Ab initio electronic structure and optical conductivity of bismuth tellurohalides
Schwalbe, Sebastian; Starke, Ronald; Schober, Giulio A H; Kortus, Jens
2016-01-01
We investigate the electronic structure, dielectric and optical properties of bismuth tellurohalides BiTeX (X = I, Cl, Br) by means of all-electron density functional theory. In particular, we present the ab initio conductivities and dielectric tensors calculated over a wide frequency range, and compare our results with the recent measurements by Akrap et al. , Makhnev et al. , and Rusinov et al. . We show how the low-frequency branch of the optical conductivity can be used to identify characteristic intra- and interband transitions between the Rashba spin-split bands in all three bismuth tellurohalides. We further calculate the refractive indices and dielectric constants, which in turn are systematically compared to previous predictions and measurements. We expect that our quantitative analysis will contribute to the general assessment of bulk Rashba materials for their potential use in spintronics devices.
All-electron ab initio investigations of the electronic states of the NiC molecule
DEFF Research Database (Denmark)
Shim, Irene; Gingerich, Karl. A.
1999-01-01
The low-lying electronic states of NiC are investigated by all-electron ab initio multi-configuration self-consistent-field (CASSCF) calculations including relativistic corrections. The electronic structure of NiC is interpreted as perturbed antiferromagnetic couplings of the localized angular...
Ab initio calculations on twisted graphene/hBN: Electronic structure and STM image simulation
Correa, J. D.; Cisternas, E.
2016-09-01
By performing ab initio calculations we obtained theoretical scanning tunneling microscopy (STM) images and studied the electronic properties of graphene on a hexagonal boron-nitrite (hBN) layer. Three different stack configurations and four twisted angles were considered. All calculations were performed using density functional theory, including van der Waals interactions as implemented in the SIESTA ab initio package. Our results show that the electronic structure of graphene is preserved, although some small changes are induced by the interaction with the hBN layer, particularly in the total density of states at 1.5 eV under the Fermi level. When layers present a twisted angle, the density of states shows several van Hove singularities under the Fermi level, which are associated to moiré patterns observed in theoretical STM images.
Energy Technology Data Exchange (ETDEWEB)
Herbig, Alexander
2016-02-12
An ab-initio electronic structure method for substitutionally disordered real materials is developed within a pseudopotential density functional theory approach. The method is validated against exact diagonalization and for simple disordered CuZn alloys. The developed method is applied to iron-based superconductors. In particular, band renormalization effects due to various chemical substitutions in BaFe{sub 2}As{sub 2} are investigated and their Cooper pair breaking effects are compared.
Ab initio electronic properties of dual phosphorus monolayers in silicon
DEFF Research Database (Denmark)
Drumm, Daniel W.; Per, Manolo C.; Budi, Akin;
2014-01-01
, investigating the fundamental electronic properties of monolayer pairs. Quantitative band splittings and the electronic density are presented, along with effects of the layers’ relative alignment and comments on disordered systems, and for the first time, the effective electronic widths of such device...
Ab initio phonon coupling and optical response of hot electrons in plasmonic metals
Brown, Ana M; Narang, Prineha; Goddard, William A; Atwater, Harry A
2016-01-01
Ultrafast laser measurements probe the non-equilibrium dynamics of excited electrons in metals with increasing temporal resolution. Electronic structure calculations can provide a detailed microscopic understanding of hot electron dynamics, but a parameter-free description of pump-probe measurements has not yet been possible, despite intensive research, because of the phenomenological treatment of electron-phonon interactions. We present ab initio predictions of the electron-temperature dependent heat capacities and electron-phonon coupling coefficients of plasmonic metals. We find substantial differences from free-electron and semi-empirical estimates, especially in noble metals above transient electron temperatures of 2000 K, because of the previously-neglected strong dependence of electron-phonon matrix elements on electron energy. We also present first-principles calculations of the electron-temperature dependent dielectric response of hot electrons in plasmonic metals, including direct interband and phon...
