments. We...
Energy Technology Data Exchange (ETDEWEB)
David R. Farley
2010-08-19
A model has been developed to calculate the ground-state rotational populations of homonuclear diatomic molecules in kinetic gases, including the effects of electron-impact excitation, wall collisions, and gas feed rate. The equations are exact within the accuracy of the cross sections used and of the assumed equilibrating effect of wall collisions. It is found that the inflow of feed gas and equilibrating wall collisions can significantly affect the rotational distribution in competition with non-equilibrating electron-impact effects. The resulting steady-state rotational distributions are generally Boltzmann for N≥3, with a rotational temperature between the wall and feed gas temperatures. The N=0,1,2 rotational level populations depend sensitively on the relative rates of electron-impact excitation versus wall collision and gas feed rates.
Li, Sen; Zhang, Chao; Min, Fanfei; Dai, Xing; Pan, Chengling; Cheng, Wei
2017-12-01
First-principles calculations are performed to investigate the crystal and electronic structures of BiOF crystal and its oxygen vacancy BiO7/8F. By analyzing the energy band structures, the total density of states and the partial densities of states, it is found that the band gaps for the perfect BiOF and BiO7/8F are 3.12 and 2.65 eV, respectively, which are smaller than the experiment value of 3.64 eV. There is a new electronic state within the forbidden band in the BiO7/8F, which could serve as a capture center for excited electrons, consequently improves the effective separation of electron-hole pairs, and makes the optical absorption band edge red shift. The calculated results demonstrate that the BiOF crystal and its oxygen vacancy BiO7/8F could be the potential application as photocatalytic semiconductor materials.
Pan, Yong; Jin, Chao; Mao, Pengyu
2017-11-01
RuAl2 is a fascinating intermetallic semiconducting compound. However, the influence of vacancies on the electronic and mechanical properties of RuAl2 is unknown. By means of first-principles calculations, we have investigated the influence of vacancies on the electronic properties, elastic modulus, brittle or ductile behavior and Vickers hardness of RuAl2. Two possible vacancy types, Ru-va and Al-va, are considered. The calculated results show that the Ru-va vacancy is more thermodynamically stable than that of the Al-va vacancy. Importantly, we find that vacancies can improve the electronic properties of RuAl2 because the removed Ru or Al atom enhances the charge overlap between conduction band and the valence band near the Fermi level. In addition, these vacancies weaken the resistance to volume deformation, shear deformation and the elastic stiffness of RuAl2 because the removed atom weakens the localized hybridization between the Ru atom and the Al atom. However, the Ru-va vacancy can improve the Vickers hardness and Al-va vacancies result in brittle-to-ductile transition of RuAl2. The variation of mechanical properties is attributed to the Ru-Al and Al-Al metallic bonds along the shear direction. Therefore, we can conclude that vacances are beneficial for improving the electronic and mechanical properties of RuAl2.
Directory of Open Access Journals (Sweden)
M. I. Baranov
2016-12-01
Full Text Available Purpose. Development of calculation-experimental method for a discovery and study of electronic wavepackages (EWP and of de Broglie electronic half-waves in a metallic conductor with the pulse axial-flow current of high density. Methodology. Theoretical bases of the electrical engineering, bases of quantum physics, electrophysics bases of technique of high voltage and large pulsecurrents, and also bases of technique of measuring of permanent and variable electric value. Results. On the basis of generalization of results of research of features of the longitudinal wave periodic distributing of negatively charged transmitters of electric current of conductivity in the thin round continuous zincked steel wire offered and approved in the conditions of high-voltage laboratory method for a discovery and direct determination in him of geometrical parameters of «hot» and «cold» longitudinal areas quantized periodic longitudinal EWP and accordingly the mediated determination of values of the quantized lengths formative their de Broglie electronic half-waves. It is shown that results of close quantum mechanical calculations of EWP and quantized lengths λenz/2 of longitudinal de Broglie half-waves for the probed wire long l0 well comport with the results of the executed high temperature experiments on the powerful high-voltage generator of homopolar large pulse current of millisecond duration. Originality. First calculation-experimental a way the important for the theory of electricity fact of existence is set in a round metallic explorer with the impulsive axial-flow current of the quantized coherent de Broglie electronic half-waves, amplitudes of which at the quantum number of n=1,3,9 correspond the middles of «hot» longitudinal areas of EWP. Calculation quantum mechanical correlation of type of λenz/2=l0/n got experimental confirmation, in obedience to which on length of l0 conductor the integer of quantized electronic half-waves is always laid
DEFF Research Database (Denmark)
Bak, Keld L.; Hansen, Aage E.; Ruud, K.
1995-01-01
The second-quantization magnetic dipole operator that arises when London atomic orbitals are used as basis functions is derived. In atomic units, the magnetic dipole operator is defined as the negative of the first derivative of the electronic Hamiltonian containing the interaction with the exter......The second-quantization magnetic dipole operator that arises when London atomic orbitals are used as basis functions is derived. In atomic units, the magnetic dipole operator is defined as the negative of the first derivative of the electronic Hamiltonian containing the interaction...... that the length expression for the rotatory strength in linear response calculations gives gauge-origin-independent results. Sample calculations on ti ans-cyclooctene and its fragments are presented. Compared to conventional orbitals, the basis set convergence of the rotatory strengths calculated in the length...... form using London atomic orbitals is favourable. The rotatory strength calculated for trans-cyclooctene agrees nicely with the corresponding experimental circular dichroism spectrum, but the spectra for the fragment molecules show little resemblance with that of trans-cyclooctene....
Engel-Vosko GGA calculations of the structural, electronic and optical properties of LiYO2
Muhammad, Nisar; Khan, Afzal; Haidar Khan, Shah; Sajjaj Siraj, Muhammad; Shah, Syed Sarmad Ali; Murtaza, Ghulam
2017-09-01
Structural, electronic and optical properties of lithium yttrium oxide (LiYO2) are investigated using density functional theory (DFT). These calculations are based on full potential linearized augmented plane wave (FP-LAPW) method implemented by WIEN2k. The generalized gradient approximation (GGA) is used as an exchange correlation potential with Perdew-Burk-Ernzerhof (PBE) and Engel-Vosko (EV) as exchange correlation functional. The structural properties are calculated with PBE-GGA as it gives the equilibrium lattice constants very close to the experimental values. While, the band structure and optical properties are calculated with EV-GGA obtain much closer results to their experimental values. Our calculations confirm LiYO2 as large indirect band gap semiconductor having band gap of 5.23 eV exhibiting the characteristics of ultrawide band gap materials showing the properties like higher critical breakdown field, higher temperature operation and higher radiation tolerance. In this article, we report the density of states (DOS) in terms of contribution from s, p, and d-states of the constituent atoms, the band structure, the electronic structure, and the frequency-dependent optical properties of LiYO2. The optical properties presented in this article reveal LiYO2 a suitable candidate for the field of optoelectronic and optical devices.
Marochkin, Ilya I.; Altova, Ekaterina P.; Rykov, Anatolii N.; Shishkov, Igor F.
2017-11-01
The molecular structure of tryptamine was studied by gas-phase electron diffraction (GED) and quantum chemical calculations (DFT/B3LYP and MP2 methods with cc-pVTZ basis set). The best fit of the experimental scattering intensities (R-factor = 3.8%) was obtained for the four-conformer model. The experimental structural parameters are found to be in good agreement with the results of theoretical calculations. The geometric parameters of gaseous tryptamine are compared with those in the crystal phase. The standard enthalpy of formation of tryptamine in the gas phase was calculated using Gaussian-4 theory, yielding value of 133.6 ± 3.3 kJ/mol.
Fragment transition density method to calculate electronic coupling for excitation energy transfer
Energy Technology Data Exchange (ETDEWEB)
Voityuk, Alexander A., E-mail: alexander.voityuk@icrea.cat [Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain and Institut de Química Computacional i Catàlisi (IQCC), Universitat de Girona 17071 Girona (Spain)
2014-06-28
A general approach, the Fragment Transition Density (FTD) scheme, is introduced to estimate electronic coupling for excitation energy transfer in a molecular system. Within this method, the excitation energies and transition densities of the system are used to derive the coupling matrix element. The scheme allows one to treat systems where exciton donor and acceptor are close together and their exchange interaction and orbital overlap are significant. The FTD method can be applied in combination with any quantum mechanical approach to treat excited states of general nature including single-, double-, and higher excitations. Using FTD approach, we derive excitonic couplings for several systems computed with the CIS, TD DFT and MS-CASPT2 methods. In particular, it is shown that the estimated coupling values in DNA π-stacks are strongly affected by the short-range electronic interaction of adjacent nucleobases.
2015-11-18
Number: 88ABW-2015-1249; Clearance Date: 19 Mar 2015. This document contains color. Journal article published in the Journal of Applied Physics, Vol...JOURNAL OF APPLIED PHYSICS 118, 195302 (2015) [This article is copyrighted as indicated in the article . Reuse of AIP content is subject to the terms at...METHODS Calculations were performed using the Vienna ab initio simulation package VASP 5.3 (Refs. 42 and 43) within the framework of DFT. The projector
The electronic structure of LaO: Ligand field versus ab initio calculations
Schamps, Joël; Bencheikh, Mohammed; Barthelat, Jean-Claude; Field, Robert W.
1995-11-01
The potentially pathological example of LaO has been chosen to test the application of ligand field theory (LFT) to metal monoxides. The test consists of a comparison of closed-shell ligand LFT (CSLLFT) results (in which a 2+/2- ionic M2+O2- model is a priori postulated with a point-charge ligand) against ab initio multiconfiguration self-consistent-field-multireference configuration interaction (MCSCF-MRCI) results (in which no ionicity is assumed a priori and an internal structure is allowed for the ligand). Special care has been devoted to the determination of a La3+ pseudopotential and its associated atomic basis set in order to keep the ab initio model close to the LFT one, yet at the same time capable of clearly exhibiting the consequences and the importance of the restrictions imposed in the CSLLFT model. The ab initio calculations reveal that the effective (Mulliken) ionicity in LaO is not La2+O2- but quite close to La+O-. Despite this, the (2+/2-) ionic CSLLFT model leads to the correct orbital occupations in the ground state but this model cannot account for the significant covalency contribution via the nominal 2pσ and 2pπ oxygen orbitals. The CSLLFT calculations correctly reproduce the excitation energies of the four lowest-lying observed states of LaO: these states are calculated to within 2000 cm-1 and globally better than via ab initio calculations. However, the (2+/2-) ionic CSLLFT model is shown to ignore the existence of a manifold of low-lying quartet (and doublet) states of (1+/1-) ionicity that might be relevant for interpreting features of the spectrum. This result exemplifies the need for developing, beyond the first attempts made in this direction, a computationally manageable open-shell ligand theory for the frequently encountered case of predominantly ionic structures with an open-shell ligand.
Sparta, Manuel; Hansen, Mikkel B; Matito, Eduard; Toffoli, Daniele; Christiansen, Ove
2010-10-12
The availability of an accurate representation of the potential energy surface (PES) is an essential prerequisite in an anharmonic vibrational calculation. At the same time, the high dimensionality of the fully coupled PES and the adverse scaling properties with respect to the molecular size make the construction of an accurate PES a computationally demanding task. In the past few years, our group tested and developed a series of tools and techniques aimed at defining computationally efficient, black-box protocols for the construction of PESs for use in vibrational calculations. This includes the definition of an adaptive density-guided approach (ADGA) for the construction of PESs from an automatically generated set of evaluation points. Another separate aspect has been the exploration of the use of derivative information through modified Shepard (MS) interpolation/extrapolation procedures. With this article, we present an assembled machinery where these methods are embedded in an efficient way to provide both a general machinery as well as concrete computational protocols. In this framework we introduce and discuss the accuracy and computational efficiency of two methods, called ADGA[2gx3M] and ADGA[2hx3M], where the ADGA recipe is used (with MS interpolation) to automatically define modest sized grids for up to two-mode couplings, while MS extrapolation based on, respectively, gradients only and gradients and Hessians from the ADGA determined points provides access to sufficiently accurate three-mode couplings. The performance of the resulting potentials is investigated in vibrational coupled cluster (VCC) calculations. Three molecular systems serve as benchmarks: a trisubstituted methane (CHFClBr), methanimine (CH2NH), and oxazole (C3H3NO). Furthermore, methanimine and oxazole are addressed in accurate calculations aiming to reproduce experimental results.
Energy Technology Data Exchange (ETDEWEB)
Tucker, Jon R.; Magyar, Rudolph J.
2012-02-01
High explosives are an important class of energetic materials used in many weapons applications. Even with modern computers, the simulation of the dynamic chemical reactions and energy release is exceedingly challenging. While the scale of the detonation process may be macroscopic, the dynamic bond breaking responsible for the explosive release of energy is fundamentally quantum mechanical. Thus, any method that does not adequately describe bonding is destined to lack predictive capability on some level. Performing quantum mechanics calculations on systems with more than dozens of atoms is a gargantuan task, and severe approximation schemes must be employed in practical calculations. We have developed and tested a divide and conquer (DnC) scheme to obtain total energies, forces, and harmonic frequencies within semi-empirical quantum mechanics. The method is intended as an approximate but faster solution to the full problem and is possible due to the sparsity of the density matrix in many applications. The resulting total energy calculation scales linearly as the number of subsystems, and the method provides a path-forward to quantum mechanical simulations of millions of atoms.
Energy Technology Data Exchange (ETDEWEB)
Borges, A.; Solomon, G. C. [Department of Chemistry and Nano-Science Center, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø (Denmark)
2016-05-21
Single molecule conductance measurements are often interpreted through computational modeling, but the complexity of these calculations makes it difficult to directly link them to simpler concepts and models. Previous work has attempted to make this connection using maximally localized Wannier functions and symmetry adapted basis sets, but their use can be ambiguous and non-trivial. Starting from a Hamiltonian and overlap matrix written in a hydrogen-like basis set, we demonstrate a simple approach to obtain a new basis set that is chemically more intuitive and allows interpretation in terms of simple concepts and models. By diagonalizing the Hamiltonians corresponding to each atom in the molecule, we obtain a basis set that can be partitioned into pseudo-σ and −π and allows partitioning of the Landuaer-Büttiker transmission as well as create simple Hückel models that reproduce the key features of the full calculation. This method provides a link between complex calculations and simple concepts and models to provide intuition or extract parameters for more complex model systems.
Relativistic calculations of quasi-one-electron atoms and ions using Laguerre and Slater spinors
Jiang, Jun; Cheng, Yongjun; Bromley, Michael W J
2016-01-01
A relativistic description of the structure of heavy alkali atoms and alkali-like ions using S-spinors and L-spinors has been developed. The core wavefunction is defined by a Dirac-Fock calculation using an S-spinors basis. The S-spinor basis is then supplemented by a large set of L-spinors for the calculation of the valence wavefunction in a frozen-core model. The numerical stability of the L-spinor approach is demonstrated by computing the energies and decay rates of several low-lying hydrogen eigenstates, along with the polarizabilities of a $Z=60$ hydrogenic ion. The approach is then applied to calculate the dynamic polarizabilities of the $5s$, $4d$ and $5p$ states of Sr$^+$. The magic wavelengths at which the Stark shifts between different pairs of transitions are zero are computed. Determination of the magic wavelengths for the $5s \\to 4d_{\\frac32}$ and $5s \\to 4d_{\\frac52}$ transitions near $417$~nm (near the wavelength for the $5s \\to 5p_j$ transitions) would allow a determination of the oscillator s...
Directory of Open Access Journals (Sweden)
Steven J. Gortler
2013-12-01
Full Text Available We study the properties of affine rigidity of a hypergraph and prove a variety of fundamental results. First, we show that affine rigidity is a generic property (i.e., depends only on the hypergraph, not the particular embedding. Then we prove that a graph is generically neighborhood affinely rigid in d-dimensional space if it is (d+1-vertex-connected. We also show neighborhood affine rigidity of a graph implies universal rigidity of its squared graph. Our results, and affine rigidity more generally, have natural applications in point registration and localization, as well as connections to manifold learning.
Energy Technology Data Exchange (ETDEWEB)
Bannikov, V.V.; Ivanovskii, A.L., E-mail: ivanovskii@ihim.uran.ru
2013-11-15
Highlights: • 23 Pd- and Pt-based antiperovskite-type ternary carbides are probed from first principles. • Structural, elastic, electronic properties and inter-atomic bonding are evaluated. • A rich variety of mechanical and electronic properties was predicted. -- Abstract: By means of first-principles calculations, the structural, elastic, and electronic properties of a broad series of proposed Pd- and Pt-based antiperovskite-type ternary carbides AC(Pd,Pt){sub 3}, where A are Zn, Ca, Al, Ga, In, Ge, Hg, Sn, Cd, Pb, Ag, Sc, Ti, Y, Nb, Mo, and Ta, have been studied, and their stability, elastic constants, bulk, shear, and Young’s moduli, compressibility, Pugh’s indicator, Poisson’s ratio, indexes of elastic anisotropy, as well as electronic properties have been evaluated. We found that these materials should demonstrate a rich variety of mechanical and electronic properties depending on the type of A sublattices, which can include (unlike the majority of known 3d-metal-based antiperovskites) both sp elements and d atoms. We believe that the presented results will be useful for future synthesis of these phases, as well as for expanding our knowledge of this interesting group of antiperovskite-type materials.
Calculated Electronic Behavior and Spectrum of Mg+@C60 Using a Simple Jellium-shell Model
Directory of Open Access Journals (Sweden)
H. A. Schuessler
2004-11-01
Full Text Available Abstract: We present a method for calculating the energy levels and wave functions of any atom or ion with a single valence electron encapsulated in a Fullerene cage using a jelluim-shell model. The valence electron-core interaction is represented by a one-body pseudo-potential obtained through density functional theory with strikingly accurate parameters for Mg+ and which reduces to a purely Coulombic interaction in the case of H. We find that most energy states are affected little by encapsulation. However, when either the electron in the non-encapsulated species has a high probability of being near the jellium cage, or when the cage induces a maximum electron probability density within it, the energy levels shift considerably. Mg+ shows behavior similar to that of H, but since its wave functions are broader, the changes in its energy levels from encapsulation are slightly more pronounced. Agreement with other computational work as well as experiment is excellent and the method presented here is generalizable to any encapsulated species where a one-body electronic pseudo-potential for the free atom (or ion is available. Results are also presented for off-center hydrogen, where a ground state energy minimum of -14.01 eV is found at a nuclear displacement of around 0.1 ÃƒÂ….
Jette, D
1999-06-01
In modern photon dose-calculation algorithms one is frequently called upon to evaluate the integral at various points throughout the irradiated material of a dose or particle transport quantity multiplied by a weighting factor. For example, for a given dose-calculation point one might be integrating the product of the dose deposited by a monoenergetic beam and the energy distribution of the actual beam, and want to do this throughout the treatment volume. We have developed explicit formulas for replacing such integrations with a weighted sum of two or three functions (of, for example, the point of dose calculation) in order to greatly reduce the calculation time for the algorithm being used. We demonstrate the accuracy of this method of representing dose and particle transport integrals through comparisons with Monte Carlo calculations of dose distributions for two typical problems, in dealing with the energy spectrum of the photon beam and with the energy deposited by all the Compton electrons emerging from a particular interaction point, respectively.
Barghouty, A. F.
2014-01-01
Accurate estimates of electroncapture cross sections at energies relevant to the modeling of the transport, acceleration, and interaction of energetic neutral atoms (ENA) in space (approximately few MeV per nucleon) and especially for multi-electron ions must rely on detailed, but computationally expensive, quantum-mechanical description of the collision process. Kuang's semi-classical approach is an elegant and efficient way to arrive at these estimates. Motivated by ENA modeling efforts for apace applications, we shall briefly present this approach along with sample applications and report on current progress.
Chebodayev, M. I.
2017-10-01
Within the framework of the linear thermal elasticity theory a dynamic thermoelastic bending of a whisker crystal is considered under conditions of its irradiation with a high-current electron beam of nanosecond duration. It is shown that the characteristic time of leveling the temperature of superthin pin-type rod nonuniformely heated over its thickness is comparable with the period of the fundamental wave of flexural vibrations. This gives rise to a considerable decrease in the bending amplitude, which is concurrent with the heat conduction processes.
Fang, CM; vanSmaalen, S; Wiegers, GA; Haas, C; deGroot, RA
1996-01-01
In order to understand the electronic structure of the misfit layer compound (LaS)(1.14)NbS2 we carried out an ab initio band-structure calculation in a supercell approximation. The band structure is compared with that of the components NbS2 and LaS. The calculations show that the electronic
First-principles calculation of electronic energy level alignment at electrochemical interfaces
Energy Technology Data Exchange (ETDEWEB)
Azar, Yavar T.; Payami, Mahmoud, E-mail: mpayami@aeoi.org.ir
2017-08-01
Highlights: • Using DFT calculation, level shifts of TiO{sub 2} and ZnO at the interfaces with MeCN and DMF are determined. • Level shifts are obtained using potential difference between the surfaces of asymmetric slabs. • Solvent molecules give an up-shift to the levels that varies with coverage. • MD simulations show that at room temperatures the surface is not fully covered by the solvent molecules. - Abstract: Energy level alignment at solid–solvent interfaces is an important step in determining the properties of electrochemical systems. The positions of conduction and valence band edges of a semiconductor are affected by its environment. In this study, using first-principles DFT calculation, we have determined the level shifts of the semiconductors TiO{sub 2} and ZnO at the interfaces with MeCN and DMF solvent molecules. The level shifts of semiconductor are obtained using the potential difference between the clean and exposed surfaces of asymmetric slabs. In this work, neglecting the effects of present ions in the electrolyte solution, we have shown that the solvent molecules give rise to an up-shift for the levels, and the amount of this shift varies with coverage. It is also shown that the shapes of density of states do not change sensibly near the gap. Molecular dynamics simulations of the interface have shown that at room temperatures the semiconductor surface is not fully covered by the solvent molecules, and one must use intermediate values in an static calculations.
Energy Technology Data Exchange (ETDEWEB)
Carlsund, C. (Manne Siegbahn Inst. of Physics, Stockholm (Sweden) Dept. of Theoretical Physics, Royal Inst. of Tech., Stockholm (Sweden)); Krylstedt, P. (Manne Siegbahn Inst. of Physics, Stockholm (Sweden) Dept. of Theoretical Physics, Royal Inst. of Tech., Stockholm (Sweden) Swedish National Defence Establishment, Stockholm (Sweden)); Elander, N. (Manne Siegbahn Inst. of Physics, Stockholm (Sweden)); Cowan, R.D. (Los Alamos National Lab., NM (USA))
1990-09-01
Our work on analytically continued scattering theory based on the Schroedinger equation is reviewed. We give a brief description of how resonances, here defined as partial wave S-matrix poles, can be calculated as complex eigenvalues to the complex scaled Schroedinger equation. A Mittag-Leffler type expansion is then introduced and it is shown how one can partition a scattering cross section into contributions from isolated S-matrix poles and a background. Computationally this method has proven to be considerably faster than conventional methods. A new, faster and more accurate integration method is used. Examples of detailed previous work as well as current research are given. (orig.).
García-Risueño, Pablo; Alberdi-Rodriguez, Joseba; Oliveira, Micael J T; Andrade, Xavier; Pippig, Michael; Muguerza, Javier; Arruabarrena, Agustin; Rubio, Angel
2014-03-05
We present an analysis of different methods to calculate the classical electrostatic Hartree potential created by charge distributions. Our goal is to provide the reader with an estimation on the performance-in terms of both numerical complexity and accuracy-of popular Poisson solvers, and to give an intuitive idea on the way these solvers operate. Highly parallelizable routines have been implemented in a first-principle simulation code (Octopus) to be used in our tests, so that reliable conclusions about the capability of methods to tackle large systems in cluster computing can be obtained from our work. Copyright © 2013 Wiley Periodicals, Inc.
Beam line shielding calculations for an Electron Accelerator Mo-99 production facility
Energy Technology Data Exchange (ETDEWEB)
Mocko, Michal [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-05-03
The purpose of this study is to evaluate the photon and neutron fields in and around the latest beam line design for the Mo-99 production facility. The radiation dose to the beam line components (quadrupoles, dipoles, beam stops and the linear accelerator) are calculated in the present report. The beam line design assumes placement of two cameras: infra red (IR) and optical transition radiation (OTR) for continuous monitoring of the beam spot on target during irradiation. The cameras will be placed off the beam axis offset in vertical direction. We explored typical shielding arrangements for the cameras and report the resulting neutron and photon dose fields.
On the calculation of Δ for electronic excitations in time-dependent density-functional theory
Myneni, Hemanadhan; Casida, Mark E.
2017-04-01
Excited states are often treated within the context of time-dependent (TD) density-functional theory (DFT), making it important to be able to assign the excited spin-state symmetry. While there is universal agreement on how Δ , the difference between for ground and excited states, should be calculated in a wave-function-like formalism such as the Tamm-Dancoff approximation (TDA), confusion persists as to how to determine the spin-state symmetry of excited states in TD-DFT. We try to clarify the origins of this confusion by examining various possibilities for the parameters (σ1 ,σ2) in the formula
Strenalyuk, Tatyana; Samdal, Svein; Volden, Hans Vidar
2007-11-29
The molecular structures of phthalocyaninatozinc (HPc-Zn) and hexadecafluorophthalocyaninatozinc (FPc- Zn) are determined using the gas electron diffraction (GED) method and high-level density functional theory (DFT) quantum chemical calculations. Calculations at the B3LYP/6-311++G** level indicate that the equilibrium structures of HPc-Zn and FPc-Zn have D4h symmetry and yield structural parameters in good agreement with those obtained by GED at 480 and 523 degrees C respectively. The calculated force fields indicate that both molecules are flexible. Normal coordinate calculations on HPc-Zn yield five vibrational frequencies (one degenerate) in the range 22-100 cm(-1), and ten vibrational frequencies ranging from 13 to 100 cm(-1) (three degenerate) for FPc-Zn. The high-level force field calculations confirm most of the previous vibrational assignments, and some new ones are suggested. The out-of-plane vibration of the Zn atom in HPc-Zn was studied in detail optimizing models in which the distance from the Zn atom to the two symmetry equivalent diagonally opposed N atoms (h) was fixed. The calculations indicate that the vibrationally activated vertically displacement of the Zn atom is accompanied by distortion of the ligand from D4h to C2v symmetry. The average height, h, at the temperature of the GED experiment was calculated to be 14.5 pm. Small structural changes indicate that a full F substitution on the benzo-subunits do not significantly alter the geometry, however there are indications that the benzo-subunits may shrink slightly with perfluorination.
CO2 adsorption on Fe-doped graphene nanoribbons: First principles electronic transport calculations
Directory of Open Access Journals (Sweden)
G. R. Berdiyorov
2016-12-01
Full Text Available Decoration of graphene with metals and metal-oxides is known to be one of the effective methods to enhance gas sensing and catalytic properties of graphene. We use density functional theory in combination with the nonequilibrium Green’s function formalism to study the conductance response of Fe-doped graphene nanoribbons to CO2 gas adsorption. A single Fe atom is either adsorbed on graphene’s surface (aFe-graphene or it substitutes the carbon atom (sFe-graphene. Metal atom doping reduces the electronic transmission of pristine graphene due to the localization of electronic states near the impurities. The reduction in the transmission is more pronounced in the case of aFe-graphene. In addition, the aFe-graphene is found to be less sensitive to the CO2 molecule attachment as compared to the sFe-graphene system. Pristine graphene is also found to be less sensitive to the molecular adsorption. Since the change in the conductivity is one of the main outputs of sensors, our findings will be useful in developing graphene-based solid-state gas sensors.
Li, Yanli; Dabo, Ismaila
2011-10-01
Plane-wave electronic-structure predictions based upon orbital-dependent density-functional theory (OD-DFT) approximations, such as hybrid density-functional methods and self-interaction density-functional corrections, are severely affected by computational inaccuracies in evaluating electron interactions in the plane-wave representation. These errors arise from divergence singularities in the plane-wave summation of electrostatic and exchange interaction contributions. Auxiliary-function corrections are reciprocal-space countercharge corrections that cancel plane-wave singularities through the addition of an auxiliary function to the point-charge electrostatic kernel that enters into the expression of interaction terms. At variance with real-space countercharge corrections that are employed in the context of density-functional theory (DFT), reciprocal-space corrections are computationally inexpensive, making them suited to more demanding OD-DFT calculations. Nevertheless, there exists much freedom in the choice of auxiliary functions and various definitions result in different levels of performance in eliminating plane-wave inaccuracies. In this work we derive exact point-charge auxiliary functions for the description of molecular structures of arbitrary translational symmetry, including the yet unaddressed one-dimensional case. In addition, we provide a critical assessment of different reciprocal-space countercharge corrections and demonstrate the improved accuracy of point-charge auxiliary functions in predicting the electronic levels and electrical response of conjugated polymers from plane-wave OD-DFT calculations.
Calculation of the electron and hole impact ionization rate for wurtzite AlN and GaN
Li, G. R.; Qin, Z. X.; Luo, G. F.; Shen, B.; Zhang, G. Y.
2010-11-01
The interband impact ionization transition rate (IIR) of electrons and holes in wurtzite GaN and AlN is calculated using full local density approximation (LDA) band structures under the scissor approximation. The IIR of AlN is first calculated and the results show a large difference between the IIR of electrons and holes. The IIR of electrons grows from zero to 1014 at energies of ~6.6-10 eV, while the IIR of holes is zero below 12.2 eV. The difference is interpreted by the energy gap between the sixth and the seventh valence bands. Analysis shows that it is hard for holes in AlN to tunnel through the large energy gap between the sixth and the seventh valence bands; as a result, holes can hardly get enough energy for impact ionization in the electrical field of several MV cm-1. This indicates that AlN is a good material for avalanche photodetectors of controllable gain, low noise and wide bandwidth with a cutoff wavelength of 210 nm. To further facilitate Monte Carlo simulation, the AlN and GaN IIR are fitted to the Keldysh formula.
Kletsov, Aleksey A; Glukhovskoy, Evgeny G; Chumakov, Aleksey S; Ortiz, Joseph V
2016-01-01
The conduction properties of DNA molecule, particularly its transverse conductance (electron transfer through nucleotide bridges), represent a point of interest for DNA chemistry community, especially for DNA sequencing. However, there is no fully developed first-principles theory for molecular conductance and current that allows one to analyze the transverse flow of electrical charge through a nucleotide base. We theoretically investigate the transverse electron transport through all four DNA nucleotide bases by implementing an unbiased ab initio theoretical approach, namely, the electron propagator theory. The electrical conductance and current through DNA nucleobases (guanine [G], cytosine [C], adenine [A] and thymine [T]) inserted into a model 1-nm Ag-Ag nanogap are calculated. The magnitudes of the calculated conductance and current are ordered in the following hierarchies: gA>gG>gC>gT and IG>IA>IT>IC correspondingly. The new distinguishing parameter for the nucleobase identification is proposed, namely, the onset bias magnitude. Nucleobases exhibit the following hierarchy with respect to this parameter: Vonset(A)DNA translocation through an electrode-equipped nanopore. The results represent interest for the theorists and practitioners in the field of third generation sequencing techniques as well as in the field of DNA chemistry. Copyright © 2015 Elsevier B.V. All rights reserved.
Chrostowska, Anna; Nguyen, Thi Xuan Mai; Dargelos, Alain; Khayar, Saïd; Graciaa, Alain; Guillemin, Jean-Claude
2009-03-19
Beta-heterosubstituted acrylonitriles correspond to the formal addition of nucleophiles on cyanoacetylene. Acrylonitriles substituted with an amino, methoxy, mercapto group, or halogeno atom have been synthesized. Rearrangements between Z and E stereoisomers or tautomerizations have been studied by NMR spectroscopy and by quantum calculations. The photoelectron spectra were recorded and analyzed with the aid of a time-dependent density functional theory, ab initio OVGF, and so-called "corrected" ionization energy calculations. The electronic structure of the studied species was determined, and strong differences between beta-heterosubstituted acrylonitriles and the corresponding nitrile-free heteroalkenes were clearly documented. A "push-pull" effect was noticed, due to the combined donor effect of the substituent on one side of the carbon-carbon double bond and the electron-withdrawing effect of the nitrile group on the other side. Thus, the presence of a nitrile group strongly stabilizes the electronic structure. The efficient pi-donor contribution of the NH(2) and SH groups was evidenced.
Chan, EuJin; Lydon, Jenny; Kron, Tomas
2015-03-07
This study aims to investigate the effects of oblique incidence, small field size and inhomogeneous media on the electron dose distribution, and to compare calculated (Elekta/CMS XiO) and measured results. All comparisons were done in terms of absolute dose. A new measuring method was developed for high resolution, absolute dose measurement of non-standard beams using Gafchromic® EBT3 film. A portable U-shaped holder was designed and constructed to hold EBT3 films vertically in a reproducible setup submerged in a water phantom. The experimental film method was verified with ionisation chamber measurements and agreed to within 2% or 1 mm. Agreement between XiO electron Monte Carlo (eMC) and EBT3 was within 2% or 2 mm for most standard fields and 3% or 3 mm for the non-standard fields. Larger differences were seen in the build-up region where XiO eMC overestimates dose by up to 10% for obliquely incident fields and underestimates the dose for small circular fields by up to 5% when compared to measurement. Calculations with inhomogeneous media mimicking ribs, lung and skull tissue placed at the side of the film in water agreed with measurement to within 3% or 3 mm. Gafchromic film in water proved to be a convenient high spatial resolution method to verify dose distributions from electrons in non-standard conditions including irradiation in inhomogeneous media.
Energy Technology Data Exchange (ETDEWEB)
Sesion Jr, P D [Escola de Ciencias e Tecnologia, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, Rio Grande do Norte (Brazil); Henriques, J M [Departamento de Fisica Teorica e Experimental, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, Rio Grande do Norte (Brazil); Barboza, C A; Albuquerque, E L [Departamento de Biofisica e Farmacologia, Universidade Federal do Rio Grande do Norte, 59072-900 Natal, Rio Grande do Norte (Brazil); Freire, V N [Departamento de Fisica, Universidade Federal do Ceara, 60455-970 Fortaleza, Ceara (Brazil); Caetano, E W S, E-mail: ewcaetano@gmail.co [Instituto Federal de Educacao, Ciencia e Tecnologia do Ceara, Avenida 13 de Maio, 2081, Benfica, 60040-531 Fortaleza, Ceara (Brazil)
2010-11-03
CdSnO{sub 3} ilmenite and perovskite crystals were investigated using both the local density and generalized gradient approximations, LDA and GGA, respectively, of the density functional theory (DFT). The electronic band structures, densities of states, dielectric functions, optical absorption and reflectivity spectra related to electronic transitions were obtained, as well as the infrared absorption spectra after computing the vibrational modes of the crystals at q = 0. Dielectric optical permittivities and polarizabilities at {omega} = 0 and {infinity} were also calculated. The results show that GGA-optimized geometries are more accurate than LDA ones, and the Kohn-Sham band structures obtained for the CdSnO{sub 3} polymorphs confirm that ilmenite has an indirect band gap, while perovskite has a direct band gap, both being semiconductors. Effective masses for both crystals are obtained for the first time, being highly isotropic for electrons and anisotropic for holes. The optical properties reveal a very small degree of anisotropy of both crystals with respect to different polarization planes of incident light. The phonon calculation at q = 0 for perovskite CdSnO{sub 3} does not show any imaginary frequencies, in contrast to a previous report suggesting the existence of a more stable crystal of perovskite CdSnO{sub 3} with ferroelectric properties.
First-principles calculation of electronic energy level alignment at electrochemical interfaces
Azar, Yavar T.; Payami, Mahmoud
2017-08-01
Energy level alignment at solid-solvent interfaces is an important step in determining the properties of electrochemical systems. The positions of conduction and valence band edges of a semiconductor are affected by its environment. In this study, using first-principles DFT calculation, we have determined the level shifts of the semiconductors TiO2 and ZnO at the interfaces with MeCN and DMF solvent molecules. The level shifts of semiconductor are obtained using the potential difference between the clean and exposed surfaces of asymmetric slabs. In this work, neglecting the effects of present ions in the electrolyte solution, we have shown that the solvent molecules give rise to an up-shift for the levels, and the amount of this shift varies with coverage. It is also shown that the shapes of density of states do not change sensibly near the gap. Molecular dynamics simulations of the interface have shown that at room temperatures the semiconductor surface is not fully covered by the solvent molecules, and one must use intermediate values in an static calculations.
Ono, Tomoya; Tsukamoto, Shigeru
2016-01-01
We present a fast and stable numerical technique to obtain the self-energy terms of electrodes for first-principles electron transport calculations. Although first-principles calculations based on the real-space finite-difference method are advantageous for execution on massively parallel computers, large-scale transport calculations are hampered by the computational cost and numerical instability of the computation of the self-energy terms. Using the orthogonal complement vectors of the space spanned by the generalized Bloch waves that actually contribute to transport phenomena, the computational accuracy of transport properties is significantly improved with a moderate computational cost. To demonstrate the efficiency of the present technique, the electron transport properties of a Stone-Wales (SW) defect in graphene and silicene are examined. The resonance scattering of the SW defect is observed in the conductance spectrum of silicene since the σ* state of silicene lies near the Fermi energy. In addition, we found that one conduction channel is sensitive to a defect near the Fermi energy, while the other channel is hardly affected. This characteristic behavior of the conduction channels is interpreted in terms of the bonding network between the bilattices of the honeycomb structure in the formation of the SW defect. The present technique enables us to distinguish the different behaviors of the two conduction channels in graphene and silicene owing to its excellent accuracy.
First-Principles Electronic Structure Calculations of N2H4 Adsorbed on Single-Wall Carbon Nanotubes
Yu, M.; Tian, W. Q.; Jayanthi, C. S.; Wu, S. Y.
2008-03-01
Recent experiments conducted by Desai et al. [1] reveal that single-wall carbon nanotube (SWCNT) networks exposed to N2H4 vapor at various pressures exhibit considerable drop in resistance with respect to the pristine sample. Experimental findings reveal: (i) n-type behavior for the adsorption of N2H4/SWCNT, and (ii) the binding of N2H4 on SWCNT as chemisorption. In the present work, we have performed first-principles electronic structure calculations [2] for the N2H4 adsorbed on the (14, 0) SWCNT, where several orientations for the N2H4 molecule were considered. Calculations for the combined system were performed using 3 unit cells with the DFT/GGA and ultra soft pseudo-potentials. Our calculations reveal: (i) the binding of N2H4 on SWCNT as physisorption, and (ii) the electronic structure of SWCNT to be practically unaltered by the adsorption of N2H4, suggesting that there will not be a dramatic drop in resistance for N2H4/SWCNT. This is in disagreement with the experimental findings. To further understand the experimental observations, we will discuss mechanisms that may alter the binding nature of N2H4 on SWCNT. [1] S. Desai, G. Sumanasekera, et al. (APS, March 2008). [2] G. Kresse and J. Furthmuller, Phys. Rev. B 54, 11169 (1996).
Xiong, Huihui; Liu, Zhao; Zhang, Henghua; Du, Zheng; Chen, Congmei
2017-08-01
Interfacial models of SiC/ZrB2 composite coating were studied by first-principles calculations based on density functional theory (DFT). The cubic SiC and hexagonal ZrB2 were selected in our work, and twelve types of SiC (111)/ZrB2 (0001) interface structures were investigated in consideration of four different terminations and three stacking sequences. The cohesive energy (Wad), interfacial energy (γint), and electronic structure of the SiC/ZrB2 interfaces were all calculated. The results show that the ZrB2 (0001) surface with 9 layers exhibits bulk-like interior characteristic. Among the interfaces of C/Zr terminated hcp-stacked (CZH), Si/Zr terminated hcp-stacked (SZH), C/B terminated center-stacked (CBC) and Si/B terminated center-stacked (SBT), the CZH interface has the largest Wad (6.28 J/m2) and thus is of the best stability. Over the range of zirconium chemical potential, the γint of CZH, SZH, CBC and SBT interfaces are -0.31-2.50 J/m2, 1.07-3.88 J/m2, 2.85-5.66 J/m2 and 2.32-5.13 J/m2, respectively. The calculated electronic properties reveal that, the CZH, CBC and SBT interfaces mainly contain covalent bonding, while the SZH one primarily consists of metallic bonding.
Mairani, A; Valente, M; Battistoni, G; Botta, F; Pedroli, G; Ferrari, A; Cremonesi, M; Di Dia, A; Ferrari, M; Fasso, A
2011-01-01
Purpose: The calculation of patient-specific dose distribution can be achieved by Monte Carlo simulations or by analytical methods. In this study, FLUKA Monte Carlo code has been considered for use in nuclear medicine dosimetry. Up to now, FLUKA has mainly been dedicated to other fields, namely high energy physics, radiation protection, and hadrontherapy. When first employing a Monte Carlo code for nuclear medicine dosimetry, its results concerning electron transport at energies typical of nuclear medicine applications need to be verified. This is commonly achieved by means of calculation of a representative parameter and comparison with reference data. Dose point kernel (DPK), quantifying the energy deposition all around a point isotropic source, is often the one. Methods: FLUKA DPKS have been calculated in both water and compact bone for monoenergetic electrons (10-3 MeV) and for beta emitting isotopes commonly used for therapy ((89)Sr, (90)Y, (131)I, (153)Sm, (177)Lu, (186)Re, and (188)Re). Point isotropic...
Energy Technology Data Exchange (ETDEWEB)
Bouhemadou, A. [Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria)], E-mail: a_bouhemadou@yahoo.fr; Khenata, R. [Department of Physics, University of Mascara, 29000 Mascara (Algeria); Chegaar, M.; Maabed, S. [Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria)
2007-11-19
The density functional theory (DFT) calculations of structural, elastic, electronic and optical properties of the cubic antiperovskite AsNMg{sub 3} has been reported using the pseudo-potential plane wave method (PP-PW) within the generalized gradient approximation (GGA). The equilibrium lattice, bulk modulus and its pressure derivative have been determined. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young's modulus and Poisson's ratio for ideal polycrystalline AsNMg{sub 3} aggregate. We estimated the Debye temperature of AsNMg{sub 3} from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of AsNMg{sub 3} compound, and it still awaits experimental confirmation. Band structure, density of states and pressure coefficients of energy gaps are also given. The fundamental band gap ({gamma}-{gamma}) initially increases up to 4 GPa and then decreases as a function of pressure. Furthermore, the dielectric function, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 30 eV. The all results are compared with the available theoretical and experimental data.
Energy Technology Data Exchange (ETDEWEB)
Du, Jincheng; Devanathan, Ramaswami; Corrales, Louis R.; Weber, William J.
2012-05-01
First-principles periodic density functional theory (DFT) calculations have been performed to understand the electronic structure, chemical bonding, phase transition, and physical properties of the mineral zircon (in the chemical composition of ZrSiO4) and its high pressure phase reidite. Temperature effect on phase transition and thermal–mechanical properties such as heat capacity and bulk modulus have been studied by combining the equation of states obtained from DFT calculations with the quasi-harmonic Debye model to take into account the entropy contribution to free energy. Local density approximation (LDA) and generalized gradient approximation (GGA) DFT functionals have been systematically compared in predicting the structure and property of this material. It is found that the LDA functional provides a better description of the equilibrium structure and bulk modulus, while GGA predicts a transition pressure closer to experimental values. Both functionals correctly predict the relative stability of the two phases, with GGA giving slightly larger energy differences. The calculated band structures show that both zircon and reidite have indirect bandgaps and the reidite phase has a narrower bandgap than the zircon phase. The electronic density of states and atomic charges analyses show that bonding in the high-pressure reidite phase has a stronger covalent character.
Energy Technology Data Exchange (ETDEWEB)
Habib, B.; Poumarede, B.; Tola, F.; Barthe, J. [CEA, LIST, Dept Technol Capteur et Signal, F-91191 Gif Sur Yvette, (France)
2010-07-01
The aim of the present study is to demonstrate the potential of accelerated dose calculations, using the fast Monte Carlo (MC) code referred to as PENFAST, rather than the conventional MC code PENELOPE, without losing accuracy in the computed dose. For this purpose, experimental measurements of dose distributions in homogeneous and inhomogeneous phantoms were compared with simulated results using both PENELOPE and PENFAST. The simulations and experiments were performed using a Saturne 43 linac operated at 12 MV (photons), and at 18 MeV (electrons). Pre-calculated phase space files (PSFs) were used as input data to both the PENELOPE and PENFAST dose simulations. Since depth-dose and dose profile comparisons between simulations and measurements in water were found to be in good agreement (within {+-} 1% to 1 mm), the PSF calculation is considered to have been validated. In addition, measured dose distributions were compared to simulated results in a set of clinically relevant, inhomogeneous phantoms, consisting of lung and bone heterogeneities in a water tank. In general, the PENFAST results agree to within a 1% to 1 mm difference with those produced by PENELOPE, and to within a 2% to 2 mm difference with measured values. Our study thus provides a pre-clinical validation of the PENFAST code. It also demonstrates that PENFAST provides accurate results for both photon and electron beams, equivalent to those obtained with PENELOPE. CPU time comparisons between both MC codes show that PENFAST is generally about 9-21 times faster than PENELOPE. (authors)
Lo, Po-Kam; Lau, Kai-Chung
2014-04-03
The ionization energy (IE), electron affinity (EA), and heats of formation (ΔH°f0/ΔH°f298) for cyclopentadienyl radical, cation, and anion, C5H5/C5H5(+)/C5H5(-), have been calculated by wave function-based ab initio CCSDT/CBS approach, which involves approximation to complete basis set (CBS) limit at coupled-cluster level with up to full triple excitations (CCSDT). The zero-point vibrational energy correction, core-valence electronic correction, scalar relativistic effect, and higher-order corrections beyond the CCSD(T) wave function are included in these calculations. The allylic [C5H5((2)A2)] and dienylic [C5H5((2)B1)] forms of cyclopentadienyl radical are considered: the ground state structure exists in the dienyl form and it is about 30 meV more stable than the allylic structure. Both structures are lying closely and are interconvertible along the normal mode of b2 in-plane vibration. The CCSDT/CBS predictions (in eV) for IE[C5H5(+)((3)A1')←C5H5((2)B1)] = 8.443, IE[C5H5(+)((1)A1)←C5H5((2)B1)] = 8.634 and EA[C5H5(-)((1)A1')←C5H5((2)B1)] = 1.785 are consistent with the respective experimental values of 8.4268 ± 0.0005, 8.6170 ± 0.0005, and 1.808 ± 0.006, obtained from photoelectron spectroscopic measurements. The ΔH°f0/ΔH°f298's (in kJ/mol) for C5H5/C5H5(+)/C5H5(-) have also been predicted by the CCSDT/CBS method: ΔH°f0/ΔH°f298[C5H5((2)B1)] = 283.6/272.0, ΔH°f0/ΔH°f298[C5H5(+)((3)A1')] = 1098.2/1086.9, ΔH°f0/ΔH°f298[C5H5(+)((1)A1)] = 1116.6/1106.0, and ΔH°f0/ΔH°f298[C5H5(-)((1)A1')] = 111.4/100.0. The comparisons between the CCSDT/CBS predictions and the experimental values suggest that the CCSDT/CBS procedure is capable of predicting reliable IE(C5H5)'s and EA(C5H5) with uncertainties of ± 17 and ± 23 meV, respectively.