Electronic Structure of Silicon Nanowires Matrix from Ab Initio Calculations.
Monastyrskii, Liubomyr S; Boyko, Yaroslav V; Sokolovskii, Bogdan S; Potashnyk, Vasylyna Ya
2016-12-01
An investigation of the model of porous silicon in the form of periodic set of silicon nanowires has been carried out. The electronic energy structure was studied using a first-principle band method-the method of pseudopotentials (ultrasoft potentials in the basis of plane waves) and linearized mode of the method of combined pseudopotentials. Due to the use of hybrid exchange-correlation potentials (B3LYP), the quantitative agreement of the calculated value of band gap in the bulk material with experimental data is achieved. The obtained results show that passivation of dangling bonds with hydrogen atoms leads to substantial transformation of electronic energy structure. At complete passivation of the dangling silicon bonds by hydrogen atoms, the band gap value takes the magnitude which substantially exceeds that for bulk silicon. The incomplete passivation gives rise to opposite effect when the band gap value decreases down the semimetallic range.
Ab initio calculations of yttrium nitride: structural and electronic properties
Energy Technology Data Exchange (ETDEWEB)
Zerroug, S.; Ali Sahraoui, F. [Universite Ferhat Abbas, Laboratoire d' Optoelectronique et Composants, Departement de Physique, Setif (Algeria); Bouarissa, N. [King Khalid University, Department of Physics, Faculty of Science, P.O. Box 9004, Abha (Saudi Arabia)
2009-11-15
Using first principles total energy calculations within the full-potential linearized augmented plane wave method, we have studied the structural and electronic properties of yttrium nitride (YN) in the three phases, namely wurtzite, caesium chloride and rocksalt structures. The calculations are performed at zero and under hydrostatic pressure. In agreement with previous findings, it is found that the favored phase for YN is the rocksalt-like structure. We predict that at zero pressure YN in the rocksalt structure is a semiconductor with an indirect bandgap of 0.8 eV. A phase transition from a rocksalt to a caesium chloride structure is found to occur at {proportional_to}134 GPa. Besides, a transition from an indirect ({gamma}-X) bandgap semiconductor to a direct (X-X) one is predicted at pressure of {proportional_to}84 GPa. For the electron effective mass of rocksalt YN, these are the first results, to our knowledge. The information derived from the present study may be useful for the use of YN as an active layer in electronic devices such as diodes and transistors. (orig.)
Ab Initio Study of Electronic States of Astrophysically Important Molecules
Valiev, R. R.; Berezhnoy, A. A.; Minaev, B. F.; Chernov, V. E.; Cherepanov, V. N.
2016-08-01
A study of electronic states of LiO, NaO, KO, MgO, and CaO molecules has been performed. Potential energy curves of the investigated molecules have been constructed within the framework of the XMC-QDPT2 method. Lifetimes and efficiencies of photolysis mechanisms of these monoxides have been estimated within the framework of an analytical model of photolysis. The results obtained show that oxides of the considered elements in the exospheres of the Moon and Mercury are destroyed by solar photons during the first ballistic flight.
Energy Technology Data Exchange (ETDEWEB)
Razee, S.S.A.; Staunton, J.B. [Department of Physics, University of Warwick, Coventry (United Kingdom); Ginatempo, B.; Bruno, E. [Dipartimento di Fisica and Unita INFM, Universita di Messina, Messina (Italy); Pinski, F.J. [Department of Physics, University of Cincinnati, OH (United States)
2001-09-24
A theory is presented for describing the effects of annealing magnetic alloys in magnetic fields. It has an ab initio spin-polarized relativistic Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) electronic structure basis and uses the framework of concentration waves. Alloys which would otherwise be soft magnets are found experimentally to develop directional chemical order and significant uniaxial anisotropy when annealed in magnetic fields. Our approach is able to provide a quantitative description of these effects together with the underlying electronic mechanisms. We describe applications to the soft magnetic alloys permalloy and FeCo. (author)
Quantum chemistry the development of ab initio methods in molecular electronic structure theory
Schaefer III, Henry F
2004-01-01
This guide is guaranteed to prove of keen interest to the broad spectrum of experimental chemists who use electronic structure theory to assist in the interpretation of their laboratory findings. A list of 150 landmark papers in ab initio molecular electronic structure methods, it features the first page of each paper (which usually encompasses the abstract and introduction). Its primary focus is methodology, rather than the examination of particular chemical problems, and the selected papers either present new and important methods or illustrate the effectiveness of existing methods in predi
Energy Technology Data Exchange (ETDEWEB)
Yamaji, Youhei [Quantum-Phase Electronics Center, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-8656 (Japan)
2015-12-31
Recently, condensed-matter ab initio approaches to strongly correlated electrons confined in crystalline solids have been developed and applied to transition-metal oxides and molecular conductors. In this paper, an ab initio scheme based on constrained random phase approximations and localized Wannier orbitals is applied to a spin liquid candidate Na{sub 2}IrO{sub 3} and is shown to reproduce experimentally observed specific heat.
Ab initio study of structural, electronic, and thermal properties of Ir1-xRhx alloys
Directory of Open Access Journals (Sweden)
Sh. Ahmed
2015-06-01
Full Text Available The structural, electronic, mechanical and thermal properties of Ir1-xRhx alloys was studied systematically using ab initio density functional theory at different concentration (x = 0.00, 0.25, 0.50, 0.75, 1.00. The Special Quasirandom Structure method was used to make the alloys with FCC structure with four atoms per unit cell. The ground state properties such as lattice constant and bulk modulus were calculated to find the equilibrium atomic position for stable alloys. The calculated ground state properties are in good agreement with the experimental and previously presented other theoretical data. The electronic band structure and density of states were calculated to study the electronic properties for these alloys at different concentration. The electronic properties substantiate metallic behavior of alloys. The first principle density functional perturbation theory as implemented in quasiharmonic approximation was used for the calculation of thermal properties. We have calculated the thermal properties such the Debye temperatures, vibration energy, entropy, constant-volume specific heat and internal energy. The ab initio linear-response method was used for phonon densities of states calculations.
Ab initio determination of effective electron-phonon coupling factor in copper
Ji, Pengfei; Zhang, Yuwen
2016-04-01
The electron temperature Te dependent electron density of states g (ε), Fermi-Dirac distribution f (ε), and electron-phonon spectral function α2 F (Ω) are computed as prerequisites before achieving effective electron-phonon coupling factor Ge-ph. The obtained Ge-ph is implemented into a molecular dynamics (MD) and two-temperature model (TTM) coupled simulation of femtosecond laser heating. By monitoring temperature evolutions of electron and lattice subsystems, the result utilizing Ge-ph from ab initio calculation shows a faster decrease of Te and increase of Tl than those using Ge-ph from phenomenological treatment. The approach of calculating Ge-ph and its implementation into MD-TTM simulation is applicable to other metals.
Ab initio determination of effective electron-phonon coupling factor in copper
Ji, Pengfei
2016-01-01
The electron temperature T_e dependent electron density of states g({\\epsilon}), Fermi-Dirac distribution f({\\epsilon}), and electron-phonon spectral function {\\alpha}^2 F({\\Omega}) are computed as prerequisites before achieving effective electron-phonon coupling factor. The obtained is implemented into a molecular dynamics (MD) and two-temperature model (TTM) coupled simulation of femtosecond laser heating. By monitoring temperature evolutions of electron and lattice subsystems, the result utilizing G_(e-ph) from ab initio calculation, shows a faster decrease of T_e and increase of T_l than those using G_(e-ph) from phenomenological treatment. The approach of calculating G_(e-ph) and its implementation into MD-TTM simulation is applicable to other metals.