Voltage profile, structural prediction, and electronic calculations for MgxMo6S8
CSIR Research Space (South Africa)
Kganyago, KR
2003-03-01
Full Text Available suggests a maximum uptake formally of two Mg ions into the electron-de?cient Mo6 cluster, which leaves us with two possible vacant sites: the inner Li1 site ~substituted by MgA) close to the unit-cell origin with the atom coordinates (0.598,0.359,0.381:b52... be de?ned with Mg0 being the origin. The vector from Mg0 to Mg1 is the c lattice parameter and the vectors from Mg0 to Mg2 and Mg0 to Mg3 are the a lattice parameters. K. R. KGANYAGO, P. E. NGOEPE, AND C. R. A. CATLOW PHYSICAL REVIEW B 67, 104103 ~2003...
GPAW - massively parallel electronic structure calculations with Python-based software
DEFF Research Database (Denmark)
Enkovaara, Jussi; Romero, Nichols A.; Shende, Sameer
2011-01-01
popular choice. While dynamic, interpreted languages, such as Python, can increase the effciency of programmer, they cannot compete directly with the raw performance of compiled languages. However, by using an interpreted language together with a compiled language, it is possible to have most...... of the productivity enhancing features together with a good numerical performance. We have used this approach in implementing an electronic structure simulation software GPAW using the combination of Python and C programming languages. While the chosen approach works well in standard workstations and Unix...... environments, massively parallel supercomputing systems can present some challenges in porting, debugging and profiling the software. In this paper we describe some details of the implementation and discuss the advantages and challenges of the combined Python/C approach. We show that despite the challenges...
Electron-phonon scattering rates in complex polar crystals from ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Prange, Micah P.; Campbell, Luke W.; Kerisit, Sebastien N.
2017-09-17
The thermalization of fast electrons by phonons is studied in CsI, NaI, SrI2, and YAP. This numerical study uses an improvement to a recently developed ab initio method based on a density functional perturbation theoretical description of the phonon modes that provides a way to go beyond widely used phonon models based on binary crystals. Improvements to this method are described, and scattering rates are presented and discussed. The results here treat polar and nonpolar scattering on equal footing and allow an assessment of the relative importance of the two types of scattering. The relative activity of the numerous phonon modes in materials with complicated structures is discussed, and a simple criterion for finding the modes that scatter strongly is presented.
Calculation of Electronic and Optical Properties of Doped Titanium Dioxide Nanostructure
Directory of Open Access Journals (Sweden)
Sh. Khaleghi
2012-06-01
Full Text Available By means of first principles calculations we show that both rutile and anatase phases of bulk TiO2 doped by S, Se or Pb can display substantial decreasing in the band gap (up to 50%, while doping by Zr does not sizably affect the band-gap value. Moreover, the absorption edge is shifted (up to 1 eV to the lower energy range in the case of TiO2 doped by S or Pb that opens a way to enhancing of absorption of sun’s radiation. We also discuss how our findings can improve efficiency of photovoltaic cells and photocatalytic cells for hydrogen generation.
Pashov, A D; Calvez, T; Gilardin, L; Maillère, B; Repessé, Y; Oldenburg, J; Pavlova, A; Kaveri, S V; Lacroix-Desmazes, S
2014-03-01
Forty per cent of haemophilia A (HA) patients have missense mutations in the F8 gene. Yet, all patients with identical mutations are not at the same risk of developing factor VIII (FVIII) inhibitors. In severe HA patients, human leucocyte antigen (HLA) haplotype was identified as a risk factor for onset of FVIII inhibitors. We hypothesized that missense mutations in endogenous FVIII alter the affinity of the mutated peptides for HLA class II, thus skewing FVIII-specific T-cell tolerance and increasing the risk that the corresponding wild-type FVIII-derived peptides induce an anti-FVIII immune response during replacement therapy. Here, we investigated whether affinity for HLA class II of wild-type FVIII-derived peptides that correspond to missense mutations described in the Haemophilia A Mutation, Structure, Test and Resource database is associated with inhibitor development. We predicted the mean affinity for 10 major HLA class II alleles of wild-type FVIII-derived peptides that corresponded to 1456 reported cases of missense mutations. Linear regression analysis confirmed a significant association between the predicted mean peptide affinity and the mutation inhibitory status (P = 0.006). Significance was lost after adjustment on mutation position on FVIII domains. Although analysis of the A1-A2-A3-C1 domains yielded a positive correlation between predicted HLA-binding affinity and inhibitory status (OR = 0.29 [95% CI: 0.14-0.60] for the high affinity tertile, P = 0.002), the C2 domain-restricted analysis indicated an inverse correlation (OR = 3.56 [1.10-11.52], P = 0.03). Our data validate the importance of the affinity of FVIII peptides for HLA alleles to the immunogenicity of therapeutic FVIII in patients with missense mutations. © 2013 John Wiley & Sons Ltd.
Energy Technology Data Exchange (ETDEWEB)
Lee, Y.S.
1977-11-01
The effects of the 4f shell of electrons and the relativity of valence electrons are compared. The effect of 4f shell (lanthanide contraction) is estimated from the numerical Hartree-Fock (HF) calculations of pseudo-atoms corresponding to Hf, Re, Au, Hg, Tl, Pb and Bi without 4f electrons and with atomic numbers reduced by 14. The relativistic effect estimated from the numerical Dirac-Hartree-Fock (DHF) calculations of those atoms is comparable in the magnitude with that of the 4f shell of electrons. Both are larger for 6s than for 5d or 6p electrons. The various relativistic effects on valence electrons are discussed in detail to determine the proper level of the approximation for the valence electron calculations of systems with heavy elements. An effective core potential system has been developed for heavy atoms in which relativistic effects are included in the effective potentials.
da Silva, E. Lora; Marinopoulos, A. G.; Vieira, R. B. L.; Vilão, R. C.; Alberto, H. V.; Gil, J. M.; Lichti, R. L.; Mengyan, P. W.; Baker, B. B.
2016-07-01
The electronic structure of hydrogen impurity in Lu2O3 was studied by first-principles calculations and muonium spectroscopy. The computational scheme was based on two methods which are well suited to treat defect calculations in f -electron systems: first, a semilocal functional of conventional density-functional theory (DFT) and secondly a DFT+U approach which accounts for the on-site correlation of the 4 f electrons via an effective Hubbard-type interaction. Three different types of stable configurations were found for hydrogen depending upon its charge state. In its negatively charged and neutral states, hydrogen favors interstitial configurations residing either at the unoccupied sites of the oxygen sublattice or at the empty cube centers surrounded by the lanthanide ions. In contrast, the positively charged state stabilized only as a bond configuration, where hydrogen binds to oxygen ions. Overall, the results between the two methods agree in the ordering of the formation energies of the different impurity configurations, though within DFT+U the charge-transition (electrical) levels are found at Fermi-level positions with higher energies. Both methods predict that hydrogen is an amphoteric defect in Lu2O3 if the lowest-energy configurations are used to obtain the charge-transition, thermodynamic levels. The calculations of hyperfine constants for the neutral interstitial configurations show a predominantly isotropic hyperfine interaction with two distinct values of 926 MHz and 1061 MHz for the Fermi-contact term originating from the two corresponding interstitial positions of hydrogen in the lattice. These high values are consistent with the muonium spectroscopy measurements which also reveal a strongly isotropic hyperfine signature for the neutral muonium fraction with a magnitude slightly larger (1130 MHz) from the ab initio results (after scaling with the magnetic moments of the respective nuclei).
Wiktor, Julia; Jomard, Gérald; Torrent, Marc; Bertolus, Marjorie
2017-01-01
We performed first-principles calculations of the momentum distributions of annihilating electron-positron pairs in vacancies in uranium dioxide. Full atomic relaxation effects (due to both electronic and positronic forces) were taken into account and self-consistent two-component density functional theory schemes were used. We present one-dimensional momentum distributions (Doppler-broadened annihilation radiation line shapes) along with line-shape parameters S and W. We studied the effect of the charge state of the defect on the Doppler spectra. The effect of krypton incorporation in the vacancy was also considered and it was shown that it should be possible to observe the fission gas incorporation in defects in UO2 using positron annihilation spectroscopy. We suggest that the Doppler broadening measurements can be especially useful for studying impurities and dopants in UO2 and of mixed actinide oxides.
Energy Technology Data Exchange (ETDEWEB)
Botta, F.; Mairani, A.; Battistoni, G.; Cremonesi, M.; Di Dia, A.; Fasso, A.; Ferrari, A.; Ferrari, M.; Paganelli, G.; Pedroli, G.; Valente, M. [Medical Physics Department, European Institute of Oncology, Via Ripamonti 435, 20141 Milan (Italy); Istituto Nazionale di Fisica Nucleare (I.N.F.N.), Via Celoria 16, 20133 Milan (Italy); Medical Physics Department, European Institute of Oncology, Via Ripamonti 435, 20141 Milan (Italy); Jefferson Lab, 12000 Jefferson Avenue, Newport News, Virginia 23606 (United States); CERN, 1211 Geneva 23 (Switzerland); Medical Physics Department, European Institute of Oncology, Milan (Italy); Nuclear Medicine Department, European Institute of Oncology, Via Ripamonti 435, 2014 Milan (Italy); Medical Physics Department, European Institute of Oncology, Via Ripamonti 435, 20141 Milan (Italy); FaMAF, Universidad Nacional de Cordoba and CONICET, Cordoba, Argentina C.P. 5000 (Argentina)
2011-07-15
Purpose: The calculation of patient-specific dose distribution can be achieved by Monte Carlo simulations or by analytical methods. In this study, fluka Monte Carlo code has been considered for use in nuclear medicine dosimetry. Up to now, fluka has mainly been dedicated to other fields, namely high energy physics, radiation protection, and hadrontherapy. When first employing a Monte Carlo code for nuclear medicine dosimetry, its results concerning electron transport at energies typical of nuclear medicine applications need to be verified. This is commonly achieved by means of calculation of a representative parameter and comparison with reference data. Dose point kernel (DPK), quantifying the energy deposition all around a point isotropic source, is often the one. Methods: fluka DPKs have been calculated in both water and compact bone for monoenergetic electrons (10{sup -3} MeV) and for beta emitting isotopes commonly used for therapy ({sup 89}Sr, {sup 90}Y, {sup 131}I, {sup 153}Sm, {sup 177}Lu, {sup 186}Re, and {sup 188}Re). Point isotropic sources have been simulated at the center of a water (bone) sphere, and deposed energy has been tallied in concentric shells. fluka outcomes have been compared to penelope v.2008 results, calculated in this study as well. Moreover, in case of monoenergetic electrons in water, comparison with the data from the literature (etran, geant4, mcnpx) has been done. Maximum percentage differences within 0.8{center_dot}R{sub CSDA} and 0.9{center_dot}R{sub CSDA} for monoenergetic electrons (R{sub CSDA} being the continuous slowing down approximation range) and within 0.8{center_dot}X{sub 90} and 0.9{center_dot}X{sub 90} for isotopes (X{sub 90} being the radius of the sphere in which 90% of the emitted energy is absorbed) have been computed, together with the average percentage difference within 0.9{center_dot}R{sub CSDA} and 0.9{center_dot}X{sub 90} for electrons and isotopes, respectively. Results: Concerning monoenergetic electrons
Barmashenko, B. D.; Rosenwaks, S.; Heaven, M. C.
2013-04-01
The effects of heating, ionization, high electronic excitation and chemical reactions on the operation of diode pumped alkali lasers (DPALs) with a static, non-flowing gain medium are calculated using a semi-analytical model. Unlike other models, assuming a three-level scheme of the laser and neglecting influence of the temperature on the lasing power, it takes into account the temperature rise and losses of neutral alkali atoms due to ionization and chemical reactions, resulting in decrease of the pump absorption and slope efficiency. Good agreement with measurements in a static DPAL [B.V. Zhdanov, J. Sell, R.J. Knize, Electron. Lett. 44 (2008) 582] is obtained. It is found that the ionization processes have a small effect on the laser operation, whereas the chemical reactions of alkali atoms with hydrocarbons strongly affect the lasing power.
Bettahar, N.; Nasri, D.; Benalia, S.; Merabet, M.; Abidri, B.; Benkhettou, N.; Khenata, R.; Rached, D.; Rabah, M.
2013-03-01
Elastic, thermodynamic, electronic, and magnetic properties in the cubic antiperovskite InNCe3 compound are derived from the full-potential linear muffin-tin orbital method. From the computed elastic constants, theoretical values of Young's modulus, the shear modulus, Poisson's ratio, Lamé's coefficients, sound velocities, and the Debye temperature are evaluated. Analysis of the ratio between the bulk modulus and the shear modulus shows that InNCe3 is brittle in nature. The variations of elastic constants with pressure indicate that this compound possesses higher mechanical stability in the pressure range from 0 to 40 GPa. The electronic and magnetic properties of this compound are calculated by adding the Coulomb interaction U to improve the results.
Botta, F; Mairani, A; Battistoni, G; Cremonesi, M; Di Dia, A; Fassò, A; Ferrari, A; Ferrari, M; Paganelli, G; Pedroli, G; Valente, M
2011-07-01
The calculation of patient-specific dose distribution can be achieved by Monte Carlo simulations or by analytical methods. In this study, FLUKA Monte Carlo code has been considered for use in nuclear medicine dosimetry. Up to now, FLUKA has mainly been dedicated to other fields, namely high energy physics, radiation protection, and hadrontherapy. When first employing a Monte Carlo code for nuclear medicine dosimetry, its results concerning electron transport at energies typical of nuclear medicine applications need to be verified. This is commonly achieved by means of calculation of a representative parameter and comparison with reference data. Dose point kernel (DPK), quantifying the energy deposition all around a point isotropic source, is often the one. FLUKA DPKS have been calculated in both water and compact bone for monoenergetic electrons (10-3 MeV) and for beta emitting isotopes commonly used for therapy (89Sr, 90Y, 131I 153Sm, 177Lu, 186Re, and 188Re). Point isotropic sources have been simulated at the center of a water (bone) sphere, and deposed energy has been tallied in concentric shells. FLUKA outcomes have been compared to PENELOPE v.2008 results, calculated in this study as well. Moreover, in case of monoenergetic electrons in water, comparison with the data from the literature (ETRAN, GEANT4, MCNPX) has been done. Maximum percentage differences within 0.8.RCSDA and 0.9.RCSDA for monoenergetic electrons (RCSDA being the continuous slowing down approximation range) and within 0.8.X90 and 0.9.X90 for isotopes (X90 being the radius of the sphere in which 90% of the emitted energy is absorbed) have been computed, together with the average percentage difference within 0.9.RCSDA and 0.9.X90 for electrons and isotopes, respectively. Concerning monoenergetic electrons, within 0.8.RCSDA (where 90%-97% of the particle energy is deposed), FLUKA and PENELOPE agree mostly within 7%, except for 10 and 20 keV electrons (12% in water, 8.3% in bone). The
Halim, Shimaa Abdel; Khalil, Ali Kh.
2017-11-01
The electronic structure of thiazolo[3,2-a]pyridine and some of its derivatives are investigated theoretically using B3LYB/6-311G (d, p) method. The calculations show that all the studied compounds 1-5 are non-planar, as indicated from the dihedral angles. The electronic absorption spectra of the studied compounds are recorded in the UV-VIS region, in both DMF and Dioxane solvents. Assignments of the observed electronic transitions are facilitated via time-dependent density functional theory (TD-DFT) computations. Band maxima (λmax) and intensities of the spectra are found to have solvent dependence reflected as blue and red shifts. Electronic configurations contributing to each excited state are identified and the relevant MOs are characterized. The extent of delocalization and intermolecular charge transfer are estimated and discussed in terms of natural bond orbital (NBO) analysis and second order perturbation interactions between donor and acceptor MOs. The theoretical spectra computed at ;A new hybrid exchange-correlation functional using the Coulomb-attenuating method (CAM-B3LYP),; at the 6-311G (d, p) bases set in gas phase and with the Polarizable Continuum Model (PCM) in Dioxane and DMF indicate a good agreement with the observed spectra.
Accuracy and Transferability of Ab Initio Electronic Band Structure Calculations for Doped BiFeO3
Gebhardt, Julian; Rappe, Andrew M.
2017-11-01
BiFeO3 is a multiferroic material and, therefore, highly interesting with respect to future oxide electronics. In order to realize such devices, pn junctions need to be fabricated, which are currently impeded by the lack of successful p-type doping in this material. In order to guide the numerous research efforts in this field, we recently finished a comprehensive computational study, investigating the influence of many dopants onto the electronic structure of BiFeO3. In order to allow for this large scale ab initio study, the computational setup had to be accurate and efficient. Here we discuss the details of this assessment, showing that standard density-functional theory (DFT) yields good structural properties. The obtained electronic structure, however, suffers from well-known shortcomings. By comparing the conventional DFT results for alkali and alkaline-earth metal doping with more accurate hybrid-DFT calculations, we show that, in this case, the problems of standard DFT go beyond a simple systematic error. Conventional DFT shows bad transferability and the more reliable hybrid-DFT has to be chosen for a qualitatively correct prediction of doping induced changes in the electronic structure of BiFeO3.
Litsarev, Mikhail S.
2013-02-01
A description of the DEPOSIT computer code is presented. The code is intended to calculate total and m-fold electron-loss cross-sections (m is the number of ionized electrons) and the energy T(b) deposited to the projectile (positive or negative ion) during a collision with a neutral atom at low and intermediate collision energies as a function of the impact parameter b. The deposited energy is calculated as a 3D integral over the projectile coordinate space in the classical energy-deposition model. Examples of the calculated deposited energies, ionization probabilities and electron-loss cross-sections are given as well as the description of the input and output data. Program summaryProgram title: DEPOSIT Catalogue identifier: AENP_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AENP_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License version 3 No. of lines in distributed program, including test data, etc.: 8726 No. of bytes in distributed program, including test data, etc.: 126650 Distribution format: tar.gz Programming language: C++. Computer: Any computer that can run C++ compiler. Operating system: Any operating system that can run C++. Has the code been vectorised or parallelized?: An MPI version is included in the distribution. Classification: 2.4, 2.6, 4.10, 4.11. Nature of problem: For a given impact parameter b to calculate the deposited energy T(b) as a 3D integral over a coordinate space, and ionization probabilities Pm(b). For a given energy to calculate the total and m-fold electron-loss cross-sections using T(b) values. Solution method: Direct calculation of the 3D integral T(b). The one-dimensional quadrature formula of the highest accuracy based upon the nodes of the Yacobi polynomials for the cosθ=x∈[-1,1] angular variable is applied. The Simpson rule for the φ∈[0,2π] angular variable is used. The Newton-Cotes pattern of the seventh order
Powell, B J; Bernstein, N; Brake, K; McKenzie, Ross H; Meredith, P; Pederson, M R
2016-01-01
We report first principles density functional calculations for hydroquinone (HQ), indolequinone (IQ) and semiquinone (SQ). These molecules are believed to be the basic building blocks of the eumelanins, a class of bio-macromolecules with important biological functions (including photoprotection) and with potential for certain bioengineering applications. We have used the DeltaSCF (difference of self consistent fields) method to study the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), Delta_HL. We show that Delta_HL is similar in IQ and SQ but approximately twice as large in HQ. This may have important implications for our understanding of the observed broad band optical absorption of the eumelanins. The possibility of using this difference in Delta_HL to molecularly engineer the electronic properties of eumelanins is discussed. We calculate the infrared and Raman spectra of the three redox forms from first principles. Each of the molecules ...
Singh, Swapnil; Singh, Harshita; Srivastava, Anubha; Tandon, Poonam; Sinha, Kirti; Bharti, Purnima; Kumar, Sudhir; Kumar, Padam; Maurya, Rakesh
2014-11-11
In the present work, a detailed conformational study of cladrin (3-(3,4-dimethoxy phenyl)-7-hydroxychromen-4-one) has been done by using spectroscopic techniques (FT-IR/FT-Raman/UV-Vis/NMR) and quantum chemical calculations. The optimized geometry, wavenumber and intensity of the vibrational bands of the cladrin in ground state were calculated by density functional theory (DFT) employing 6-311++G(d,p) basis sets. The study has been focused on the two most stable conformers that are selected after the full geometry optimization of the molecule. A detailed assignment of the FT-IR and FT-Raman spectra has been done for both the conformers along with potential energy distribution for each vibrational mode. The observed and scaled wavenumber of most of the bands has been found to be in good agreement. The UV-Vis spectrum has been recorded and compared with calculated spectrum. In addition, 1H and 13C nuclear magnetic resonance spectra have been also recorded and compared with the calculated data that shows the inter or intramolecular hydrogen bonding. The electronic properties such as HOMO-LUMO energies were calculated by using time-dependent density functional theory. Molecular electrostatic potential has been plotted to elucidate the reactive part of the molecule. Natural bond orbital analysis was performed to investigate the molecular stability. Non linear optical property of the molecule have been studied by calculating the electric dipole moment (μ) and the first hyperpolarizability (β) that results in the nonlinearity of the molecule. Copyright © 2014 Elsevier B.V. All rights reserved.
Zhu, Jinhan; Chen, Lixin; Chen, Along; Luo, Guangwen; Deng, Xiaowu; Liu, Xiaowei
2015-04-11
To use a graphic processing unit (GPU) calculation engine to implement a fast 3D pre-treatment dosimetric verification procedure based on an electronic portal imaging device (EPID). The GPU algorithm includes the deconvolution and convolution method for the fluence-map calculations, the collapsed-cone convolution/superposition (CCCS) algorithm for the 3D dose calculations and the 3D gamma evaluation calculations. The results of the GPU-based CCCS algorithm were compared to those of Monte Carlo simulations. The planned and EPID-based reconstructed dose distributions in overridden-to-water phantoms and the original patients were compared for 6 MV and 10 MV photon beams in intensity-modulated radiation therapy (IMRT) treatment plans based on dose differences and gamma analysis. The total single-field dose computation time was less than 8 s, and the gamma evaluation for a 0.1-cm grid resolution was completed in approximately 1 s. The results of the GPU-based CCCS algorithm exhibited good agreement with those of the Monte Carlo simulations. The gamma analysis indicated good agreement between the planned and reconstructed dose distributions for the treatment plans. For the target volume, the differences in the mean dose were less than 1.8%, and the differences in the maximum dose were less than 2.5%. For the critical organs, minor differences were observed between the reconstructed and planned doses. The GPU calculation engine was used to boost the speed of 3D dose and gamma evaluation calculations, thus offering the possibility of true real-time 3D dosimetric verification.