Nomura, Yusuke; Arita, Ryotaro
2015-12-01
We formulate an ab initio downfolding scheme for electron-phonon-coupled systems. In this scheme, we calculate partially renormalized phonon frequencies and electron-phonon coupling, which include the screening effects of high-energy electrons, to construct a realistic Hamiltonian consisting of low-energy electron and phonon degrees of freedom. We show that our scheme can be implemented by slightly modifying the density functional-perturbation theory (DFPT), which is one of the standard methods for calculating phonon properties from first principles. Our scheme, which we call the constrained DFPT, can be applied to various phonon-related problems, such as superconductivity, electron and thermal transport, thermoelectricity, piezoelectricity, dielectricity, and multiferroicity. We believe that the constrained DFPT provides a firm basis for the understanding of the role of phonons in strongly correlated materials. Here, we apply the scheme to fullerene superconductors and discuss how the realistic low-energy Hamiltonian is constructed.
Ji, Pengfei
2016-01-01
By combining ab initio quantum mechanics calculation and Drude model, electron temperature and lattice temperature dependent electron thermal conductivity is calculated and implemented into a multiscale model of laser material interaction, which couples the classical molecular dynamics and two-temperature model. The results indicated that the electron thermal conductivity obtained from ab initio calculation leads to faster thermal diffusion than that using the electron thermal conductivity from empirical determination, which further induces deeper melting region, larger number of density waves travelling inside the copper film and more various speeds of atomic clusters ablated from the irradiated film surface.
Ab initio study of the low-lying electronic states of the CaO molecule
Energy Technology Data Exchange (ETDEWEB)
Khalil, Hossain; Brites, Vincent; Quere, Frederic Le [Universite Paris-Est, Laboratoire de Modelisation et Simulation Multi Echelle, UMR 8208 CNRS, Batiment Lavoisier, 5 boulevard Descartes, Champs sur Marne, 77454 Marne-la-Vallee, Cedex 2 (France); Leonard, Celine, E-mail: celine.leonard@univ-paris-est.fr [Universite Paris-Est, Laboratoire de Modelisation et Simulation Multi Echelle, UMR 8208 CNRS, Batiment Lavoisier, 5 boulevard Descartes, Champs sur Marne, 77454 Marne-la-Vallee, Cedex 2 (France)
2011-07-28
Graphical abstract: Highly correlated ab initio calculations have been performed for an accurate determination of the electronic structure of the low-lying electronic states of the CaO molecule. The computations are done using the aug-cc-pV5Z basis set for O and the cc-pCV5Z for Ca. The potential energy curves for the molecular states correlating to the lowest three asymptotes are calculated at the CASSCF level. The potential curves of the lowest five molecular states, X{sup 1}{Sigma}{sup +}, a{sup 3}{Pi}, A'{sup 1{Pi}}, b{sup 3}{Sigma}{sup +} and A{sup 1}{Sigma}{sup +}, and the corresponding dipole moment functions have been determined using internally contracted multi-reference configuration interaction approaches. The spectroscopic constants associated with these electronic states are compared to experimental values. The corresponding electronic wavefunctions have also been analyzed using the dipole moment functions. Display Omitted Highlights: {yields} The five lowest electronic states of Cao have been determined ab initio at a high level of accuracy. {yields} Large active space, core-valence correlation and configuration interaction are required. {yields} The multi-configurational nature of the electronic ground state is confirmed as well as its monovalent and divalent ionic nature using dipole moment analysis. {yields} These interacting potentials will serve for future obtention of spin-rovibronic levels. - Abstract: Highly correlated ab initio calculations have been performed for an accurate determination of the electronic structure of the low-lying electronic states of the CaO molecule. The computations are done using the aug-cc-pV5Z basis set for O and the cc-pCV5Z for Ca. The potential energy curves for the molecular states correlating to the lowest three asymptotes are calculated at the CASSCF level. The potential curves of the lowest five molecular states, X{sup 1}{Sigma}{sup +}, a{sup 3}{Pi}, A'{sup 1}{Pi}, b{sup 3}{Sigma}{sup +} and A{sup 1