Calculation of Electronic and Optical Properties of AgGaO2 Polymorphs Using Many-Body Approaches
Dadsetani, Mehrdad; Nejatipour, Reihan
2018-02-01
Ab initio calculations based on many-body perturbation theory have been used to study the electronic and optical properties of AgGaO2 in rhombohedral, hexagonal, and orthorhombic phases. GW calculations showed that AgGaO2 is an indirect-bandgap semiconductor in all three phases with energy bandgap of 2.35 eV, 2.23 eV, and 2.07 eV, in good agreement with available experimental values. By solving the Bethe-Salpeter equation (BSE) using the full potential linearized augmented plane wave basis, optical properties of the AgGaO2 polymorphs were calculated and compared with those obtained using the GW-corrected random phase approximation (RPA) and with existing experimental data. Strong anisotropy in the optical absorption spectra was observed, and the excitonic structures which were absent in the RPA calculations were reproduced in GWBSE calculations, in good agreement with the optical absorption spectrum of the rhombohedral phase. While modifying peak positions and intensities of the absorption spectra, the GWBSE gave rise to the redistribution of oscillator strengths. In comparison with the z-polarized response, excitonic effects in the x-polarized response were dominant. In the x- (and y-) polarized responses of r- and h-AgGaO2, spectral features and excitonic effects occur at the lower energies, but in the case of o-AgGaO2, the spectral structures of the z-polarized response occur at lower energies. In addition, the low-energy loss functions of AgGaO2 were calculated and compared using the GWBSE approach. Spectral features in the energy loss function components near the bandgap region were attributed to corresponding excitonic structures in the imaginary part of the dielectric function.
Hata, Toshiyuki; Murakami, Takahiro; Shibuya, Hirotaka; Ono, Yukio
2006-05-01
The NM-gamma CNDO/S program previously developed by our group was modified by the introduction of a new one-center electron repulsion integral gamma(AA)(new) approximation, namely, the gamma(AA)(new)-CNDO/S method. The value of this gamma(AA)(new) was evaluated according to the product values of the coefficient C with the gamma(AA) value proposed in our previous paper. This method using a new gamma(AA) was also found to improve the two-center electron repulsion integral gamma(AB) value with respect to the chemical softness proposed by Nishimoto and co-workers, together with the difference between HOMO and LUMO orbital energies. The results calculated by the present improved gamma(AA)(new)-CNDO/S method demonstrated that not only the calculated absorption maxima wavelengths and ionization potentials, but also the order and the assignment of orbitals coincided very well with those based on the results of experiments investigating a variety of polyenes, cyanynes, and polycyclic aromatic hydrocarbons.
Dias, Jerry Ray
2016-06-09
The results herein demonstrate that the methods of circumscribing and the facile calculation of Hückel molecular orbital (HMO) eigenvalues by mirror-plane fragmentation have a broad application in the construction of carbon cluster series and the systematic study of trends in their electronic properties. In comparing open-ended nanotubes and their isomeric elongated fullerenes (bicapped nanotubes), we show that the former are more aromatic but the latter are more conjugated and that progressive elongation increases aromaticity and conjugation in both. Recursion equations that will allow one to obtain the eigenvalues to all 5-endcapped nanotubes are given.
Haaland, Arne; Martinsen, Kjell-Gunnar; Tafipolsky, Maxim A.; Volden, Hans Vidar; Rösler, Roland; Breunig, Hans Joachim
1997-09-01
Ab initio calculations at the MP2 level and gas electron-diffraction data of (CH 3) 2TeCl 2 show that the molecular structure is pseudo-trigonal bipyramidal with the two methyl groups occupying equatorial positions and the two Cl atoms axial positions. The bond distances are ( {GED}/{MP2 }): TeC = 213.2(5)/214.6 pm, TeCl = 250.4(3)/261.8 pm and the valence angles ∠ CTeC = {97(5)°}/{97.6°}; ∠ ClTeCl = {170(2)°}/{170.8°}.
Azhar, N. S.; Taib, M. F. M.; Hassan, O. H.; Yahya, M. Z. A.; Ali, A. M. M.
2017-03-01
Crystal structures of α-Bi2O3 and β-Bi2O3 were calculated using Cambridge serial total energy package (CASTEP) based on the first-principles plane-wave ultrasoft pseudopotential method within local density approximation (LDA) and generalized gradient approximation (GGA) together with Perdew-Burke-Ernzerhof (GGA-PBE) and Perdew-Burke-Ernzerhof revised for solid (GGA-PBEsol). The structural parameter of α-Bi2O3 and β-Bi2O3 are in good agreement with previous experimental and theoretical data. All of the polymorphs were calculated for the total density of states (TDOS) and the partial density of states (PDOS) of Bi, O atoms. Density of states exhibits hybridization of Bi 6s and O 2p orbitals and the calculated charge density profiles exhibit the ionic character in the chemical bonding of this compound. The narrowed band gap (E g) and red-shift of light absorption edge are responsible for the photocatalytic activity of Bi2O3 for water splitting application. The optical properties such as optical absorption and electron energy loss function were calculated to show the best structure among these polymorphs for the photocatalytic water splitting application.
Energy Technology Data Exchange (ETDEWEB)
Lalic, M.V.; Carbonari, A.W.; Saxena, R.N.; Moralles, M.; Mestnik-Filho, J. [Instituto de Pesquisas Energeticas e Nucleares, Sao Paulo, SP (Brazil)]. E-mail: jmestnik@net.ipen.br
2002-06-10
We report on first-principles band-structure calculations of the semiconducting CuAlO{sub 2} delafossite compound in the pure form and also with Cd impurity occupying either a Cu or Al position. The computational tool was a full-potential linear augmented plane-wave method, with the generalized gradient approximation accounting for the exchange and correlation effects. The changes caused by the presence of Cd are studied by the analysis of the electronic structure and the electric field gradient (EFG) in both Cd-doped and pure CuAlO{sub 2} systems. Good agreement between the calculated and measured EFGs at Cd substituting for Cu or Al atoms in CuAlO{sub 2} indicates that the calculations were able to correctly describe the ground state of the system containing the impurity. It is shown that a specific hybridization scheme, involving Cu (and Cd) s and d{sub z{sup 2}} orbitals and neighbouring O p{sub z} orbitals, takes place at the Cu sites in CuAlO{sub 2} as proposed earlier. The results of the calculations indicate that the Cd-doped system changes its electrical properties when Cd replaces Cu atoms (producing an n-type semiconductor), but not when it substitutes for Al atoms. (author)
Energy Technology Data Exchange (ETDEWEB)
Liebscher, C.H.; Freysoldt, C. [Max-Planck-Institut für Eisenforschung GmbH, 40237 Düsseldorf (Germany); Dennenwaldt, T. [Institute of Condensed Matter Physics and Interdisciplinary Center for Electron Microscopy, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne (Switzerland); Harzer, T.P.; Dehm, G. [Max-Planck-Institut für Eisenforschung GmbH, 40237 Düsseldorf (Germany)
2017-07-15
Metastable Cu–Cr alloy thin films with nominal thickness of 300 nm and composition of Cu{sub 67}Cr{sub 33} (at%) are obtained by co-evaporation using molecular beam epitaxy. The microstructure, chemical phase separation and electronic structure are investigated by transmission electron microscopy (TEM). The thin film adopts the body-centered cubic crystal structure and consists of columnar grains with ~50 nm diameter. Aberration-corrected scanning TEM in combination with energy dispersive X-ray spectroscopy confirms compositional fluctuations within the grains. Cu- and Cr-rich domains with composition of Cu{sub 85}Cr{sub 15} (at%) and Cu{sub 42}Cr{sub 58} (at%) and domain size of 1–5 nm are observed. The alignment of the interface between the Cu- and Cr-rich domains shows a preference for {110}-type habit plane. The electronic structure of the Cu–Cr thin films is investigated by electron energy loss spectroscopy (EELS) and is contrasted to an fcc-Cu reference sample. The experimental EEL spectra are compared to spectra computed by density functional theory. The main differences between bcc-and fcc-Cu are related to differences in van Hove singularities in the electron density of states. In Cu–Cr solid solutions with bcc crystal structure a single peak after the L{sub 3}-edge, corresponding to a van Hove singularity at the N-point of the first Brillouin zone is observed. Spectra computed for pure bcc-Cu and random Cu–Cr solid solutions with 10 at% Cr confirm the experimental observations. The calculated spectrum for a perfect Cu{sub 50}Cr{sub 50} (at%) random structure shows a shift in the van Hove singularity towards higher energy by developing a Cu–Cr d-band that lies between the delocalized d-bands of Cu and Cr. - Highlights: • Compositional fluctuations on the order of 1–5 nm in Cu- and Cr-rich domains are observed. • EELS determines a single van Hove singularity for bcc Cu–Cr solid solutions. • The electronic structure is dominated by d
Structural and electronic properties of wurtzite Bx Al1-x N from first-principles calculations
Zhang, Muwei
2017-06-14
The structural and electronic properties of wurtzite BAlN (0≤x≤1) are studied using density functional theory. The change of lattice parameters with increased B composition shows small bowing parameters and thus slightly nonlinearity. The bandgap exhibits strong dependence on the B composition, where transition from direct to indirect bandgap occurs at a relatively low B composition (x∼0.12) is observed, above which the bandgap of BAlN maintained indirect, thus desirable for low-absorption optical structures. The Γ-A and Γ-K indirect bandgaps are dominant at lower and higher B compositions, respectively. Density of states (DOS) of the valence band is susceptible to the B incorporation. Strong hybridization of Al, B, and N in p-states leads to high DOS near the valence band maximum. The hybridization of Al and B in s-states at lower B compositions and p-states of B at higher B compositions give rise to high DOS near lower end of the upper valence band. Charge density analysis reveals the B-N chemical bond is more covalent than the Al-N bond. This will lead to more covalent crystal with increasing B composition. Dramatic change of the heavy hole effective mass is found due to significant curvature increase of the band by minor B incorporation.
Electronic Structure of Hydrogenated and Surface-Modified GaAs Nanocrystals: Ab Initio Calculations
Directory of Open Access Journals (Sweden)
Hamsa Naji Nasir
2012-01-01
Full Text Available Two methods are used to simulate electronic structure of gallium arsenide nanocrystals. The cluster full geometrical optimization procedure which is suitable for small nanocrystals and large unit cell that simulates specific parts of larger nanocrystals preferably core part as in the present work. Because of symmetry consideration, large unit cells can reach sizes that are beyond the capabilities of first method. The two methods use ab initio Hartree-Fock and density functional theory, respectively. The results show that both energy gap and lattice constant decrease in their value as the nanocrystals grow in size. The inclusion of surface part in the first method makes valence band width wider than in large unit cell method that simulates the core part only. This is attributed to the broken symmetry and surface passivating atoms that split surface degenerate states and adds new levels inside and around the valence band. Bond length and tetrahedral angle result from full geometrical optimization indicate good convergence to the ideal zincblende structure at the centre of hydrogenated nanocrystal. This convergence supports large unit cell methodology. Existence of oxygen atoms at nanocrystal surface melts down density of states and reduces energy gap.
Energy Technology Data Exchange (ETDEWEB)
Ahuja, Ushma [Department of Electrical Engineering, Veermata Jijabai Technological Institute, H. R. Mahajani Marg, Matunga (East), Mumbai 400019, Maharashtra (India); Kumar, Kishor; Joshi, Ritu [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India); Bhavsar, D.N. [Department of Physics, Bhavan' s Seth R.A. College of Science, Khanpur, Ahmedabad 380001, Gujarat (India); Heda, N.L., E-mail: nlheda@yahoo.co.in [Department of Pure and Applied Physics, University of Kota, Kota 324007, Rajasthan (India)
2016-07-01
We have employed linear combination of atomic orbitals (LCAO) method to compute the Mulliken’s population (MP), energy bands, density of states (DOS) and Compton profiles for hexagonal MoTeSe. The density functional theory (DFT) and hybridization of Hartree-Fock with DFT (B3LYP) have been used within the LCAO approximation. Performance of theoretical models has been tested by comparing the theoretical momentum densities with the experimental Compton profile of MoTeSe measured using {sup 137}Cs Compton spectrometer. It is seen that the B3LYP prescription gives a better agreement with the experimental data than other DFT based approximations. The energy bands and DOS depict an indirect band gap character in MoTeSe. In addition, a relative nature of bonding in MoTeSe and its isovalent MoTe{sub 2} is discussed in terms of equal-valence-electron-density (EVED) profiles. On the basis of EVED profiles it is seen that MoTeSe is more covalent than MoTe{sub 2}.
Zinoviev, A. N.; Nordlund, K.
2017-09-01
The interatomic potential determines the nuclear stopping power in materials. Most ion irradiation simulation models are based on the universal Ziegler-Biersack-Littmark (ZBL) potential (Ziegler et al., 1983), which, however, is an average and hence may not describe the stopping of all ion-material combinations well. Here we consider pair-specific interatomic potentials determined experimentally and by density-functional theory simulations with DMol approach (DMol software, 1997) to choose basic wave functions. The interatomic potentials calculated using the DMol approach demonstrate an unexpectedly good agreement with experimental data. Differences are mainly observed for heavy atom systems, which suggests they can be improved by extending a basis set and more accurately considering the relativistic effects. Experimental data prove that the approach of determining interatomic potentials from quasielastic scattering can be successfully used for modeling collision cascades in ion-solids collisions. The data obtained clearly indicate that the use of any universal potential is limited to internuclear distances R < 7 af (af is the Firsov length).
Electronic Structure Calculations of Hydrogen Storage in Lithium-Decorated Metal-Graphyne Framework.
Kumar, Sandeep; Dhilip Kumar, Thogluva Janardhanan
2017-08-30
Porous metal-graphyne framework (MGF) made up of graphyne linker decorated with lithium has been investigated for hydrogen storage. Applying density functional theory spin-polarized generalized gradient approximation with the Perdew-Burke-Ernzerhof functional containing Grimme's diffusion parameter with double numeric polarization basis set, the structural stability, and physicochemical properties have been analyzed. Each linker binds two Li atoms over the surface of the graphyne linker forming MGF-Li8 by Dewar coordination. On saturation with hydrogen, each Li atom physisorbs three H2 molecules resulting in MGF-Li8-H24. H2 and Li interact by charge polarization mechanism leading to elongation in average H-H bond length indicating physisorption. Sorption energy decreases gradually from ≈0.4 to 0.20 eV on H2 loading. Molecular dynamics simulations and computed sorption energy range indicate the high reversibility of H2 in the MGF-Li8 framework with the hydrogen storage capacity of 6.4 wt %. The calculated thermodynamic practical hydrogen storage at room temperature makes the Li-decorated MGF system a promising hydrogen storage material.
Energy Technology Data Exchange (ETDEWEB)
Peng, Degao; Yang, Yang; Zhang, Peng [Department of Chemistry, Duke University, Durham, North Carolina 27708 (United States); Yang, Weitao, E-mail: weitao.yang@duke.edu [Department of Chemistry and Department of Physics, Duke University, Durham, North Carolina 27708 (United States)
2014-12-07
In this article, we develop systematically second random phase approximations (RPA) and Tamm-Dancoff approximations (TDA) of particle-hole and particle-particle channels for calculating molecular excitation energies. The second particle-hole RPA/TDA can capture double excitations missed by the particle-hole RPA/TDA and time-dependent density-functional theory (TDDFT), while the second particle-particle RPA/TDA recovers non-highest-occupied-molecular-orbital excitations missed by the particle-particle RPA/TDA. With proper orbital restrictions, these restricted second RPAs and TDAs have a formal scaling of only O(N{sup 4}). The restricted versions of second RPAs and TDAs are tested with various small molecules to show some positive results. Data suggest that the restricted second particle-hole TDA (r2ph-TDA) has the best overall performance with a correlation coefficient similar to TDDFT, but with a larger negative bias. The negative bias of the r2ph-TDA may be induced by the unaccounted ground state correlation energy to be investigated further. Overall, the r2ph-TDA is recommended to study systems with both single and some low-lying double excitations with a moderate accuracy. Some expressions on excited state property evaluations, such as 〈S{sup ^2}〉 are also developed and tested.
Peng, Degao; Yang, Yang; Zhang, Peng; Yang, Weitao
2014-12-01
In this article, we develop systematically second random phase approximations (RPA) and Tamm-Dancoff approximations (TDA) of particle-hole and particle-particle channels for calculating molecular excitation energies. The second particle-hole RPA/TDA can capture double excitations missed by the particle-hole RPA/TDA and time-dependent density-functional theory (TDDFT), while the second particle-particle RPA/TDA recovers non-highest-occupied-molecular-orbital excitations missed by the particle-particle RPA/TDA. With proper orbital restrictions, these restricted second RPAs and TDAs have a formal scaling of only O(N4). The restricted versions of second RPAs and TDAs are tested with various small molecules to show some positive results. Data suggest that the restricted second particle-hole TDA (r2ph-TDA) has the best overall performance with a correlation coefficient similar to TDDFT, but with a larger negative bias. The negative bias of the r2ph-TDA may be induced by the unaccounted ground state correlation energy to be investigated further. Overall, the r2ph-TDA is recommended to study systems with both single and some low-lying double excitations with a moderate accuracy. Some expressions on excited state property evaluations, such as < hat{S}2rangle are also developed and tested.
Energy Technology Data Exchange (ETDEWEB)
Spiesser, Ph.
1996-05-01
A user interface has been developed for geometrical and thermal data acquisition, in order to allow calculations of heat diffusion in certain types of electronic circuits such as power hybrids and compact electronic modules, using computerized simulations. Data management, structure and organization, the data acquisition interface program, and variables and sources, are described
Liebscher, C H; Freysoldt, C; Dennenwaldt, T; Harzer, T P; Dehm, G
2017-07-01
Metastable Cu-Cr alloy thin films with nominal thickness of 300nm and composition of Cu67Cr33 (at%) are obtained by co-evaporation using molecular beam epitaxy. The microstructure, chemical phase separation and electronic structure are investigated by transmission electron microscopy (TEM). The thin film adopts the body-centered cubic crystal structure and consists of columnar grains with ~50nm diameter. Aberration-corrected scanning TEM in combination with energy dispersive X-ray spectroscopy confirms compositional fluctuations within the grains. Cu- and Cr-rich domains with composition of Cu85Cr15 (at%) and Cu42Cr58 (at%) and domain size of 1-5nm are observed. The alignment of the interface between the Cu- and Cr-rich domains shows a preference for {110}-type habit plane. The electronic structure of the Cu-Cr thin films is investigated by electron energy loss spectroscopy (EELS) and is contrasted to an fcc-Cu reference sample. The experimental EEL spectra are compared to spectra computed by density functional theory. The main differences between bcc-and fcc-Cu are related to differences in van Hove singularities in the electron density of states. In Cu-Cr solid solutions with bcc crystal structure a single peak after the L3-edge, corresponding to a van Hove singularity at the N-point of the first Brillouin zone is observed. Spectra computed for pure bcc-Cu and random Cu-Cr solid solutions with 10at% Cr confirm the experimental observations. The calculated spectrum for a perfect Cu50Cr50 (at%) random structure shows a shift in the van Hove singularity towards higher energy by developing a Cu-Cr d-band that lies between the delocalized d-bands of Cu and Cr. Copyright © 2016 Elsevier B.V. All rights reserved.
Gomes, André Severo Pereira; Visscher, Lucas; Bolvin, Hélène; Saue, Trond; Knecht, Stefan; Fleig, Timo; Eliav, Ephraim
2010-08-14
The triiodide ion I(3)(-) exhibits a complex photodissociation behavior, the dynamics of which are not yet fully understood. As a first step toward determining the full potential energy surfaces of this species for subsequent simulations of its dissociation processes, we investigate the performance of different electronic structure methods [time-dependent density functional theory, complete active space perturbation theory to second order (CASPT2), Fock-space coupled cluster and multireference configuration interaction] in describing the ground and excited states of the triiodide ion along the symmetrical dissociation path. All methods apart from CASPT2 include scalar relativity and spin-orbit coupling in the orbital optimization, providing useful benchmark data for the more common two-step approaches in which spin-orbit coupling is introduced in the configuration interaction. Time-dependent density functional theory with the statistical averaging of model orbital potential functional is off the mark for this system. Another choice of functional may improve performance with respect to vertical excitation energies and spectroscopic constants, but all functionals are likely to face instability problems away from the equilibrium region. The Fock-space coupled cluster method was shown to perform clearly best in regions not too far from equilibrium but is plagued by convergence problems toward the dissociation limit due to intruder states. CASPT2 shows good performance at significantly lower computational cost, but is quite sensitive to symmetry breaking. We furthermore observe spikes in the CASPT2 potential curves away from equilibrium, signaling intruder state problems that we were unable to curb through the use of level shifts. Multireference configuration interaction is, in principle, a viable option, but its computational cost in the present case prohibits use other than for benchmarking purposes.
Gomes, André Severo Pereira; Visscher, Lucas; Bolvin, Hélène; Saue, Trond; Knecht, Stefan; Fleig, Timo; Eliav, Ephraim
2010-08-01
The triiodide ion I3- exhibits a complex photodissociation behavior, the dynamics of which are not yet fully understood. As a first step toward determining the full potential energy surfaces of this species for subsequent simulations of its dissociation processes, we investigate the performance of different electronic structure methods [time-dependent density functional theory, complete active space perturbation theory to second order (CASPT2), Fock-space coupled cluster and multireference configuration interaction] in describing the ground and excited states of the triiodide ion along the symmetrical dissociation path. All methods apart from CASPT2 include scalar relativity and spin-orbit coupling in the orbital optimization, providing useful benchmark data for the more common two-step approaches in which spin-orbit coupling is introduced in the configuration interaction. Time-dependent density functional theory with the statistical averaging of model orbital potential functional is off the mark for this system. Another choice of functional may improve performance with respect to vertical excitation energies and spectroscopic constants, but all functionals are likely to face instability problems away from the equilibrium region. The Fock-space coupled cluster method was shown to perform clearly best in regions not too far from equilibrium but is plagued by convergence problems toward the dissociation limit due to intruder states. CASPT2 shows good performance at significantly lower computational cost, but is quite sensitive to symmetry breaking. We furthermore observe spikes in the CASPT2 potential curves away from equilibrium, signaling intruder state problems that we were unable to curb through the use of level shifts. Multireference configuration interaction is, in principle, a viable option, but its computational cost in the present case prohibits use other than for benchmarking purposes.
Energy Technology Data Exchange (ETDEWEB)
Kostko, Oleg; Bravaya, Ksenia; Krylov, Anna; Ahmed, Musahid
2009-12-14
We report a combined theoretical and experimental study of ionization of cytosine monomers and dimers. Gas-phase molecules are generated by thermal vaporization of cytosine followed by expansion of the vapor in a continuous supersonic jet seeded in Ar. The resulting species are investigated by single photon ionization with tunable vacuum-ultraviolet (VUV) synchrotron radiation and mass analyzed using reflectron mass spectrometry. Energy onsets for the measured photoionization efficiency (PIE) spectra are 8.60+-0.05 eV and 7.6+-0.1 eV for the monomer and the dimer, respectively, and provide an estimate for the adiabatic ionization energies (AIE). The first AIE and the ten lowest vertical ionization energies (VIEs) for selected isomers of cytosine dimer computed using equation-of-motion coupled-cluster (EOM-IP-CCSD) method are reported. The comparison of the computed VIEs with the derivative of the PIE spectra, suggests that multiple isomers of the cytosine dimer are present in the molecular beam. The calculations reveal that the large red shift (0.7 eV) of the first IE of the lowest-energy cytosine dimer is due to strong inter-fragment electrostatic interactions, i.e., the hole localized on one of the fragments is stabilized by the dipole moment of the other. A sharp rise in the CH+ signal at 9.20+-0.05 eV is ascribed to the formation of protonated cytosine by dissociation of the ionized dimers. The dominant role of this channel is supported by the computed energy thresholds for the CH+ appearance and the barrierless or nearly barrierless ionization-induced proton transfer observed for five isomers of the dimer.
Brorsen, Kurt R; Yang, Yang; Hammes-Schiffer, Sharon
2017-08-03
Nuclear quantum effects such as zero point energy play a critical role in computational chemistry and often are included as energetic corrections following geometry optimizations. The nuclear-electronic orbital (NEO) multicomponent density functional theory (DFT) method treats select nuclei, typically protons, quantum mechanically on the same level as the electrons. Electron-proton correlation is highly significant, and inadequate treatments lead to highly overlocalized nuclear densities. A recently developed electron-proton correlation functional, epc17, has been shown to provide accurate nuclear densities for molecular systems. Herein, the NEO-DFT/epc17 method is used to compute the proton affinities for a set of molecules and to examine the role of nuclear quantum effects on the equilibrium geometry of FHF-. The agreement of the computed results with experimental and benchmark values demonstrates the promise of this approach for including nuclear quantum effects in calculations of proton affinities, pKa's, optimized geometries, and reaction paths.
DEFF Research Database (Denmark)
Rosenberg, Martin; Ottosson, Henrik; Kilså, Kristine
2010-01-01
Aromaticity has importance for proton and hydride affinities in the singlet ground state (S(0)) of annulenyl anions and cations so that, e.g., cyclopentadiene is an acidic hydrocarbon. For the lowest pipi* excited triplet state (T(1)), Baird's rule concludes that annulenes with 4n pi......-electrons are aromatic and those with 4n+2 pi-electrons are antiaromatic, opposite to Huckel's rule for aromaticity in S(0). Our hypothesis is now that the relative magnitudes of proton and hydride affinities of annulenyl anions and cations reverts systematically as one goes from S(0) to T(1) as a result of the opposite...... electron counting rules for aromaticity in the two states. Using quantum chemical calculations at the G3(MP2)//(U)B3LYP/6-311+G(d,p) level we have examined the validity of this hypothesis for eight proton and eight hydride addition reactions of anions and cations, respectively, of annulenyl...
Jiang, He; Chen, Changshui
2015-04-23
Most material properties can be traced to electronic structures. Black silicon produced from SF6 or sulfur powder via irradiation with femtosecond laser pulses displays decreased infrared absorption after annealing, with almost no corresponding change in visible light absorption. The high-intensity laser pulses destroy the original crystal structure, and the doping element changes the material performance. In this work, the structural and electronic properties of several sulfur-doped silicon systems are investigated using first principle calculations. Depending on the sulfur concentration (level of doping) and the behavior of the sulfur atoms in the silicon lattice, different states or an absence of states are exhibited, compared with the undoped system. Moreover, the visible-infrared light absorption intensities are structure specific. The results of our theoretical calculations show that the conversion efficiency of sulfur-doped silicon solar cells depends on the sulfur concentrations. Additionally, two types of defect configurations exhibit light absorption characteristics that differ from the other configurations. These two structures produce a rapid increase in the theoretical photoelectric conversion efficiency in the range of the specific chemical potential studied. By controlling the positions of the atomic sulfur and the sulfur concentration in the preparation process, an efficient photovoltaic (PV) material may be obtainable.
Faizan, Mohd; Alam, Mohammad Jane; Ahmad, Shabbir
2017-11-01
In the present investigation, spectroscopic techniques (FTIR, FT-Raman and UV-Vis) and quantum chemical calculations are employed for exploring vibrational and electronic spectra of sulindac compound. The calculations are performed on most stable conformer of the sulindac molecule using density functional theory (DFT). Anharmonic corrections are made to frequencies using vibrational second-order perturbation theory (VPT2). The effect of intermolecular interactions on the vibrational dynamics has been analyzed using dimeric structure of sulindac molecule. Hirshfeld surface analysis and 2D fingerprint plots are utilized to investigate the nature of interaction present in the crystal system. To account for electronic spectra in different solvents, an integral equation formalism of polarizable continuum model (IEFPCM) at TD-DFT/B3LYP/6-31G(d,p) level of theory has been employed. An excellent agreement between the theoretical and experimental data over the entire spectral region is observed. In addition, natural bond orbital (NBO) analysis, frontier molecular orbitals, nonlinear optical properties (NLO) and molecular electrostatic potential (MEP) analysis are also reported.
Gibbons, John P.; Antolak, John A.; Followill, David S.; Huq, M. Saiful; Klein, Eric E.; Lam, Kwok L.; Palta, Jatinder R.; Roback, Donald M.; Reid, Mark; Khan, Faiz M.
2014-01-01
A protocol is presented for the calculation of monitor units (MU) for photon and electron beams, delivered with and without beam modifiers, for constant source-surface distance (SSD) and source-axis distance (SAD) setups. This protocol was written by Task Group 71 of the Therapy Physics Committee of the American Association of Physicists in Medicine (AAPM) and has been formally approved by the AAPM for clinical use. The protocol defines the nomenclature for the dosimetric quantities used in these calculations, along with instructions for their determination and measurement. Calculations are made using the dose per MU under normalization conditions, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} }{}$D_0^\\prime $\\end{document}D0′, that is determined for each user's photon and electron beams. For electron beams, the depth of normalization is taken to be the depth of maximum dose along the central axis for the same field incident on a water phantom at the same SSD, where \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} }{}$D_0^\\prime $\\end{document}D0′ = 1 cGy/MU. For photon beams, this task group recommends that a normalization depth of 10 cm be selected, where an energy-dependent \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} }{}$D_0^\\prime $\\end{document}D0′ ≤ 1 cGy/MU is required. This recommendation differs from the more common approach of a normalization depth of dm, with
Habib, B; Poumarede, B; Tola, F; Barthe, J
2010-01-01
The aim of the present study is to demonstrate the potential of accelerated dose calculations, using the fast Monte Carlo (MC) code referred to as PENFAST, rather than the conventional MC code PENELOPE, without losing accuracy in the computed dose. For this purpose, experimental measurements of dose distributions in homogeneous and inhomogeneous phantoms were compared with simulated results using both PENELOPE and PENFAST. The simulations and experiments were performed using a Saturne 43 linac operated at 12 MV (photons), and at 18 MeV (electrons). Pre-calculated phase space files (PSFs) were used as input data to both the PENELOPE and PENFAST dose simulations. Since depth-dose and dose profile comparisons between simulations and measurements in water were found to be in good agreement (within +/-1% to 1 mm), the PSF calculation is considered to have been validated. In addition, measured dose distributions were compared to simulated results in a set of clinically relevant, inhomogeneous phantoms, consisting of lung and bone heterogeneities in a water tank. In general, the PENFAST results agree to within a 1% to 1 mm difference with those produced by PENELOPE, and to within a 2% to 2 mm difference with measured values. Our study thus provides a pre-clinical validation of the PENFAST code. It also demonstrates that PENFAST provides accurate results for both photon and electron beams, equivalent to those obtained with PENELOPE. CPU time comparisons between both MC codes show that PENFAST is generally about 9-21 times faster than PENELOPE. Copyright 2009 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
D'Ordine, Robert L; Pawlak, Jaroslaw; Bahnson, Brian J; Anderson, Vernon E
2002-02-26
When alpha,beta-unsaturated substrates bind to the active site of enoyl-CoA hydratase, large spectral changes can be observed [D'Ordine, R. L., et al. (1994) Biochemistry 33, 12635-12643]. The differences in the isotropic magnetic shieldings of the free and active site-bound forms of the carbonyl, alpha-, and beta-carbons of the substrates, hexadienoyl-CoA, cinnamoyl-CoA, and (N,N-dimethyl-p-amino)cinnamoyl-CoA have been experimentally determined. The carbonyl and beta-carbons are all deshielded, while the alpha-carbons show increased shielding. These chemical shift perturbations are interpreted to suggest that the pi-electrons of the enoyl thiolester are polarized when bound at the active site. Using the crystal structure of (N,N-dimethyl-p-amino)cinnamoyl-CoA bound at the enzyme active site, the shielding tensors were calculated at three different levels of theory, up to a density functional theory model that included all of the contiguous active site residues. These calculations successfully reproduced the observed spectral changes and permitted the electronic polarization of the substrate to be quantified as an electron density difference map. The calculated electron density difference confirms the loss of electrons at the electrophilic beta-carbon and carbonyl carbon, while a slight increase in electron density at the alpha-carbon where proton donation occurs during the hydration reaction and a larger increase in electron density at the carbonyl oxygen are predicted. The energy required to polarize the electrons to the observed extent was calculated to be 3.2 kcal/mol. The force that provides the requisite energy for the polarization is the interaction of the electric field generated by the protein at the enzyme active site with the polarizable electrons of the substrate. Because the induced electronic polarization is along the predicted reaction pathway, the extent of substrate activation by the induced electronic strain is catalytically relevant.
Rafique, Muhammad; Shuai, Yong; Xu, Meng; Zhang, Guohua; Guo, Yanming
2017-09-01
Graphene-based magnetic materials have revealed great potential for developing high-performance electronic units at sub-nanometer such as spintronic data storage devices. However, a significant ferromagnetism behavior and ample band gap in the electronic structure of graphene is required before it can be used for actual engineering applications. Based on first-principles calculations, here we demonstrate the structural, electronic and magnetic behaviors of 5d transition metal (TM) atom-substituted nitrogenized monolayer graphene. We find that, during TMN(3)4 cluster-substitution, tight bonding occurs between impurity atoms and graphene with significant binding energies. Charge transfer occurs from graphene layer to the TMN(3)4 clusters. Interestingly, PtN3, TaN4 and ReN4 cluster-doped graphene structures exhibit dilute magnetic semiconductor behavior with 1.00 μB, 1.04 μB and 1.05 μB magnetic moments, respectively. While, OsN4 and PtN4 cluster-doped structures display nonmagnetic direct band gap semiconductor behavior. Remaining, TMN(3)4 cluster-doped graphene complexes exhibit half metal properties. Detailed analysis of density of states (DOS) plots indicate that d orbitals of TM atoms should be responsible for arising magnetic moments in graphene. Given results pave a new route for potential applications of dilute magnetic semiconductors and half-metals in spintronic devices by employing TMN(3)4 cluster-doped graphene complexes.
Energy Technology Data Exchange (ETDEWEB)
Li Hongnian; Ni Jingfu; Wang Peng; Meng Liang; Wang Xiaobo [Department of Physics, Zhejiang University, Hangzhou 310027 (China); Yang Hua; Liu Ziyang [Department of Chemistry, Zhejiang University, Hangzhou 310027 (China); Wang Xiaoxiong [College of Science, Nanjing University of Science and Technology, Nanjing 210094 (China); Kurash, Ibrahim; Qian Haijie; Wang Jiaou [Laboratory of Synchrotron Radiation, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039 (China)], E-mail: Phylihn@public.zju.edu.cn
2009-07-01
We have measured the photoemission spectra of a C{sub 84} film (isomer mixture) with synchrotron radiation. The valence band exhibits abundant spectral features from the Fermi level to {approx}18 eV binding energy. The relative intensity between the lowest binding energy feature (labeled as A) and the next lowest binding energy feature (labeled as B) oscillates distinctly within the experimental photon energy region from 21.0 to 63.0 eV. The energy levels and density of states (DOS) are calculated for the D{sub 2d}(23)- C{sub 84} and four D{sub 2} symmetric (D{sub 2}(1), D{sub 2}(5), D{sub 2}(21) and D{sub 2}(22)) C{sub 84} isomers to help us to understand the electronic structure. The experimental features and the theoretical DOS peaks have one-to-one correspondence. The number of electrons occupying the states of feature A is 12 or 13.3, depending on the different kinds of isomer mixtures. The electron occupation of feature B is 18.67 e. With the spherical symmetric approximation, features A and B can be characterized with angular momenta of 6 and 5, respectively. The angular momentum difference is the reason for the photoelectron intensity oscillations.
Peng, Yen-Chun; Chen, Chieh-Cheng; Wu, Hsuan-Chung; Lu, Jong-Hong
2015-01-01
This study adopted first-principles calculations to evaluate the effects of intrinsic defects on the electronic structure and optical properties of Boron-doped ZnO (BZO). Four types of defect were considered: non-defective (BZn), Zn vacancies (VZn), O vacancies (VO), and interstitial Zn (Zni). Calculations of formation energy illustrate that O-rich conditions tend to induce VZn, while O-poor conditions tend to induce VO and Zni. With respect to electric properties, VZn defects in BZO decrease carrier concentration as well as mobility, which consequently decreases the conductivity of BZO. The existence of VO or Zni defects in BZO leads to n-type conductive characteristics and increases the optical band gap. The existence of Zni defects in BZO also increases the effective mass, which decreases the mobility and conductivity of BZO. As for the optical properties, the introduction of VZn to BZO leads to an increase in transmittance in the visible light region, but a decrease in the UV region. The introduction of intrinsic VO and Zni defects to BZO leads to a significant decrease in transmittance in the visible as well as UV regions. The calculated results were also compared with experimental data from the literature.
Energy Technology Data Exchange (ETDEWEB)
Yi, Jun; Zhao, Zong-Yan, E-mail: zzy@kmust.edu.cn
2014-12-15
Europium-doped luminescent heavy metal bismuth oxychloride has been investigated by first-principles calculation, and the crystal structure, electronic structure, and optical properties of pure BiOCl and Eu-doped BiOCl have been examined and compared. Based on the calculated results, the luminescence properties and mechanism of Eu-doped BiOCl has been discussed. Owing to the unique layered structure, BiOCl host could produce enough separated electron–hole pairs, under UV-light excitation. Furthermore, because the energy levels ({sup 5}D{sub 0}) of Eu{sup 3+} is matched with the energy bands (the bottom of conduction band) of BiOCl, the energy transport and charge transfer from host to luminescence center can be efficiently carried out. Thus, the photoluminescence of Eu{sup 3+} could be enhanced in the matrix of BiOCl. These findings are helpful to understand previously published experimental results, and to improve novel luminescence materials. - Highlights: • Eu doping effects in BiOCl were systematically studied by first-principles calculations. • Eu doping causes very gentle lattice distortion, and induces crystal expansion. • BiOCl host could produce enough separated electron–hole pairs, under UV-light excitation. • Energy transport and charge transfer from BiOCl to Eu{sup 3+} can be efficiently carried out.
Bluteau, M M; Badnell, N R
2015-01-01
With construction of ITER progressing and existing tokamaks carrying out ITER-relevant experiments, accurate fundamental and derived atomic data for numerous ionization stages of tungsten (W) is required to assess the potential effect of this species upon fusion plasmas. The results of fully relativistic, partially radiation damped, Dirac $R$-matrix electron-impact excitation calculations for the W$^{44+}$ ion are presented. These calculations use a configuration interaction and close-coupling expansion that opens-up the 3d-subshell, which does not appear to have been considered before in a collision calculation. As a result, it is possible to investigate the arrays, [3d$^{10}$4s$^2-$3d$^9$4s$^2$4f] and [3d$^{10}$4s$^2-$3d$^9$4s4p4d], which are predicted to contain transitions of diagnostic importance for the soft x-ray region. Our $R$-matrix collision data are compared with previous $R$-matrix results by Ballance and Griffin as well as our own relativistically corrected, Breit-Pauli distorted wave and plane-...
Energy Technology Data Exchange (ETDEWEB)
Du, Jincheng [University of North Texas; Devanathan, Ram [Pacific Northwest National Laboratory (PNNL); Corrales, L Rene [University of Arizona; Weber, William J [ORNL
2012-01-01
First principle periodic density functional theory (DFT) calculations have been performed to understand the electronic structure, chemical bonding, phase transition, and physical properties of the zircon (in the chemical composition of ZrSiO4) and its high pressure phase reidite. Temperature effect on phase transition and thermal-mechanical properties such as heat capacity and bulk modulus have been studied by combining the equation of states obtained from DFT calculations with the quasi-harmonic Debye model to take into account the entropy contribution to free energy. Local density approximation (LDA) and generalized gradient approximation (GGA) DFT functionals have been systematically compared in predicting the structure and property of this material. It is found that the LDA functional provides a better description of the equilibrium structure and bulk modulus, while GGA predicts a transition pressure closer to experimental values. Both functionals correctly predict the relative stability of the two phases, with GGA giving slightly larger energy differences. The calculated band structures show that both zircon and reidite have indirect bandgaps and the reidite phase has a narrower bandgap than the zircon phase. The atomic charges determined using the Bader method show that bonding in reidite has a stronger covalent character.
Strenalyuk, Tatyana; Samdal, Svein; Volden, Hans Vidar
2008-10-09
The molecular structure of phthalocyaninatotin(II), Sn(II)Pc, is determined by density functional theory (DFT/B3LYP) calculations using various basis sets and gas-phase electron diffraction (GED). The quantum chemical calculations show that Sn(II)Pc has C4V symmetry, and this symmetry is consistent with the structure obtained by GED at 427 degrees C. GED locates the Sn atom at h(Sn) ) 112.8(48) pm above the plane defined by the four isoindole N atoms, and a N-Sn bond length of 226.0(10) pm is obtained. Calculation at the B3LYP/ccpVTZ/cc-pVTZ-PP(Sn) level of theory gives h(Sn) ) 114.2 pm and a N-Sn bond length of 229.4 pm. The phthalocyanine (Pc) macrocycle has a slightly nonplanar structure. Generally, the GED results are in good agreement with the X-ray structures and with the computed structure; however, the comparability between these three methods has been questioned. The N-Sn bond lengths determined by GED and X-ray are significantly shorter than those from the B3LYP predictions. Similar trends have been found for C-Sn bonds for conjugated organometallic tin compounds. Computed vibrational frequencies give five low frequencies in the range of 18-54 cm-1, which indicates a flexible molecule.
Samdal, S; Volden, H V; Ferro, V R; García de la Vega, J M; Gonzalez-Rodríguez, D; Torres, T
2007-05-24
The molecular structure of the chloro-dodecafluorosubphthalocyaninato boron(III) (F-SubPc) was determined with use of Gas Electron Diffraction (GED) and high-level quantum chemical calculations. The present results show that the F-SubPc molecule has a cone-shaped configuration, isoindole units are not planar, and the pyrrole ring has an envelope conformation. The structure parameters in the gas phase are determined. Some structural details can be observed such as the dihedral angle about the bond connecting the pyrrole ring and the benzene ring being ca. 174 degrees . High-level theoretical calculations with several extended basis sets for this molecule have been carried out. The calculations are in very good agreement with experimental methods: X-ray and GED. Nevertheless, some disagreements particularly related to the B-Cl bond distance found in GED are discussed. Vibrational frequencies were computed obtaining eight values below 100 cm-1 and three bending potentials were examined. They suggest that this molecule is very flexible.
DEFF Research Database (Denmark)
Høholdt, Tom; Beelen, Peter; Ghorpade, Sudhir Ramakant
2010-01-01
We consider a new class of linear codes, called affine Grassmann codes. These can be viewed as a variant of generalized Reed-Muller codes and are closely related to Grassmann codes.We determine the length, dimension, and the minimum distance of any affine Grassmann code. Moreover, we show...
Albert, Julian; Hader, Kilian; Engel, Volker
2017-12-28
It is commonly assumed that the time-dependent electron flux calculated within the Born-Oppenheimer (BO) approximation vanishes. This is not necessarily true if the flux is directly determined from the continuity equation obeyed by the electron density. This finding is illustrated for a one-dimensional model of coupled electronic-nuclear dynamics. There, the BO flux is in perfect agreement with the one calculated from a solution of the time-dependent Schrödinger equation for the coupled motion. A reflection principle is derived where the nuclear BO flux is mapped onto the electronic flux.
Calculation of electron emission from a tantalum foil irradiated by 100-kV and 50-kV x-rays
Energy Technology Data Exchange (ETDEWEB)
Berger, M.J.
1998-03-01
Two Monte Carlo programs, XITRAN and XMTRAN, were developed for calculating the emission of electrons from high-Z foils irradiated with x rays. XITRAN follows all individual elastic collisions of electrons with atoms, whereas XMTRAN uses the condensed-random-walk model. Both codes take into account photo-electrons, fluorescence radiation, and Auger electrons. Comparisons are made with an experiment by Dolan at Sandia Laboratories involving the backward and forward emission of electrons from a tantalum foil irradiated by 100-kV and 50-kV x-ray beams. There is good agreement between results from the XITRAN and XMTRAN codes. There emitted per incident x-ray photon, and in regard to the angular distribution of the emerging electrons. In regard to the electron energy spectra, there is fair agreement down to a spectral energy of 20 keV, whereas below 20 keV the calculated spectra lie considerably below the measurements.
Energy Technology Data Exchange (ETDEWEB)
Ritley, K.A. [Univ. of Illinois, Urbana, IL (United States); Ghosh, V.J.; Lynn, K.G.; McKewown, M.; Welch, D.O. [Brookhaven National Lab., Upton, NY (United States)
1997-10-20
SPRITE (Simulation of Particle Reemission, Implantation and Transmission--Extensible) is a Fortran computer program designed to model the transport of a stream of energetic particles as they scatter through a solid or multilayer. SPRITE is intended to be a user-friendly and easily-extensible engine for performing basic transport calculations, and SPRITE incorporates such physics as is required to simulate the transport process, but specifically omits the details of the scattering mechanisms. PSPRITE is a Fortran computer program, built around the SPRITE transport engine and incorporating physical information necessary for modeling the implantation and thermalization of a stream of positrons or electrons with a solid. This document is intended to be the primary source of information and the only operations manual for SPRITE and the POS-SPRITE family of programs. This information includes the mode of operation of SPRITE, the format of the required and optional file types, as well as information about the output and results of the calculation. Information about installing and running these programs on a variety of computer systems will not be addressed in this report. Such information is rapidly expanding as these programs are adapted to run on different platforms, and thus the user can expect such information to be contained with the source code distribution set. Detailed information about the calculations of the structure of the POS-SPRITE programs are provided in this report, but detailed benchmark comparisons between the output of these calculations and experimental data are an active topic of research, and they refer the reader to the published literature for this information.
Ab initio electronic structure calculations for Mn linear chains deposited on CuN/Cu(001) surfaces
Energy Technology Data Exchange (ETDEWEB)
Barral, Maria Andrea [Departamento de Fisica ' Juan Jose Giambiagi' , Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, 1428 Buenos Aires (Argentina)]. E-mail: barral@df.uba.ar; Weht, Ruben [Departamento de Fisica, Comision Nacional de Energia Atomica, Avenida del Libertador 8250, 1429 Buenos Aires (Argentina); Lozano, Gustavo [Departamento de Fisica ' Juan Jose Giambiagi' , Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, 1428 Buenos Aires (Argentina); Maria Llois, Ana [Departamento de Fisica ' Juan Jose Giambiagi' , Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, 1428 Buenos Aires (Argentina); Departamento de Fisica, Comision Nacional de Energia Atomica, Avenida del Libertador 8250, 1429 Buenos Aires (Argentina)
2007-09-01
In a recent experiment, scanning tunneling microscopy has been used to obtain a direct probe of the magnetic interaction in linear manganese chains arranged by atomic manipulation on thin insulating copper nitride islands grown on Cu(001). The local spin excitation spectra of these chains have been measured with inelastic electron tunneling spectroscopy. Analyzing the spectroscopic results with a Heisenberg Hamiltonian the interatomic coupling strength within the chains has been obtained. It has been found that the coupling strength depends on the deposition sites of the Mn atoms on the islands. In this contribution, we perform ab initio calculations for different arrangements of infinite Mn chains on CuN in order to understand the influence of the environment on the value of the magnetic interactions.
Role of anion doping on electronic structure and magnetism of GdN by first principles calculations
Zhang, Xuejing
2014-01-01
We have investigated the electronic structure and magnetism of anion doped GdN1-yXy (X = B, C, O, F, P, S and As) systems by first-principles calculations based on density functional theory. GdN 1-yXy systems doped by O, C, F, P, and S atoms are more stable than those doped by B and As atoms because of relatively high binding energies. The anion doping and the N defect states modify the density of states at the Fermi level, resulting in a decrease in spin polarization and a slight increase in the magnetic moment at the Gd and N sites. © 2014 The Royal Society of Chemistry.