Energy Technology Data Exchange (ETDEWEB)
Kimberg, Victor, E-mail: victor.kimberg@pks.mpi.de [Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden (Germany); Miron, Catalin, E-mail: miron@synchrotron-soleil.fr [Synchrotron SOLEIL, l’Orme des Merisiers, Saint-Aubin, BP 48, FR-91192 Gif-sur-Yvette Cedex (France)
2014-08-15
Highlights: • Some studies related to the vibrational wave functions mapping phenomenon are reviewed. • The core-excited vibrational wave functions were mapped using dissociative and bound final states. • High-resolution experimental data is accompanied by ab initio calculations. • The mapping phenomenon allows one to extract constants of the molecular potentials. • The mapping techniques are general and can be applied for the study of many systems. - Abstract: The recent development of high brightness 3{sup rd} generation soft X-ray sources and high energy resolution electron spectrometers made it possible to accurately trace quantum phenomena associated to the vibrational dynamics in core-excited molecules. The present paper reviews the recent results on mapping of vibrational wave functions and molecular potentials based on electron spectroscopy. We discuss and compare the mapping phenomena in various systems, stressing the advantages of the resonant X-ray scattering for studying of the nuclear dynamics and spectroscopic constants of small molecules. The experimental results discussed in the paper are most often accompanied by state-of-the-art ab initio calculations allowing for a deeper understanding of the quantum effects. Besides its fundamental interest, the vibrational wave function mapping is shown to be useful for the analysis of core- and valence-excited molecular states based on the reflection principle.
Tunneling of electrons via rotor-stator molecular interfaces: combined ab initio and model study
Petreska, Irina; Pejov, Ljupco; Kocarev, Ljupco
2015-01-01
Tunneling of electrons through rotor-stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons' formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that confirmation dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previ...
Ab-initio calculations on two-electron ions in strongly coupled plasma environment
Bhattacharyya, S; Mukherjee, T K
2015-01-01
In this work, the controversy between the interpretations of recent measurements on dense aluminum plasma created with Linac coherent light sources (LCLS) X-ray free electron laser (FEL) and Orion laser has been addressed. In both kind of experiments, helium-like and hydrogen-like spectral lines are used for plasma diagnostics . However, there exist no precise theoretical calculations for He-like ions within dense plasma environment. The strong need for an accurate theoretical estimates for spectral properties of He-like ions in strongly coupled plasma environment leads us to perform ab initio calculations in the framework of Rayleigh-Ritz variation principle in Hylleraas coordinates where ion-sphere potential is used. An approach to resolve the long-drawn problem of numerical instability for evaluating two-electron integrals with extended basis inside a finite domain is presented here. The present values of electron densities corresponding to disappearance of different spectral lines obtained within the fram...
Gao, Haiyuan; Li, Meijiao; Guo, Zhendong; Chen, Hongshen; Jin, Zhonghe; Yu, Bin
2011-01-01
Electronic transport properties of monolayer graphene with extreme physical bending up to 90o angle are studied using ab Initio first-principle calculations. The importance of key structural parameters including step height, curvature radius and bending angle are discussed how they modify the transport properties of the deformed graphene sheet comparing to the corresponding flat ones. The local density of state reveals that energy state modification caused by the physical bending is highly localized. It is observed that the transport properties of bent graphene with a wide range of geometrical configurations are insensitive to the structural deformation in the low-energy transmission spectra, even in the extreme case of bending. The results support that graphene, with its superb electromechanical robustness, could serve as a viable material platform in a spectrum of applications such as photovoltaics, flexible electronics, OLED, and 3D electronic chips.