Energy Technology Data Exchange (ETDEWEB)
Bouzidi, Chaker, E-mail: bouzidtc@yahoo.fr [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National des Recherches en Sciences des Matériaux, BP No.73, 8027 Soliman (Tunisia); Horchani-Naifer, Karima; Khadraoui, Zied [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National des Recherches en Sciences des Matériaux, BP No.73, 8027 Soliman (Tunisia); Elhouichet, Habib [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National des Recherches en Sciences des Matériaux, BP No.73, 8027 Soliman (Tunisia); Département de Physique, Faculté des Sciences de Tunis, Université de Tunis-ElManar ElManar, 2092 Tunis (Tunisia); Ferid, Mokhtar [Laboratoire de Physico-chimie des Matériaux Minéraux et leurs Applications, Centre National des Recherches en Sciences des Matériaux, BP No.73, 8027 Soliman (Tunisia)
2016-09-15
The electronic and optical properties of calcium molybdate (CaMoO{sub 4}) have been determined by X-ray diffraction, spectroscopic measurements and calculations of energy-band structures, density of states, and optical response functions by density functional theory. The chemical bonding analysis indicates that Mo–O bonds exhibit more covalent character than the Ca–O bond. The linear photon-energy-dependent dielectric functions, conductivity, refractive index, reflectivity and extinction coefficients were investigated and analyzed. The results are in agreement with previous theoretical works and the experimental data. Reflectivity spectra revealed that the CaMoO{sub 4} promises as good coating materials in the energy region of 9.3–11.6 eV with reflectivity larger than 75%.
Energy Technology Data Exchange (ETDEWEB)
Imai, Y. [National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 5, Higashi 1-1 Tsukuba, Ibaraki 305-8565 (Japan); Watanabe, A. [National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 5, Higashi 1-1 Tsukuba, Ibaraki 305-8565 (Japan)
2006-06-29
The electronic structures of platinum group elements (Ru, Os, Rh, Ir, Pd, and Pt) silicides have been calculated. Ir{sub 3}Si{sub 5} is a semiconductor with the direct gap of 1.14 eV. Among monosilicides, RuSi and OsSi with the FeSi-type structure are semiconductors with the gap values of 0.21 and 0.41 eV but RhSi, IrSi, PdSi, and PtSi with the MnP-type structure are metals. No semiconducting compounds can be found in other platinum group elements silicides other than known Ru{sub 2}Si{sub 3}, Os{sub 2}Si{sub 3}, and OsSi{sub 2}.
Shi, Qinqin
2016-03-21
An efficient iodination reaction of electron-deficient heterocycles is described. The reaction utilizes KOtBu as an initiator and likely proceeds by a radical anion propagation mechanism. This new methodology is particularly effective for functionalization of building blocks for electron transport materials. Its utility is demonstrated with the synthesis of a new perylenediimide-thiazole non-fullerene acceptor capable of delivering a power conversion efficiency of 4.5% in a bulk-heterojunction organic solar cell. © 2016 American Chemical Society.
Affine and Projective Geometry
Bennett, M K
1995-01-01
An important new perspective on AFFINE AND PROJECTIVE GEOMETRY. This innovative book treats math majors and math education students to a fresh look at affine and projective geometry from algebraic, synthetic, and lattice theoretic points of view. Affine and Projective Geometry comes complete with ninety illustrations, and numerous examples and exercises, covering material for two semesters of upper-level undergraduate mathematics. The first part of the book deals with the correlation between synthetic geometry and linear algebra. In the second part, geometry is used to introduce lattice theory
Energy Technology Data Exchange (ETDEWEB)
Noll, Daniel [Goethe Univ., Frankfurt (Germany); Stancari, Giulio [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
2015-11-17
An electron lens is planned for the Fermilab Integrable Optics Test Accelerator as a nonlinear element for integrable dynamics, as an electron cooler, and as an electron trap to study space-charge compensation in rings. We present the main design principles and constraints for nonlinear integrable optics. A magnetic configuration of the solenoids and of the toroidal section is laid out. Singleparticle tracking is used to optimize the electron path. Electron beam dynamics at high intensity is calculated with a particle-in-cell code to estimate current limits, profile distortions, and the effects on the circulating beam. In the conclusions, we summarize the main findings and list directions for further work.
Electronic structure of ceramic CrSi2 and WSi2: Compton spectroscopy and ab-initio calculations
Bhamu, K. C.; Sahariya, Jagrati; Ahuja, B. L.
2013-05-01
We report electron momentum densities of stable phases of transition metal disilicides CrSi2 (C40 hexagonal) and WSi2 (C11b body centered tetragonal) using a high energy 137Cs Compton spectrometer. To support the experimental investigations, we have computed theoretical Compton profiles, energy bands and density of states of both the isoelectronic compounds using density functional theory within linear combination of atomic orbitals. Theoretical calculations for the energy bands and density of states are performed for both the hexagonal and tetragonal phases of these silicides. In the tetragonal phase, both the silicides show metallic behavior. The hexagonal CrSi2 shows an energy gap (0.28 eV) between the valence band maximum at the L point and the conduction band minimum at the M point of the Brillouin zone, whereas the hexagonal WSi2 shows a semimetallic character. We have also scaled the experimental and theoretical profiles of the stable phases (hexagonal for CrSi2 and tetragonal for WSi2) on equal-valence-electron-density, which show more covalent character of WSi2 than that of CrSi2. The nature of bonding is in accordance with a present Mulliken's population analysis.
Partovi-Azar, P.; Panahian Jand, S.; Kaghazchi, P.
2018-01-01
Edge termination of graphene nanoribbons is a key factor in determination of their physical and chemical properties. Here, we focus on nitrogen-terminated zigzag graphene nanoribbons resembling polyacrylonitrile-based carbon nanofibers (CNFs) which are widely studied in energy research. In particular, we investigate magnetic, electronic, and transport properties of these CNFs as functions of their widths using density-functional theory calculations together with the nonequilibrium Green's function method. We report on metallic behavior of all the CNFs considered in this study and demonstrate that the narrow CNFs show finite magnetic moments. The spin-polarized electronic states in these fibers exhibit similar spin configurations on both edges and result in spin-dependent transport channels in the narrow CNFs. We show that the partially filled nitrogen dangling-bond bands are mainly responsible for the ferromagnetic spin ordering in the narrow samples. However, the magnetic moment becomes vanishingly small in the case of wide CNFs where the dangling-bond bands fall below the Fermi level and graphenelike transport properties arising from the π orbitals are recovered. The magnetic properties of the CNFs as well as their stability have also been discussed in the presence of water molecules and the hexagonal boron nitride substrate.
Vinodkumar, Minaxi; Limbachiya, Chetan; Antony, Bobby; Joshipura, K. N.
2007-08-01
In this paper we report comprehensive calculations of total elastic (Qel), total ionization (Qion) and total (complete) cross sections (QT) for the impact of electrons on inert gases (He, Ne, Ar, Kr and Xe) at energies from about threshold to 2000 eV. We have employed the spherical complex optical potential (SCOP) formalism to evaluate Qel and QT and used the complex spherical potential-ionization contribution (CSP-ic) method to derive Qion. The dependence of QT on polarizability and incident energy is presented for these targets through an analytical formula. Mutual comparison of various cross sections is provided to show their relative contribution to the total cross sections QT. Comparison of QT for all these targets is carried out to present a general theoretical picture of collision processes. The present calculations also provide information, hitherto sparse, on the excitation processes of these atomic targets. These results are compared with available experimental and other theoretical data and overall good agreement is observed.
Energy Technology Data Exchange (ETDEWEB)
Segala, Maximiliano, E-mail: max-segala@uergs.edu.b [Universidade Estadual do Rio Grande do Sul, Rua Oscar Matzembacher 475, 96760-000 Tapes, RS (Brazil); Chong, Delano P. [Department of Chemistry, 2036 Main Mall, University of British Columbia, Vancouver, B.C., V6T 1Z1 (Canada)
2010-12-15
Research highlights: {yields} CEBEs(P1s) with AAD = 0.20 eV. {yields} CEBEs(S1s) with AAD = 0.22 eV. {yields} AAD changes slightly with the apparent orbital hybridization of the atom. {yields} Allometric approximation performs well for the CEBEs(1s) for P and S. -- Abstract: In this paper, 1s ionization energies for P- and S-containing molecules were calculated using energy-difference method by DFT. Using observed core-electron binding energies (CEBEs) as reference, we found that the Becke00x(xc) exchange-correlation functional (E{sub xc}) is the best choice for CEBEs(P1s), with an average absolute deviation (AAD) of 0.20 eV, and that the best choice for CEBEs(S1s) is E{sub xc} = BmTau1, with an average absolute deviation (AAD) of 0.22 eV. However, the best single functional for calculation of both P and S is E{sub xc} = VS98, resulting in the weighted AAD of 0.43 eV. Our results are also showing that the quality of AAD changes slightly with the apparent orbital hybridization of the atom.
Krapf, Sebastian; Koslowski, Thorsten; Steinbrecher, Thomas
2010-08-28
DNA Photolyases are light sensitive oxidoreductases present in many organisms that participate in the repair of photodamaged DNA. They are capable of electron transfer between a bound cofactor and a chain of tryptophan amino acid residues. Due to their unique mechanism and important function, photolyases have been subject to intense study in recent times, with both experimental and computational efforts. In this work, we present a novel application of classical molecular dynamics based free energy calculations, combined with quantum mechanical computations, to biomolecular charge transfer. Our approach allows for the determination of all reaction parameters in Marcus' theory of charge transport. We were able to calculate the free energy profile for the movement of a positive charge along protein sidechains involved in the biomolecule's function as well as charge-transfer rates that are in good agreement with experimental results. Our approach to simulate charge-transfer reactions explicitly includes the influence of protein flexibility and solvent dynamics on charge-transfer energetics. As applied here to a biomolecular system of considerable scientific interest, we believe the method to be easily adaptable to the study of charge-transfer phenomena in biochemistry and other fields.
Zaharo, Aflah; Purqon, Acep
2017-07-01
The calculation of the structure and electronic properties of Rare Earth (RE) at the wurtzite Gallium Nitride (GaN) based on DFT has completed. GGA approximation used for exchange correlation and Ultra soft pseudo potential too. The stability structure of GaN is seen that difference lattice parameter 11% lower than another calculation and experiment result. It is shown the stability structure GaN have direct band gap energy on Gamma point hexagonal lattice Brillouin zone. The width Eg is 2.6 eV. When one atom Ga is substituted with one atom RE, the bond length is change 12 % longest. An in good agreement with theoretical doping RE concentration increases, the edge of energy level shifted towards to make the band gap narrow which is allow the optical transitions and help to improve the optical performance of GaN. The RE doped GaN is potentially applicable for various color of LED with lower energy consumption and potentially energy saving application
Measuring an antibody affinity distribution molecule by molecule
Energy Technology Data Exchange (ETDEWEB)
Bradbury, Andrew M [Los Alamos National Laboratory; Werner, James H [Los Alamos National Laboratory; Temirov, Jamshid [INVITROGEN
2008-01-01
Single molecule fluorescence mIcroscopy was used to observe the binding and unbinding of hapten decorated quantum dots with individual surface immobilized antibodies. The fluorescence time history from an individual antibody site can be used to calculate its binding affinity. While quantum dot blinking occurs during these measurements, we describe a simple empirical method to correct the apparent/observed affinity to account for the blinking contribution. The combination of many single molecule affinity measurements from different antibodies yields not only the average affinity, it directly measures the full shape and character of the surface affinity distribution function.
Robust Affine Invariant Descriptors
Directory of Open Access Journals (Sweden)
Jianwei Yang
2011-01-01
Full Text Available An approach is developed for the extraction of affine invariant descriptors by cutting object into slices. Gray values associated with every pixel in each slice are summed up to construct affine invariant descriptors. As a result, these descriptors are very robust to additive noise. In order to establish slices of correspondence between an object and its affine transformed version, general contour (GC of the object is constructed by performing projection along lines with different polar angles. Consequently, affine in-variant division curves are derived. A slice is formed by points fall in the region enclosed by two adjacent division curves. To test and evaluate the proposed method, several experiments have been conducted. Experimental results show that the proposed method is very robust to noise.
Akbari, Ahmad; Naseri, Mosayeb; Jalilian, Jaafar
2018-01-01
In this paper, based on full potential density functional theory calculations, the electronic and optical properties of aluminium and gallium phosphide (AlP and GaP) graphene-like structures are investigated under different biaxial compressive and tensile strain loads. One of the fascinating properties of these new monolayers is their high stretch-ability and high mechanosensitivity of their electronic and optical features. The electronic calculations display that the energy gap of materials versus the exerted strain can be estimated by a second order polynomial equation. Furthermore, the optical calculations indicate that the electronic and optical gap of AlP and GaP monolayers can be tuned by biaxial strain loads.
Derrickson, J. H.; Dake, S.; Dong, B. L.; Eby, P. B.; Fountain, W. F.; Fuki, M.; Gregory, J. C.; Hayashi, T.; Iyono, A.; King, D. T.
1989-01-01
Recently, new calculations were made of the direct Coulomb pair cross section that rely less in arbitrary parameters. More accurate calculations of the cross section down to low pair energies were made. New measurements of the total direct electron pair yield, and the energy and angular distribution of the electron pairs in emulsion were made for O-16 at 60 and 200 GeV/amu at S-32 at 200 GeV/amu which give satisfactory agreement with the new calculations. These calculations and measurements are presented along with previous accelerator measurements made of this effect during the last 40 years. The microscope scanning criteria used to identify the direct electron pairs is described. Prospects for application of the pair method to cosmic ray energy measurements in the region 10 (exp 13) to 10 (exp 15) eV/amu are discussed.
Bousis, Christos; Emfietzoglou, Dimitris; Nikjoo, Hooshang
2012-12-01
To calculate the absorbed fraction (AF) of low energy electrons in small tissue-equivalent spherical volumes by Monte Carlo (MC) track structure simulation and assess the influence of phase (liquid water versus density-scaled water vapor) and of the continuous-slowing-down approximation (CSDA) used in semi-analytic calculations. An event-by-event MC code simulating the transport of electrons in both the vapor and liquid phase of water using appropriate electron-water interaction cross sections was used to quantify the energy deposition of low-energy electrons in spherical volumes. Semi-analytic calculations within the CSDA using a convolution integral of the Howell range-energy expressions are also presented for comparison. The AF for spherical volumes of radii from 10-1000 nm are presented for monoenergetic electrons over the energy range 100-10,000 eV and the two Auger-emitting radionuclides (125)I and (123)I. The MC calculated AF for the liquid phase are found to be smaller than those of the (density scaled) gas phase by up to 10-20% for the monoenergetic electrons and 10% for the two Auger-emitters. Differences between the liquid-phase MC results and the semi-analytic CSDA calculations are up to ∼ 55% for the monoenergetic electrons and up to ∼ 35% for the two Auger-emitters. Condensed-phase effects in the inelastic interaction of low-energy electrons with water have a noticeable but relatively small impact on the AF for the energy range and target sizes examined. Depending on the electron energies, the semi-analytic approach may lead to sizeable errors for target sizes with linear dimensions below 1 micron.
Chi, C.-C.; Hsiao, C.-H.; Skoropata, E.; van Lierop, J.; Ouyang, Chuenhou Hao
2015-05-01
Significant efforts towards understanding bi-magnetic core-shell nanoparticles are underway currently as they provide a pathway towards properties unavailable with single-phased systems. Recently, we have demonstrated that the magnetism of γ-Fe2O3/CoO core-shell nanoparticles, in particular, at high temperatures, originates essentially from an interfacial doped iron-oxide layer that is formed by the migration of Co2+ from the CoO shell into the surface layers of the γ-Fe2O3 core [Skoropata et al., Phys. Rev. B 89, 024410 (2014)]. To examine directly the nature of the intermixed layer, we have used high-resolution transmission electron microscopy (HRTEM) and first-principles calculations to examine the impact of the core-shell intermixing at the atomic level. By analyzing the HRTEM images and energy dispersive spectra, the level and nature of intermixing was confirmed, mainly as doping of Co into the octahedral site vacancies of γ-Fe2O3. The average Co doping depths for different processing temperatures (150 °C and 235 °C) were 0.56 nm and 0.78 nm (determined to within 5% through simulation), respectively, establishing that the amount of core-shell intermixing can be altered purposefully with an appropriate change in synthesis conditions. Through first-principles calculations, we find that the intermixing phase of γ-Fe2O3 with Co doping is ferromagnetic, with even higher magnetization as compared to that of pure γ-Fe2O3. In addition, we show that Co doping into different octahedral sites can cause different magnetizations. This was reflected in a change in overall nanoparticle magnetization, where we observed a 25% reduction in magnetization for the 235 °C versus the 150 °C sample, despite a thicker intermixed layer.
Deng, Yunfeng; Sun, Bin; He, Yinghui; Quinn, Jesse; Guo, Chang; Li, Yuning
2016-03-01
Three thiophene-S,S-dioxidized indophenine (IDTO) isomers, 3 a (E,E,E), 3 b (Z,E,E), and 3 c (Z,E,Z), were synthesized by oxidation of an indophenine compound. 3 b and 3 c could be converted into the most-stable 3 a by heating at 110 °C. An IDTO-containing conjugated polymer, PIDTOTT, was prepared using 3 a as a comonomer through a Stille coupling reaction, and it possesses a narrow band gap and low energy levels. In organic field effect transistors (OFETs), PIDTOTT exhibited unipolar n-type semiconductor characteristics with unexpectedly high electron mobility (up to 0.14 cm(2) V(-1) s(-1)), despite its rather disordered chain packing. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Watanabe, Shinta; Sawada, Yuki; Nakaya, Masato; Yoshino, Masahito; Nagasaki, Takanori; Kameyama, Tatsuya; Torimoto, Tsukasa; Inaba, Yusuke; Takahashi, Hideharu; Takeshita, Kenji; Onoe, Jun
2016-06-01
We have investigated the electronic structures and optical properties of Fe, Co, and Ni ferrocyanide nanoparticles using first-principles relativistic many-electron calculations. The overall features of the theoretical absorption spectra for Fe, Ni, and Co ferrocyanides calculated using a first-principles many-electron method well reproduced the experimental one. The origins of the experimental absorption spectra were clarified by performing a configuration analysis based on the many-electron wave functions. For Fe ferrocyanide, the experimental absorption peaks originated from not only the charge-transfer transitions from Fe2+ to Fe3+ but also the 3d-3d intra-transitions of Fe3+ ions. In addition, the spin crossover transition of Fe3+ predicted by the many-electron calculations was about 0.24 eV. For Co ferrocyanide, the experimental absorption peaks were mainly attributed to the 3d-3d intra-transitions of Fe2+ ions. In contrast to the Fe and Co ferrocyanides, Ni ferrocyanide showed that the absorption peaks originated from the 3d-3d intra-transitions of Ni3+ ions in a low-energy region, while from both the 3d-3d intra-transitions of Fe2+ ions and the charge-transfer transitions from Fe2+ to Ni3+ in a high-energy region. These results were quite different from those of density-functional theory (DFT) calculations. The discrepancy between the results of DFT calculations and those of many-electron calculations suggested that the intra- and inter-atomic transitions of transition metal ions are significantly affected by the many-body effects of strongly correlated 3d electrons.
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Watanabe, Shinta, E-mail: s-watanabe@nucl.nagoya-u.ac.jp, E-mail: j-onoe@nucl.nagoya-u.ac.jp; Sawada, Yuki; Nakaya, Masato; Yoshino, Masahito; Nagasaki, Takanori; Onoe, Jun, E-mail: s-watanabe@nucl.nagoya-u.ac.jp, E-mail: j-onoe@nucl.nagoya-u.ac.jp [Department of Materials, Physics and Energy Engineering, Graduated School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Kameyama, Tatsuya; Torimoto, Tsukasa [Department of Crystalline Materials Science, Graduated School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Inaba, Yusuke; Takahashi, Hideharu; Takeshita, Kenji [Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1-N1-16 O-okayama, Meguro-ku, Tokyo 152-8550 (Japan)
2016-06-21
We have investigated the electronic structures and optical properties of Fe, Co, and Ni ferrocyanide nanoparticles using first-principles relativistic many-electron calculations. The overall features of the theoretical absorption spectra for Fe, Ni, and Co ferrocyanides calculated using a first-principles many-electron method well reproduced the experimental one. The origins of the experimental absorption spectra were clarified by performing a configuration analysis based on the many-electron wave functions. For Fe ferrocyanide, the experimental absorption peaks originated from not only the charge-transfer transitions from Fe{sup 2+} to Fe{sup 3+} but also the 3d-3d intra-transitions of Fe{sup 3+} ions. In addition, the spin crossover transition of Fe{sup 3+} predicted by the many-electron calculations was about 0.24 eV. For Co ferrocyanide, the experimental absorption peaks were mainly attributed to the 3d-3d intra-transitions of Fe{sup 2+} ions. In contrast to the Fe and Co ferrocyanides, Ni ferrocyanide showed that the absorption peaks originated from the 3d-3d intra-transitions of Ni{sup 3+} ions in a low-energy region, while from both the 3d-3d intra-transitions of Fe{sup 2+} ions and the charge-transfer transitions from Fe{sup 2+} to Ni{sup 3+} in a high-energy region. These results were quite different from those of density-functional theory (DFT) calculations. The discrepancy between the results of DFT calculations and those of many-electron calculations suggested that the intra- and inter-atomic transitions of transition metal ions are significantly affected by the many-body effects of strongly correlated 3d electrons.
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Rached, H., E-mail: habib_rached@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences Exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès, 22000 (Algeria); Département de Physique, Faculté des Sciences Exactes et Informatique, Université Hassiba BenBouali de Chlef, Chlef, 02000 (Algeria); Bendaoudia, S. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences Exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès, 22000 (Algeria); Rached, D., E-mail: rachdj@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences Exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès, 22000 (Algeria)
2017-06-01
The main goal of the present work is to obtain report on the magnetic phase stability, mechanical, electronic and optical properties of double perovskite oxides Pb{sub 2}FeMO{sub 6} (M = Mo, Re and W) by employing the ab-initio plane-wave method, based on the density functional theory (DFT). The exchange-correlation (XC) energy of electrons was treated using the Perdew–Burke–Ernzerhof parametrization. The ground-state electronic properties for different magnetic configurations were calculated. The formation enthalpies has been evaluated in order to determinate the stability of our compounds. The independent elastic constants and the related mechanical properties are investigated. The electronic structure calculation reveal the half-metallic ferrimagnets (FiM-HM) for all investigated compounds. The optical constants as the dielectric function, refractive index, optical reflectivity and absorption coefficient were calculated and discussed in detail. Therefore, our compounds are identified as potential candidates for spintronic applications and high performance electronic devices. - Highlights: • Based on the DFT calculation, the Pb{sub 2}FeMO{sub 6} (M = Mo, Re and W) compounds have been investigated. • The ground-state properties are predicted. • The mechanical properties reveals that these compounds are stable against any elastic deformations. • The electronic structures reveals the half-metallic ferrimagnets (FiM-HM) for all investigated compounds.