Ab Initio Quantum Monte Carlo Simulation of the Warm Dense Electron Gas in the Thermodynamic Limit
Dornheim, Tobias; Groth, Simon; Sjostrom, Travis; Malone, Fionn D.; Foulkes, W. M. C.; Bonitz, Michael
2016-10-01
We perform ab initio quantum Monte Carlo (QMC) simulations of the warm dense uniform electron gas in the thermodynamic limit. By combining QMC data with the linear response theory, we are able to remove finite-size errors from the potential energy over the substantial parts of the warm dense regime, overcoming the deficiencies of the existing finite-size corrections by Brown et al. [Phys. Rev. Lett. 110, 146405 (2013)]. Extensive new QMC results for up to N =1000 electrons enable us to compute the potential energy V and the exchange-correlation free energy Fxc of the macroscopic electron gas with an unprecedented accuracy of |Δ V |/|V |,|Δ Fxc|/|F |xc˜10-3 . A comparison of our new data to the recent parametrization of Fxc by Karasiev et al. [Phys. Rev. Lett. 112, 076403 (2014)] reveals significant deviations to the latter.
Ab initio phonon coupling and optical response of hot electrons in plasmonic metals
Brown, Ana M.; Sundararaman, Ravishankar; Narang, Prineha; Goddard, William A.; Atwater, Harry A.
2016-08-01
Ultrafast laser measurements probe the nonequilibrium dynamics of excited electrons in metals with increasing temporal resolution. Electronic structure calculations can provide a detailed microscopic understanding of hot electron dynamics, but a parameter-free description of pump-probe measurements has not yet been possible, despite intensive research, because of the phenomenological treatment of electron-phonon interactions. We present ab initio predictions of the electron-temperature dependent heat capacities and electron-phonon coupling coefficients of plasmonic metals. We find substantial differences from free-electron and semiempirical estimates, especially in noble metals above transient electron temperatures of 2000 K, because of the previously neglected strong dependence of electron-phonon matrix elements on electron energy. We also present first-principles calculations of the electron-temperature dependent dielectric response of hot electrons in plasmonic metals, including direct interband and phonon-assisted intraband transitions, facilitating complete theoretical predictions of the time-resolved optical probe signatures in ultrafast laser experiments.
Galler, Anna; Gunacker, Patrik; Tomczak, Jan; Thunström, Patrik; Held, Karsten
Recently, approaches such as the dynamical vertex approximation (D ΓA) or the dual-fermion method have been developed. These diagrammatic approaches are going beyond dynamical mean field theory (DMFT) by including nonlocal electronic correlations on all length scales as well as the local DMFT correlations. Here we present our efforts to extend the D ΓA methodology to ab-initio materials calculations (ab-initio D ΓA). Our approach is a unifying framework which includes both GW and DMFT-type of diagrams, but also important nonlocal correlations beyond, e.g. nonlocal spin fluctuations. In our multi-band implementation we are using a worm sampling technique within continuous-time quantum Monte Carlo in the hybridization expansion to obtain the DMFT vertex, from which we construct the reducible vertex function using the two particle-hole ladders. As a first application we show results for transition metal oxides. Support by the ERC project AbinitioDGA (306447) is acknowledged.
2011-01-01
The geometric, electronic structure, effect of the substitution, and structure physical-chemistry relationship for oxazoles derivatives have been studied by ab initio and DFT theory. In the present work, the calculated values, namely, net charges, bond lengths, dipole moments, electron affinities, heats of formation, and QSAR properties are reported and discussed in terms of the reactivity of oxazole derivatives.
DEFF Research Database (Denmark)
Gorelik, Tatiana E; van de Streek, Jacco; Kilbinger, Andreas F M
2012-01-01
Ab-initio crystal structure analysis of organic materials from electron diffraction data is presented. The data were collected using the automated electron diffraction tomography (ADT) technique. The structure solution and refinement route is first validated on the basis of the known crystal stru...
Ab initio electron scattering cross-sections and transport in liquid xenon
Boyle, G. J.; McEachran, R. P.; Cocks, D. G.; Brunger, M. J.; Buckman, S. J.; Dujko, S.; White, R. D.
2016-09-01
Ab initio fully differential cross-sections for electron scattering in liquid xenon are developed from a solution of the Dirac-Fock scattering equations, using a recently developed framework (Boyle et al 2015 J. Chem. Phys. 142 154507) which considers multipole polarizabilities, a non-local treatment of exchange, and screening and coherent scattering effects. A multi-term solution of Boltzmann’s equation accounting for the full anisotropic nature of the differential cross-section is used to calculate transport properties of excess electrons in liquid xenon. The results were found to agree to within 25% of the measured mobilities and characteristic energies over the reduced field range of 10-4-1 Td. The accuracies are comparable to those achieved in the gas phase. A simple model, informed by highly accurate gas-phase cross-sections, is presented to improve the liquid cross-sections, which was found to enhance the accuracy of the transport coefficient calculations.
Minimal parameter implicit solvent model for ab initio electronic structure calculations
Dziedzic, Jacek; Skylaris, Chris-Kriton; Mostofi, Arash A; Payne, Mike C
2011-01-01
We present an implicit solvent model for ab initio electronic structure calculations which is fully self-consistent and is based on direct solution of the nonhomogeneous Poisson equation. The solute cavity is naturally defined in terms of an isosurface of the electronic density according to the formula of Fattebert and Gygi (J. Comp. Chem. 23, 6 (2002)). While this model depends on only two parameters, we demonstrate that by using appropriate boundary conditions and dispersion-repulsion contributions, solvation energies obtained for an extensive test set including neutral and charged molecules show dramatic improvement compared to existing models. Our approach is implemented in, but not restricted to, a linear-scaling density functional theory (DFT) framework, opening the path for self-consistent implicit solvent DFT calculations on systems of unprecedented size, which we demonstrate with calculations on a 2615-atom protein-ligand complex.
Ab initio study of the electronic structure andelastic properties of Al5C3N
Institute of Scientific and Technical Information of China (English)
Xu Xue-Wen; Hu Long; Yu Xiao; Lu Zun-Ming; Fan Ying; Li Yang-xian; Tang Cheng-Chun
2011-01-01
We investigate the electronic structure,chemical bonding and elastic properties of the hexagonal aluminum carbonitride,Al5C3N,by ab initio calculations.Al5C3N is a semiconductor with a narrow indirect gap of 0.81 eV.The valence bands below the Fermi level (EF) originate from the hybridized Al p-C p and Al p-N p states.The calculated bulk and Young's moduli are 201 GPa and 292 GPa,which are slightly lower than those of Ti3SiC2.The values of the bulk-to-shear-modulus and bulk-modulus-to-c44 are 1.73 and 1.97,respectively,which axe higher than those of Ti2AlCand Ti2AlN,indicating that Al5C3N is a ductile ceramic.
Energy Technology Data Exchange (ETDEWEB)
Moradian, Rostam [Physics Department, Faculty of Science, Razi University, Kermanshah (Iran, Islamic Republic of); Nano Science and Technology Research Center, Razi University, Kermanshah (Iran, Islamic Republic of); Department of Nano Science, Computational Physical Science Research Laboratory, Institute for Studies in Theoretical Physics and Mathematics (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of)], E-mail: moradian.rostam@gmail.com; Behzad, Somayeh; Chegel, Raad [Physics Department, Faculty of Science, Razi University, Kermanshah (Iran, Islamic Republic of)
2008-10-01
By using ab initio density functional theory the structural and electronic properties of isolated and bundled (8,0) and (6,6) silicon carbide nanotubes (SiCNTs) are investigated. Our results show that for such small diameter nanotubes the inter-tube interaction causes a very small radial deformation, while band splitting and reduction of the semiconducting energy band gap are significant. We compared the equilibrium interaction energy and inter-tube separation distance of (8,0) SiCNT bundle with (10,0) carbon nanotube (CNT) bundle where they have the same radius. We found that there is a larger inter-tube separation and weaker inter-tube interaction in the (8,0) SiCNT bundle with respect to (10,0) CNT bundle, although they have the same radius.