Andrews, Lester; Wang, Xuefeng; Gong, Yu; Kushto, Gary P; Vlaisavljevich, Bess; Gagliardi, Laura
2014-07-17
Reactions of laser-ablated U atoms with N2 molecules upon codeposition in excess argon or neon at 4 K gave intense NUN and weak UN absorptions. Annealing produced progressions of new absorptions for the UN2(N2)1,2,3,4,5 and UN(N2)1,2,3,4,5,6 complexes. The neon-to-argon matrix shift decreases with increasing NN ligation and therefore the number of noble gas atoms left in the primary coordination sphere around the NUN molecule. Small matrix shifts are observed when the secondary coordination layers around the primary UN2(N2)1,2,3,4,5 and UN(N2)1,2,3,4,5,6 complexes are changed from neon-to-argon to nitrogen. Electronic structure, energy, and frequency calculations provide support for the identification of these complexes and the characterization of the N≡U≡N and U≡N core molecules as terminal uranium nitrides. Codeposition of U with pure nitrogen produced the saturated U(NN)7 complex, which UV irradiation converted to the NUN(NN)5 complex with slightly lower frequencies than found in solid argon.
Drablia, S.; Boukhris, N.; Boulechfar, R.; Meradji, H.; Ghemid, S.; Ahmed, R.; Omran, S. Bin; El Haj Hassan, F.; Khenata, R.
2017-10-01
The alkaline earth metal chalcogenides are being intensively investigated because of their advanced technological applications, for example in photoluminescent devices. In this study, the structural, electronic, thermodynamic and thermal properties of the BaSe1-x Te x alloys at alloying composition x = 0, 0.25, 0.50, 0.75 and 1 are investigated. The full potential linearized augmented plane wave plus local orbital method designed within the density functional theory was used to perform the total energy calculations. In this research work the effect of the composition on the results of the parameters and bulk modulus as well as on the band gap energy is analyzed. From our results, we found a deviation of the obtained results for the lattice constants from Vegard’s law as well as a deviation of the value of the bulk modulus from the linear concentration dependence. We also carried out a microscopic analysis of the origin of the band gap energy bowing parameter. Furthermore, the thermodynamic stability of the considered alloys was explored through the measurement of the miscibility critical temperature. The quasi-harmonic Debye model, as implemented in the Gibbs code, was used to predict the thermal properties of the BaSe1-x Te x alloys, and these investigations comprise our first theoretical predictions concerning the BaSe1-x Te x alloys.
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Pershina, V. [Gesellschaft fuer Schwerionenforschung, Darmstadt (Germany)
2005-07-01
Thermodynamics of adsorption of gaseous species on the surface of a gas chromatography column is considered using the knowledge of the electronic structure of the adsorbate. Relevant equations based on a model of mobile adsorption are offered to predict the adsorption temperature, T{sub ads}, of a heavy-element (or its compound) with respect to T{sub ads} of its lighter homolog (or the same type of compound). A case of adsorption of OsO{sub 4} and HsO{sub 4} on an inert (quartz or silicon nitride) surface of a chromatography column is taken, as an example. The influence of various properties of the adsorbate, such as molecular weight and size, on T{sub ads} is analyzed to show that those factors should not be ignored in intentionally accurate predictions of T{sub ads}. A comparison of the desorption constants of OsO{sub 4} and HsO{sub 4} obtained with the use of the calculated spectroscopic properties shows that HsO{sub 4} should be significantly more volatile than OsO{sub 4}, mainly due to the entropy factor. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Olsson, Paer
2004-04-01
The efficiency of fast neutron reactors, such as for fusion, breeding and transmutation, depend strongly on the neutron radiation resistance of the materials used in the reactors. The binary Fe-Cr alloy, which has many attractive properties in this regard, is the base for the best steels of today which are, however, still not up to the required standards. Therefore, substantial effort has been devoted to finding new materials that can cope with the demands better. Experimental studies must be complemented with extensive theoretical modelling in order to understand the effects that different alloying elements has on the resistance properties of materials. To this end, the first steps of multi-scale modelling has been taken, starting out with ab initio calculations of the electronic structure of the complete concentration range range of the disordered binary Fe-C alloy. The mixing enthalpy of Fe-Cr has been quantitatively predicted and has, together with data from literature, been used in order to fit two sets of interatomic potentials for the purpose of simulating defect evolution with molecular dynamics and kinetic Monte-Carlo codes. These dedicated Fe-Cr alloy potentials are new and represent important additions to the pure element potentials that can be found in literature.
Antibody-based affinity cryo-EM grid.
Yu, Guimei; Li, Kunpeng; Jiang, Wen
2016-05-01
The Affinity Grid technique combines sample purification and cryo-Electron Microscopy (cryo-EM) grid preparation into a single step. Several types of affinity surfaces, including functionalized lipids monolayers, streptavidin 2D crystals, and covalently functionalized carbon surfaces have been reported. More recently, we presented a new affinity cryo-EM approach, cryo-SPIEM, which applies the traditional Solid Phase Immune Electron Microscopy (SPIEM) technique to cryo-EM. This approach significantly simplifies the preparation of affinity grids and directly works with native macromolecular complexes without need of target modifications. With wide availability of high affinity and high specificity antibodies, the antibody-based affinity grid would enable cryo-EM studies of the native samples directly from cell cultures, targets of low abundance, and unstable or short-lived intermediate states. Copyright © 2016 Elsevier Inc. All rights reserved.
Rosenberg, Martin; Ottosson, Henrik; Kilså, Kristine
2010-04-02
Aromaticity has importance for proton and hydride affinities in the singlet ground state (S(0)) of annulenyl anions and cations so that, e.g., cyclopentadiene is an acidic hydrocarbon. For the lowest pipi* excited triplet state (T(1)), Baird's rule concludes that annulenes with 4n pi-electrons are aromatic and those with 4n+2 pi-electrons are antiaromatic, opposite to Huckel's rule for aromaticity in S(0). Our hypothesis is now that the relative magnitudes of proton and hydride affinities of annulenyl anions and cations reverts systematically as one goes from S(0) to T(1) as a result of the opposite electron counting rules for aromaticity in the two states. Using quantum chemical calculations at the G3(MP2)//(U)B3LYP/6-311+G(d,p) level we have examined the validity of this hypothesis for eight proton and eight hydride addition reactions of anions and cations, respectively, of annulenyl and benzannulenyl type. We categorize the (4n+2)pi-electron systems in S(0) and the 4npi-electron systems in T(1) to be of A-character and 4npi-electron systems in S(0) and (4n+2)pi-electron systems in T(1) to be of AA-character (A, aromatic; AA, anti/nonaromatic). The average proton affinities of anions of A- and AA-characters in S(0) are 1447 and 1521 kJ/mol, respectively, and in T(1) they are 1365 and 1493 kJ/mol. The average hydride affinities of A- and AA-character cations in S(0) are 826 and 996 kJ/mol, and in T(1) they are 790 and 879 kJ/mol, respectively. Thus, the calculated proton and hydride affinities are in general lower for anions and cations of A-character than for those of AA-character, in good support of our hypothesis. The findings could likely be applied in synthetic organic photochemistry and other areas where excited state acid-base chemistry plays a role.
Azri, Hemza; Demir, Durmuş
2018-02-01
Induced gravity, metrical gravity in which gravitational constant arises from vacuum expectation value of a heavy scalar, is known to suffer from Jordan frame vs Einstein frame ambiguity, especially in inflationary dynamics. Induced gravity in affine geometry, as we show here, leads to an emergent metric and gravity scale, with no Einstein-Jordan ambiguity. While gravity is induced by the vacuum expectation value of the scalar field, nonzero vacuum energy facilitates generation of the metric. Our analysis shows that induced gravity results in a relatively large tensor-to-scalar ratio in both metrical and affine gravity setups. However, the fact remains that the induced affine gravity provides an ambiguity-free framework.
Golebiowski, Jérôme; Lamare, Véronique; Martins-Costa, Marilia T. C.; Millot, Claude; Ruiz-López, Manuel F.
2001-10-01
We report molecular dynamics simulations of calixarene-crown-ether complexes with alkali cations in water using hybrid quantum mechanics/molecular mechanics (QM/MM) potentials. The approach allows us, for the first time in this kind of systems, to make a detailed discussion on the role of electronic polarization. Such an effect had been omitted in previous studies of calixarene-alkali cation complexes, although it is known to be important in many host-guest systems. The macrocycle, calix[4]arene-bis-crown6 (BC6), is treated at the semiempirical AM1 level whereas solvent water molecules are treated using the TIP3P model. The alkali metal cations (Na + and Cs +) are described as classical point charges with a set of Lennard-Jones parameters developed in this work. The interaction energy is analysed in terms of strain, electrostatic, polarization and van der Waals contributions. The polarization component is shown to be substantial and may represent 20% of the total electrostatic energy. We show that instantaneous fluctuation of the net atomic charge on O atoms and aromatic rings are quite large. The structural results predicted by the AM1/TIP3P model are shown to agree reasonably well with X-ray data. Comparison with previous MM simulations using effective pairwise additive potentials is made. Some differences found in the case of the BC6/Na + system, namely for the solvation number, are discussed.
Chari, Vyjayanthi; Pressley, Andrew
1991-12-01
We classify the finite-dimensional irreducible representations of the quantum affine algebraU_q (hat sl_2 ) in terms of highest weights (this result has a straightforward generalization for arbitrary quantum affine algebras). We also give an explicit construction of all such representations by means of an evaluation homomorphismU_q (hat sl_2 ) to U_q (sl_2 ), first introduced by M. Jimbo. This is used to compute the trigonometric R-matrices associated to finite-dimensional representations ofU_q (hat sl_2 ).
Energy Technology Data Exchange (ETDEWEB)
Mohr, H. [Department of Physics, University of Surrey, Guildford, Surrey, GU2 5XH (United Kingdom)
1996-12-01
Electron beam induced current (EBIC) microscopy is a very powerful technique for revealing the electrical activity of defects in semiconductors. Gettering of impurities at defects has been observed previously after certain sample heat treatments, which resulted in altered contrast patterns and line scan profiles. Getter effects have been included in a numerical or analytical contrast simulation which employ the Monte Carlo method for generating the carrier distribution. We compare the findings with an observed white contrast at misfit dislocations in EBIC micrographs. {copyright} {ital 1996 American Institute of Physics.}
Fan Affinity Laws from a Collision Model
Bhattacharjee, Shayak
2012-01-01
The performance of a fan is usually estimated using hydrodynamical considerations. The calculations are long and involved and the results are expressed in terms of three affinity laws. In this paper we use kinetic theory to attack this problem. A hard sphere collision model is used, and subsequently a correction to account for the flow behaviour…
You, Shihu; Gou, Chengjun; Wu, Zhangwen; Hou, Qing
2015-07-01
As an electron beam is incident on a uniform water phantom in the presence of a lateral magnetic field, the depth-dose distribution of the electron beam changes significantly and forms the well-known 'Bragg peak', with a depth-dose distribution similar to that of heavy ions. This phenomenon has pioneered a new field in the clinical application of electron beams. For such clinical applications, evaluating the penetration depth of electron beams quickly and accurately is the critical problem. This paper describes a model for calculating the penetration depth of an electron beam rapidly and correctly in a water phantom under the influence of a magnetic field. The model was used to calculate the penetration depths under different conditions: the energies of electron beams of 6, 8, 12 and 15 MeV and the magnetic induction intensities of 0.75, 1.0, 1.5, 2.0 and 3.0 T. In addition, the calculation results were compared with the results of a Monte Carlo simulation. The comparison results indicate that the difference between the two calculation methods was less than 0.5 cm. Moreover, the computing time of the calculation model was less than a second. The semi-analytical model proposed in the present study enables the penetration depth of the electron beam in the presence of a magnetic field to be obtained with a computational efficiency higher than that of the Monte Carlo approach; thus, the proposed model has high potential for application. Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
Dixon, David A; Grant, Daniel J; Christe, Karl O; Peterson, Kirk A
2008-06-16
Atomization energies at 0 K and heats of formation at 0 and 298 K are predicted for IF, IF2-, IF2+, IF3, IF4-, IF4+, IF5, IF6-, IF6+, IF7, IF8-, BrF6-, and ClF6- from coupled cluster theory [CCSD(T)] calculations with effective-core potential correlation-consistent basis sets for I. In order to achieve near chemical accuracy (+/-1 kcal/mol), three corrections were added to the complete basis set binding energies based on frozen-core coupled-cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, and a correction for first-order atomic spin-orbit effects. Vibrational zero-point energies were computed at the coupled-cluster level of theory except for IF6-, IF7, and IF8-. The calculated heats of formation for the neutral and ionic IFn fluorides were used to predict fluoride affinities. It is shown that high-level calculations are required to predict correctly the steric activity of the free-valence electron pair on the central atoms in IF6- (C3v), BrF6- (Oh), and ClF6- (Oh ). The vibrational spectrum of IF8- was reanalyzed, and complete mode descriptions for square-antiprismatic XF8 species of D4d symmetry are given.
Pogosov, V. V.; Reva, V. I.
2017-09-01
In terms of the model of stable jellium, self-consistent calculations of spatial distributions of electrons and potentials, as well as of energies of dissociation, cohesion, vacancy formation, electron attachment, and ionization potentials of solid clusters of Mg N , Li N (with N ≤ 254 ) and of clusters containing a vacancy ( N ≥ 12) have been performed. The contribution of a monovacancy to the energy of the cluster and size dependences of its characteristics and of asymptotics have been discussed. Calculations have been performed using a SKIT-3 cluster at Glushkov Institute of Cybernetics, National Academy of Sciences, Ukraine (Rpeak = 7.4 Tflops).
National Oceanic and Atmospheric Administration, Department of Commerce — Ionospheric Total Electron Content (TEC) is the total number of electrons in a column of unit cross section extending from the transmitter to the receiver. TEC is...
Energy Technology Data Exchange (ETDEWEB)
Zaluzec, Nestor J.
2014-05-22
Closed form analytical equations used to calculate the collection solid angle of six common geometries of solid-state X-ray detectors in scanning and scanning/transmission analytical electron microscopy are presented. Using these formulae one can make realistic comparisons of the merits of the different detector geometries in modern electron column instruments. This work updates earlier formulations and adds new detector configurations.
Noble-Eddy, Robert; Masters, Sarah L. (nee Hinchley); Rankin, David W. H.; Wann, Derek A.; Khater, Brahim; Guillemin, Jean-Claude
2008-01-01
The molecular structures of methylphosphine (CH3PH2) and methylphosphine-borane (CH3PH2·BH3) have been determined from gas-phase electron diffraction data and rotational constants, employing the SARACEN method. The experimental geometric parameters generally showed a good agreement with those obtained using ab initio calculations and previous microwave spectroscopy studies. In order to assess the accuracy of the calculated structures a range of ab initio methods were used, including the CCSD(...
Schrager, D.F.
2006-01-01
We propose a new model for stochastic mortality. The model is based on the literature on affine term structure models. It satisfies three important requirements for application in practice: analytical tractibility, clear interpretation of the factors and compatibility with financial option pricing
Minguzzi, E.
2017-03-01
We investigate spacetimes whose light cones could be anisotropic. We prove the equivalence of the structures: (a) Lorentz-Finsler manifold for which the mean Cartan torsion vanishes, (b) Lorentz-Finsler manifold for which the indicatrix (observer space) at each point is a convex hyperbolic affine sphere centered on the zero section, and (c) pair given by a spacetime volume and a sharp convex cone distribution. The equivalence suggests to describe (affine sphere) spacetimes with this structure, so that no algebraic-metrical concept enters the definition. As a result, this work shows how the metric features of spacetime emerge from elementary concepts such as measure and order. Non-relativistic spacetimes are obtained replacing proper spheres with improper spheres, so the distinction does not call for group theoretical elements. In physical terms, in affine sphere spacetimes the light cone distribution and the spacetime measure determine the motion of massive and massless particles (hence the dispersion relation). Furthermore, it is shown that, more generally, for Lorentz-Finsler theories non-differentiable at the cone, the lightlike geodesics and the transport of the particle momentum over them are well defined, though the curve parametrization could be undefined. Causality theory is also well behaved. Several results for affine sphere spacetimes are presented. Some results in Finsler geometry, for instance in the characterization of Randers spaces, are also included.
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Ciftci, Yasemin Oe. [Gazi University Teknikokullar, Department of Physics, Faculty of Sciences, Ankara (Turkey); Evecen, Meryem; Aldirmaz, Emine [Amasya University, Department of Physics, Faculty of Arts and Sciences, Amasya (Turkey)
2017-01-15
First-principles calculations for the structural, elastic, electronic and vibrational properties of BeGeAs{sub 2} with chalcopyrite structure have been reported in the frame work of the density functional theory. The calculated ground state properties are in good agreement with the available data. By considering the electronic band structure and electronic density of states calculation, it is found that this compound is a semiconductor which confirmed the previous work. Single-crystal elastic constants and related properties such as Young's modulus, Poisson ratio, shear modulus and bulk modulus have been predicted using the stress-finite strain technique. It can be seen from the calculated elastic constants that this compound is mechanically stable in the chalcopyrite structure. Pressure dependences of elastic constants and band gap are also reported. Finally, the phonon dispersion curves and total and partial density of states were calculated and discussed. The calculated phonon frequencies BeGeAs{sub 2} are positive, indicating the dynamical stability of the studied compound. (orig.)
Moruzzi, VL
1995-01-01
This is a handbook of calculated electronic properties of elements and of 3d/3d and 4d/4d ordered alloys. The book derives the ground-state or equilibrium properties of the metallic elements in both bcc and fcc structures, and of existing and nonexisting ordered binary transition-metal alloys in CsCl, CuAu, and Cu 3 Au structures by the analysis of binding curves, or total energy vs. volume curves, calculated from first-principles augmented-spherical-wave methods. The calculated properties, energy bands along symmetry lines in the respective Brillouin zones, and the total and I-decomposed dens
Bates, Kevin R.; Daniels, Andrew D.; Scuseria, Gustavo E.
1998-01-01
We report a comparison of two linear-scaling methods which avoid the diagonalization bottleneck of traditional electronic structure algorithms. The Chebyshev expansion method (CEM) is implemented for carbon tight-binding calculations of large systems and its memory and timing requirements compared to those of our previously implemented conjugate gradient density matrix search (CG-DMS). Benchmark calculations are carried out on icosahedral fullerenes from C60 to C8640 and the linear scaling memory and CPU requirements of the CEM demonstrated. We show that the CPU requisites of the CEM and CG-DMS are similar for calculations with comparable accuracy.
Liljequist, David
2012-01-01
Backscattering of very low energy electrons in thin layers of amorphous ice is known to provide experimental data for the elastic and inelastic cross sections and indicates values to be expected in liquid water. The extraction of cross sections was based on a transport analysis consistent with Monte Carlo simulation of electron trajectories. However, at electron energies below 20 eV, quantum coherence effects may be important and trajectory-based methods may be in significant error. This possibility is here investigated by calculating quantum multiple elastic scattering of electrons in a simple model of a very small, thin foil of amorphous ice. The average quantum multiple elastic scattering of electrons is calculated for a large number of simulated foils, using a point-scatterer model for the water molecule and taking inelastic absorption into account. The calculation is compared with a corresponding trajectory simulation. The difference between average quantum scattering and trajectory simulation at energies below about 20 eV is large, in particular in the forward scattering direction, and is found to be almost entirely due to coherence effects associated with the short-range order in the amorphous ice. For electrons backscattered at the experimental detection angle (45° relative to the surface normal) the difference is however small except at electron energies below about 10 eV. Although coherence effects are in general found to be strong, the mean free path values derived by trajectory-based analysis may actually be in fair agreement with the result of an analysis based on quantum scattering, at least for electron energies larger than about 10 eV.
Fang, C.M.; Groot, R.A. de; Wiegers, G.A.; Haas, C.
1996-01-01
In order to understand the electronic structure of the incommensurate misfit layer compound (SnS)1.20TiS2 we carried out an ab initio band structure calculation in the supercell approximation. The band structure is compared with that of the components 1T-TiS2 and hypothetical SnS with a similar
Fang, CM; deGroot, RA; Wiegers, GA; Haas, C
1996-01-01
In order to understand the electronic structure of the incommensurate misfit layer compound (SnS)(1.20)TiS2 we carried out an ab initio band structure calculation in the supercell approximation. The band structure is compared with that of the components 1T-TiS2 and hypothetical SnS with a similar
Sasse, A.G.B.M.; Wormeester, Herbert; van der Hoef, Martin Anton; Keim, Enrico G.; van Silfhout, Arend
1989-01-01
The line shape of the Si-L2,3 VV Auger spectrum is to a first approximation equal to the sum of the convolution products of the partial local density of states (pLDOS), each weighted by the two electron Auger matrix elements and the escape depth. Semiempirical quantum chemical cluster calculations
Energy Technology Data Exchange (ETDEWEB)
Michalski, R. [Inst. of Physics, Pedagocial Univ., Cracow (Poland); Radwanski, R.J. [Center for Solid State Physics, Cracow (Poland)
2005-07-01
The aim of this paper is to demonstrate the effectiveness of the calculation method, which takes into consideration the electrostatic ligands field as well as the the magnetic interactions. Our calculations method based on crystal field (CEF) together with the Zeeman effect in one Hamiltonian and allows calculating many of the temperature dependencies of the magnetic and electronic properties of the rare earth compounds. The result of the calculations shows the accuracy of the approach even for the intermetallic compounds. The obtained results for calculations of the compounds of the family in RERu{sub 2}Si{sub 2} (RE - rare-earth element) are fully confirmed the experimental data such as: the easy magnetic direction of all the analyzed compounds, the thermal dependencies of magnetic properties; in particular the giant magnetocrystalline anisotropy of PrRu{sub 2}S{sub 2} with the calculated anisotropy field B{sub A}>400T, in-plain anisotropy of ErRu{sub 2}Si{sub 2}, the cause of difficulty in magnetic ordering of compounds TmRu{sub 2}Si{sub 2} and YbRu{sub 2}Si{sub 2} as well as effects and dependencies not foreseen before. In this paper we have put together the elementary calculated magnetic properties for the chosen compounds of RERu{sub 2}Si{sub 2} in the paramagnetic region. All Calculations are on the basis of the calculating computer package BIREC 1.5{sup 1}. (orig.)
Hardiansyah, D.; Male, S.; Haryanto, F.
2014-09-01
Prism is a non-commercial Radiotherapy Treatment Planning System (RTPS) develop by Ira J. Kalet from Washington University. Inhomogeneity factor is included in Prism TPS dose calculation. The aim of this study is to investigate the sensitivity of dose calculation on Prism using Monte Carlo simulation. Phase space source from head linear accelerator (LINAC) for Monte Carlo simulation is implemented. To achieve this aim, Prism dose calculation is compared with EGSnrc Monte Carlo simulation. Percentage depth dose (PDD) and R50 from both calculations are observed. BEAMnrc is simulated electron transport in LINAC head and produced phase space file. This file is used as DOSXYZnrc input to simulated electron transport in phantom. This study is started with commissioning process in water phantom. Commissioning process is adjusted Monte Carlo simulation with Prism RTPS. Commissioning result is used for study of inhomogeneity phantom. Physical parameters of inhomogeneity phantom that varied in this study are: density, location and thickness of tissue. Commissioning result is shown that optimum energy of Monte Carlo simulation for 6 MeV electron beam is 6.8 MeV. This commissioning is used R50 and PDD with Practical length (Rp) as references. From inhomogeneity study, the average deviation for all case on interest region is below 5 %. Based on ICRU recommendations, Prism has good ability to calculate the radiation dose in inhomogeneity tissue.
Mahato, Dip Narayan
This thesis includes x-ray experiments for medical and materials applications and the use of x-ray diffraction data in a first-principles study of electronic structures and hyperfine properties of chemical and biological systems. Polycapillary focusing lenses were used to collect divergent x rays emitted from conventional x-ray tubes and redirect them to form an intense focused beam. These lenses are routinely used in microbeam x-ray fluorescence analysis. In this thesis, their potential application to powder diffraction and focused beam orthovoltage cancer therapy has been investigated. In conventional x-ray therapy, very high energy (˜ MeV) beams are used, partly to reduce the skin dose. For any divergent beam, the dose is necessarily highest at the entry point, and decays exponentially into the tissue. To reduce the skin dose, high energy beams, which have long absorption lengths, are employed, and rotated about the patient to enter from different angles. This necessitates large expensive specialized equipment. A focused beam could concentrate the dose within the patient. Since this is inherently skin dose sparing, lower energy photons could be employed. A primary concern in applying focused beams to therapy is whether the focus would be maintained despite Compton scattering within the tissue. To investigate this, transmission and focal spot sizes as a function of photon energy of two polycapillary focusing lenses were measured. The effects of tissue-equivalent phantoms of different thicknesses on the focal spot size were studied. Scatter fraction and depth dose were calculated. For powder diffraction, the polycapillary optics provide clean Gaussian peaks, which result in angular resolution that is much smaller than the peak width due to the beam convergence. Powder diffraction (also called coherent scatter) without optics can also be used to distinguish between tissue types that, because they have different nanoscale structures, scatter at different angles
Proton affinities of hydrated molecules
Valadbeigi, Younes
2016-09-01
Proton affinities (PA) of non-hydrated, M, and hydrated forms, M(H2O)1,2,3, of 20 organic molecules including alcohols, ethers, aldehydes, ketones and amines were calculated by the B3LYP/6-311++G(d,p) method. For homogeneous families, linear correlations were observed between PAs of the M(H2O)1,2,3 and the PAs of the non-hydrated molecules. Also, the absolute values of the hydration enthalpies of the protonated molecules decreased linearly with the PAs. The correlation functions predicted that for an amine with PA amine with PA > 1100 kJ/mol the PA(M(H2O)) is smaller than the PA.
Affinity driven social networks
Ruyú, B.; Kuperman, M. N.
2007-04-01
In this work we present a model for evolving networks, where the driven force is related to the social affinity between individuals of a population. In the model, a set of individuals initially arranged on a regular ordered network and thus linked with their closest neighbors are allowed to rearrange their connections according to a dynamics closely related to that of the stable marriage problem. We show that the behavior of some topological properties of the resulting networks follows a non trivial pattern.
Energy Technology Data Exchange (ETDEWEB)
Tian Shanxi; Kishimoto, Naoki; Ohno, Koichi
2002-12-15
He I ultraviolet photoelectron spectra and He*(2{sup 3}S) Penning ionization electron spectra have been measured for 1-adamantanol, cyclohexanol and cyclohexanone. Four stable isomeric conformers of cyclohexanol were predicted by Becke's three-parameter hybrid density functional B3LYP/6-31+G(d,p) calculations. Since the orbital reactivity in Penning ionizations is simply related to the electron density extending outside the molecular surface, the theoretical Penning ionization electron spectra were synthesized using the calculated molecular orbital wave functions and ionization potentials. They were in good agreement with the experimental spectra except for the low-electron-energy bands. Collision energy dependence of partial ionization cross sections for the oxygen lone pair orbitals exhibited that there are strong steric hindrances by the neighboring hydrogen atoms in 1-adamantanol and cyclohexanol.
Ma, Zhuang; Zheng, Jiayi; Wang, Song; Gao, Lihong
2017-08-01
It is an effective method to protect components from high power laser damage by using high reflective materials. The rare earth tantalates RETaO4 with high dielectric constant suggests that they may have very high reflectivity, according to the relationship between dielectric constant and reflectivity. In this paper, the crystal structure, electronic structure and optical properties of RETaO4 (RE=Y, La, Sm, Eu, Dy, Er) have been studied by first-principles calculation. The calculated lattice parameters are in good agreement with the previously reported values. With increasing the atomic number of RE (i.e., the number of 4f electrons), 4f electron shell moves from high energy region to low energy region, showing the tendency of moving from conduction band bottom to forbidden gap and then to valence band. The relationship between the electronic structures and optical properties is explored. The electron transitions between O 2p states, RE 4f states and Ta 5d states have a key effect on optical properties such as dielectric function, refractive index, absorption coefficient and reflectivity. For the series of RETaO4, the appearance of the 4f electronic states will obviously promote the improvement of reflectivity. When the 4f states appear at the middle of forbidden gap, the reflectivity reaches the maximum. The reflectivity of EuTaO4 at 1064nm is up to 93.47%, indicating that it has potential applications in the anti-laser radiation area.
Directory of Open Access Journals (Sweden)
Isabella Natali Sora
2012-01-01
Full Text Available Quantum mechanics density functional calculations provided gas-phase electron distributions and proton affinities for several mono- and diaza[5]helicenes; computational results, together with experimental data concerning crystal structures and propensity to methylation of the nitrogen atom(s, provide a basis for designing azahelicene complexes with transition metal ions.
Energy Technology Data Exchange (ETDEWEB)
Tachikawa, Masanori [Quantum Chemistry Division, Graduate School of NanoBioScience, Yokohama City University, 22-2 Seto, Kanazawa, Yokohama 236-0027 (Japan)
2015-12-31
To theoretically demonstrate the binding of a positron to small polarized molecules, we have calculated the vibrational averaged positron affinity (PA) values along the local vibrational contribution with the configuration interaction level of multi-component molecular orbital method. This method can take the electron-positron correlation contribution into account through single electronic - single positronic excitation configurations. The PA values are enhanced by including the local vibrational contribution from vertical PA values due to the anharmonicity of the potential.
Harb, Moussab
2013-08-29
Density functional theory (DFT) and density functional perturbation theory (DFPT) were applied to study the structural, electronic, and optical properties of a (Na2-xCux)Ta4O11 solid solution to accurately calculate the band gap and to predict the optical transitions in these materials using the screened coulomb hybrid (HSE06) exchange-correlation formalism. The calculated density of states showed excellent agreement with UV-vis diffuse reflectance spectra predicting a significant red-shift of the band gap from 4.58 eV (calculated 4.94 eV) to 2.76 eV (calculated 2.60 eV) as copper content increased from 0 to 83.3%. The band gap narrowing in these materials, compared to Na2Ta4O11, results from the incorporation of new occupied electronic states, which are strongly localized on the Cu 3d orbitals, and is located within 2.16-2.34 eV just above the valence band of Na2Ta4O11. These new occupied states, however, possess an electronic character localized on Cu, which makes hole mobility limited in the semiconductor. © 2013 American Chemical Society.
Ásgeirsson, Vilhjálmur; Bauer, Christoph A.
2017-01-01
We introduce a fully stand-alone version of the Quantum Chemistry Electron Ionization Mass Spectra (QCEIMS) program [S. Grimme, Angew. Chem. Int. Ed., 2013, 52, 6306] allowing efficient simulations for molecules composed of elements with atomic numbers up to Z = 86. The recently developed extended tight-binding semi-empirical method GFN-xTB has been combined with QCEIMS, thereby eliminating dependencies on third-party electronic structure software. Furthermore, for reasonable calculations of ionization potentials, as required by the method, a second tight-binding variant, IPEA-xTB, is introduced here. This novel combination of methods allows the automatic, fast and reasonably accurate computation of electron ionization mass spectra for structurally different molecules across the periodic table. In order to validate and inspect the transferability of the method, we perform large-scale simulations for some representative organic, organometallic, and main-group inorganic systems. Theoretical spectra for 23 molecules are compared directly to experimental data taken from standard databases. For the first time, realistic quantum chemistry based EI-MS for organometallic systems like ferrocene or copper(ii)acetylacetonate are presented. Compared to previously used semiempirical methods, GFN-xTB is faster, more robust, and yields overall higher quality spectra. The partially analysed theoretical reaction and fragmentation mechanisms are chemically reasonable and reveal in unprecedented detail the extreme complexity of high energy gas phase ion chemistry including complicated rearrangement reactions prior to dissociation. PMID:28959412
Shin, Hee Won; Ocola, Esther J; Kim, Sunghwan; Laane, Jaan
2014-01-21
The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S1(π,π(*)) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S0 and S1(π,π(*)) electronic states. In each case the decreased π bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S0 and S1(π,π(*)) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S1(π,π(*)) excited state.
Energy Technology Data Exchange (ETDEWEB)
Shin, Hee Won; Ocola, Esther J.; Laane, Jaan, E-mail: laane@mail.chem.tamu.edu [Department of Chemistry, Texas A and M University, College Station, Texas 77843-3255 (United States); Kim, Sunghwan [National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Department of Health and Human Services, 8600 Rockville Pike, Bethesda, Maryland 20894 (United States)
2014-01-21
The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S{sub 1}(π,π{sup *}) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S{sub 0} and S{sub 1}(π,π{sup *}) electronic states. In each case the decreased π bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S{sub 0} and S{sub 1}(π,π{sup *}) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S{sub 1}(π,π{sup *}) excited state.
Shin, Hee Won; Ocola, Esther J.; Kim, Sunghwan; Laane, Jaan
2014-01-01
The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S1(π,π*) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S0 and S1(π,π*) electronic states. In each case the decreased π bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S0 and S1(π,π*) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S1(π,π*) excited state. PMID:25669377
Shin, Hee Won; Ocola, Esther J.; Kim, Sunghwan; Laane, Jaan
2014-01-01
The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S1(π,π*) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S0 and S1(π,π*) electronic states. In each case the decreased π bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S0 and S1(π,π*) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S1(π,π*) excited state.
Energy Technology Data Exchange (ETDEWEB)
Ohl, A [University of Buffalo, Buffalo, NY (United States); Boer, S De [Roswell Park Cancer Institute, Buffalo, NY (United States)
2014-06-01
Purpose: To investigate the differences in relative electron density for different energy (kVp) settings and the effect that these differences have on dose calculations. Methods: A Nuclear Associates 76-430 Mini CT QC Phantom with materials of known relative electron densities was imaged by one multi-slice (16) and one single-slice computed tomography (CT) scanner. The Hounsfield unit (HU) was recorded for each material with energies ranging from 80 to 140 kVp and a representative relative electron density (RED) curve was created. A 5 cm thick inhomogeneity was created in the treatment planning system (TPS) image at a depth of 5 cm. The inhomogeneity was assigned HU for various materials for each kVp calibration curve. The dose was then calculated with the analytical anisotropic algorithm (AAA) at points within and below the inhomogeneity and compared using the 80 kVp beam as a baseline. Results: The differences in RED values as a function of kVp showed the largest variations of 580 and 547 HU for the Aluminum and Bone materials; the smallest differences of 0.6 and 3.0 HU were observed for the air and lung inhomogeneities. The corresponding dose calculations for the different RED values assigned to the 5 cm thick slab revealed the largest differences inside the aluminum and bone inhomogeneities of 2.2 to 6.4% and 4.3 to 7.0% respectively. The dose differences beyond these two inhomogeneities were between 0.4 to 1.6% for aluminum and 1.9 to 2.2 % for bone. For materials with lower HU the calculated dose differences were less than 1.0%. Conclusion: For high CT number materials the dose differences in the phantom calculation as high as 7.0% are significant. This result may indicate that implementing energy specific RED curves can increase dose calculation accuracy.
Raisali, Gholamreza; Mirzakhanian, Lalageh; Masoudi, Seyed Farhad; Semsarha, Farid
2013-01-01
In this work the number of DNA single-strand breaks (SSB) and double-strand breaks (DSB) due to direct and indirect effects of Auger electrons from incorporated (123)I and (125)I have been calculated by using the Geant4-DNA toolkit. We have performed and compared the calculations for several cases: (125)I versus (123)I, source positions and direct versus indirect breaks to study the capability of the Geant4-DNA in calculations of DNA damage yields. Two different simple geometries of a 41 base pair of B-DNA have been simulated. The location of (123)I has been considered to be in (123)IdUrd and three different locations for (125)I. The results showed that the simpler geometry is sufficient for direct break calculations while indirect damage yield is more sensitive to the helical shape of DNA. For (123)I Auger electrons, the average number of DSB due to the direct hits is almost twice the DSB due to the indirect hits. Furthermore, a comparison between the average number of SSB or DSB caused by Auger electrons of (125)I and (123)I in (125)IdUrd and (123)IdUrd shows that (125)I is 1.5 times more effective than (123)I per decay. The results are in reasonable agreement with previous experimental and theoretical results which shows the applicability of the Geant-DNA toolkit in nanodosimetry calculations which benefits from the open-source accessibility with the advantage that the DNA models used in this work enable us to save the computational time. Also, the results showed that the simpler geometry is suitable for direct break calculations, while for the indirect damage yield, the more precise model is preferred.
Twisted Quantum Affine Algebras
Chari, Vyjayanthi; Pressley, Andrew
We give a highest weight classification of the finite-dimensional irreducible representations of twisted quantum affine algebras. As in the untwisted case, such representations are in one-to-one correspondence with n-tuples of monic polynomials in one variable. But whereas in the untwisted case n is the rank of the underlying finite-dimensional complex simple Lie algebra ?, in the twisted case n is the rank of the subalgebra of ? fixed by the diagram automorphism. The way in which such an n-tuple determines a representation is also more complicated than in the untwisted case.
Energy Technology Data Exchange (ETDEWEB)
Benkabou, M. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, H. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Département de Physique, Faculté des Sciences, Université Hassiba Benbouali, Chlef 02000 (Algeria); Abdellaoui, A. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, D., E-mail: rachdj@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique de la Matière, (LPQ3M), Université de Mascara, Mascara 29000 (Algeria); and others
2015-10-25
First-principle calculations are performed to predict the electronic structure and elastic and magnetic properties of CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys. The calculations employ the full-potential linearized augmented plane wave. The exchange-correlations are treated within the generalized gradient approximation of Perdew–Burke and Ernzerhof (GGA-PBE). The electronic structure calculations show that these compounds exhibit a gap in the minority states band and are clearly half-metallic ferromagnets, with the exception of the CoRhMnAl and CoRhMnGa, which are simple ferromagnets that are nearly half metallic in nature. The CoRhMnGe and CoRhMnSi compounds and their magnetic moments are in reasonable agreement with the Slater-Pauling rule, which indicates the half metallicity and high spin polarization for these compounds. At the pressure transitions, these compounds undergo a structural phase transition from the Y-type I → Y-type II phase. We have determined the elastic constants C{sub 11}, C{sub 12} and C{sub 44} and their pressure dependence, which have not previously been established experimentally or theoretically. - Highlights: • Based on DFT calculations, CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys were investigated. • The magnetic phase stability was determined from the total energy calculations. • The mechanical properties were investigated.
DEFF Research Database (Denmark)
Åstrand, Per-Olof; Ramanujam, P.S.; Hvilsted, Søren
2000-01-01
Electronic excitation energies of 16 azobenzene dyes have been calculated by ab initio methods within the second-order polarization propagator approximation (SOPPA). Good agreement with expriment is found for the lowest singlet and triplet states for both the trans- and cis-azobenzene molecules......, the experimental singlet π → π* transitions are reproduced for a set of azobenzene dyes with different electron donor and acceptor groups and the correct shifts in excitation energy are obtained for the different substituents. It has also been demonstrated that ab initio methods can be used to determine suitable...... candidates for azo components used in materials for data storage....
Márquez Cruz, Antonio Marcial; Pacheco, Laura C.; Fernández Sanz, Javier
2017-01-01
We present in this work density functional theory calculations of the structural and electronic properties of (PbS)n nanoparticles with n=4-32. Particular care has been taken on the correct description of their electronic structure by using a hybrid functional including the spin-orbit coupling effects. We demonstrate that the bonding in PbS nanoparticles is quite different from bulk PbS as the six Pb-S bonds around a single Pb atom are found to have a different character while in bulk PbS all...
Energy Technology Data Exchange (ETDEWEB)
Iwai, P; Lins, L Nadler [AC Camargo Cancer Center, Sao Paulo (Brazil)
2016-06-15
Purpose: There is a lack of studies with significant cohort data about patients using pacemaker (PM), implanted cardioverter defibrillator (ICD) or cardiac resynchronization therapy (CRT) device undergoing radiotherapy. There is no literature comparing the cumulative doses delivered to those cardiac implanted electronic devices (CIED) calculated by different algorithms neither studies comparing doses with heterogeneity correction or not. The aim of this study was to evaluate the influence of the algorithms Pencil Beam Convolution (PBC), Analytical Anisotropic Algorithm (AAA) and Acuros XB (AXB) as well as heterogeneity correction on risk categorization of patients. Methods: A retrospective analysis of 19 3DCRT or IMRT plans of 17 patients was conducted, calculating the dose delivered to CIED using three different calculation algorithms. Doses were evaluated with and without heterogeneity correction for comparison. Risk categorization of the patients was based on their CIED dependency and cumulative dose in the devices. Results: Total estimated doses at CIED calculated by AAA or AXB were higher than those calculated by PBC in 56% of the cases. In average, the doses at CIED calculated by AAA and AXB were higher than those calculated by PBC (29% and 4% higher, respectively). The maximum difference of doses calculated by each algorithm was about 1 Gy, either using heterogeneity correction or not. Values of maximum dose calculated with heterogeneity correction showed that dose at CIED was at least equal or higher in 84% of the cases with PBC, 77% with AAA and 67% with AXB than dose obtained with no heterogeneity correction. Conclusion: The dose calculation algorithm and heterogeneity correction did not change the risk categorization. Since higher estimated doses delivered to CIED do not compromise treatment precautions to be taken, it’s recommend that the most sophisticated algorithm available should be used to predict dose at the CIED using heterogeneity correction.
Iwano, Kaoru; Shimoi, Yukihiro
2009-02-01
Density-functional theory (DFT) calculations are performed based on the high-temperature structure of (EDO-TTF)2PF6, a quasi-one-dimensional molecular compound that shows both thermal and photoinduced phase transitions. In this structure, the EDO-TTF molecules are one-dimensionally aligned, accompanied with weak dimerization. Contrary to a common sense, our DFT calculations reveal that the pair having a shorter mutual distance has a weaker intermolecular coupling than the pair with a longer one; the latter is appropriate to be called an electronic dimer. We also estimate the corresponding transfer energies and discuss their relevance to spin correlations and optical excitations.
Su, Lin; Du, Xining; Liu, Tianyu; Xu, X. George
2014-06-01
An electron-photon coupled Monte Carlo code ARCHER - Accelerated Radiation-transport Computations in Heterogeneous EnviRonments - is being developed at Rensselaer Polytechnic Institute as a software testbed for emerging heterogeneous high performance computers that utilize accelerators such as GPUs. This paper presents the preliminary code development and the testing involving radiation dose related problems. In particular, the paper discusses the electron transport simulations using the class-II condensed history method. The considered electron energy ranges from a few hundreds of keV to 30 MeV. For photon part, photoelectric effect, Compton scattering and pair production were modeled. Voxelized geometry was supported. A serial CPU code was first written in C++. The code was then transplanted to the GPU using the CUDA C 5.0 standards. The hardware involved a desktop PC with an Intel Xeon X5660 CPU and six NVIDIA Tesla™ M2090 GPUs. The code was tested for a case of 20 MeV electron beam incident perpendicularly on a water-aluminum-water phantom. The depth and later dose profiles were found to agree with results obtained from well tested MC codes. Using six GPU cards, 6x106 electron histories were simulated within 2 seconds. In comparison, the same case running the EGSnrc and MCNPX codes required 1645 seconds and 9213 seconds, respectively. On-going work continues to test the code for different medical applications such as radiotherapy and brachytherapy.
Energy Technology Data Exchange (ETDEWEB)
Dorado, B.
2010-09-15
Uranium dioxide UO{sub 2} is the standard nuclear fuel used in pressurized water reactors. During in-reactor operation, the fission of uranium atoms yields a wide variety of fission products (FP) which create numerous point defects while slowing down in the material. Point defects and FP govern in turn the evolution of the fuel physical properties under irradiation. In this study, we use electronic structure calculations in order to better understand the fuel behavior under irradiation. In particular, we investigate point defect behavior, as well as the stability of three volatile FP: iodine, krypton and xenon. In order to take into account the strong correlations of uranium 5f electrons in UO{sub 2}, we use the DFT+U approximation, based on the density functional theory. This approximation, however, creates numerous metastable states which trap the system and induce discrepancies in the results reported in the literature. To solve this issue and to ensure the ground state is systematically approached as much as possible, we use a method based on electronic occupancy control of the correlated orbitals. We show that the DFT+U approximation, when used with electronic occupancy control, can describe accurately point defect and fission product behavior in UO{sub 2} and provide quantitative information regarding point defect transport properties in the oxide fuel. (author)
Peng, Bo; Kowalski, Karol
2017-09-12
The representation and storage of two-electron integral tensors are vital in large-scale applications of accurate electronic structure methods. Low-rank representation and efficient storage strategy of integral tensors can significantly reduce the numerical overhead and consequently time-to-solution of these methods. In this work, by combining pivoted incomplete Cholesky decomposition (CD) with a follow-up truncated singular vector decomposition (SVD), we develop a decomposition strategy to approximately represent the two-electron integral tensor in terms of low-rank vectors. A systematic benchmark test on a series of 1-D, 2-D, and 3-D carbon-hydrogen systems demonstrates high efficiency and scalability of the compound two-step decomposition of the two-electron integral tensor in our implementation. For the size of the atomic basis set, Nb, ranging from ∼100 up to ∼2,000, the observed numerical scaling of our implementation shows [Formula: see text] versus [Formula: see text] cost of performing single CD on the two-electron integral tensor in most of the other implementations. More importantly, this decomposition strategy can significantly reduce the storage requirement of the atomic orbital (AO) two-electron integral tensor from [Formula: see text] to [Formula: see text] with moderate decomposition thresholds. The accuracy tests have been performed using ground- and excited-state formulations of coupled cluster formalism employing single and double excitations (CCSD) on several benchmark systems including the C60 molecule described by nearly 1,400 basis functions. The results show that the decomposition thresholds can be generally set to 10-4 to 10-3 to give acceptable compromise between efficiency and accuracy.
Sempau, J; Wilderman, S J; Bielajew, A F
2000-08-01
A new Monte Carlo (MC) algorithm, the 'dose planning method' (DPM), and its associated computer program for simulating the transport of electrons and photons in radiotherapy class problems employing primary electron beams, is presented. DPM is intended to be a high accuracy MC alternative to the current generation of treatment planning codes which rely on analytical algorithms based on an approximate solution of the photon/electron Boltzmann transport equation. For primary electron beams, DPM is capable of computing 3D dose distributions (in 1 mm3 voxels) which agree to within 1% in dose maximum with widely used and exhaustively benchmarked general-purpose public-domain MC codes in only a fraction of the CPU time. A representative problem, the simulation of 1 million 10 MeV electrons impinging upon a water phantom of 128(3) voxels of 1 mm on a side, can be performed by DPM in roughly 3 min on a modern desktop workstation. DPM achieves this performance by employing transport mechanics and electron multiple scattering distribution functions which have been derived to permit long transport steps (of the order of 5 mm) which can cross heterogeneity boundaries. The underlying algorithm is a 'mixed' class simulation scheme, with differential cross sections for hard inelastic collisions and bremsstrahlung events described in an approximate manner to simplify their sampling. The continuous energy loss approximation is employed for energy losses below some predefined thresholds, and photon transport (including Compton, photoelectric absorption and pair production) is simulated in an analogue manner. The delta-scattering method (Woodcock tracking) is adopted to minimize the computational costs of transporting photons across voxels.