Electron Transport through Polyene Junctions in between Carbon Nanotubes: an Ab Initio Realization
Chen, Yiing-Rei; Chen, Kai-Yu; Dou, Kun-Peng; Tai, Jung-Shen; Lee, Hsin-Han; Kaun, Chao-Cheng
With both ab initio and tight-binding model calculations, we study a system of polyene bridged armchair carbon nanotube electrodes, considering one-polyene and two-polyene cases, to address aspects of quantum transport through junctions with multiple conjugated molecules. The ab initio results of the two-polyene cases not only show the interference effect in transmission, but also the sensitive dependence of such effect on the combination of relative contact sites, which agrees nicely with the tight-binding model. Moreover, we show that the discrepancy mainly brought by ab initio relaxation provides an insight into the influence upon transmission spectra, from the junction's geometry, bonding and effective potential. This work was supported by the Ministry of Science and Technology of the Republic of China under Grant Nos. 99-2112-M-003-012-MY2 and 103-2622-E-002-031, and the National Center for Theoretical Sciences of Taiwan.
Giovannetti, Gianluca; Brocks, Geert; Brink, van den Jeroen
2008-01-01
We investigate the effect that potassium intercalation has on the electronic structure of copper phthalocyanine (CuPc) molecular crystals by means of ab initio density functional calculations. Pristine CuPc (in its alpha and beta structures) is found to be an insulator containing local magnetic mome
Silvestrelli, P.-L.; Alavi, A.; Parrinello, M.; Frenkel, D.
1997-01-01
The method of ab initio molecular dynamics, based on finite-temperature density-functional theory, is used to simulate laser heating of crystalline silicon. We found that a high concentration of excited electrons dramatically weakens the covalent bonding. As a result the system undergoes a melting t
An ab initio study on single electron transfer between ClO2 and phenol
Institute of Scientific and Technical Information of China (English)
崔崇威; 黄君礼
2004-01-01
The SET mechanism between chlorine dioxide (ClO2 ) and phenol was studied by using ab initio method at 4-31G* level. Geometries of the reactants, intermediate and products of the reaction were optimized and the single point energy calculations of the species were performed. The relative structure data of the reactants, intermediate and products are given. The SET mechanism between ClO2 and phenol was confirmed by ab initio calculations. The reaction is exothermic about 200. 88 k J/mol.
Hoy, Erik P; Mazziotti, David A
2015-08-14
Tensor factorization of the 2-electron integral matrix is a well-known technique for reducing the computational scaling of ab initio electronic structure methods toward that of Hartree-Fock and density functional theories. The simplest factorization that maintains the positive semidefinite character of the 2-electron integral matrix is the Cholesky factorization. In this paper, we introduce a family of positive semidefinite factorizations that generalize the Cholesky factorization. Using an implementation of the factorization within the parametric 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)], we study several inorganic molecules, alkane chains, and potential energy curves and find that this generalized factorization retains the accuracy and size extensivity of the Cholesky factorization, even in the presence of multi-reference correlation. The generalized family of positive semidefinite factorizations has potential applications to low-scaling ab initio electronic structure methods that treat electron correlation with a computational cost approaching that of the Hartree-Fock method or density functional theory.
Energy Technology Data Exchange (ETDEWEB)
Hoy, Erik P.; Mazziotti, David A., E-mail: damazz@uchicago.edu [Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637 (United States)
2015-08-14
Tensor factorization of the 2-electron integral matrix is a well-known technique for reducing the computational scaling of ab initio electronic structure methods toward that of Hartree-Fock and density functional theories. The simplest factorization that maintains the positive semidefinite character of the 2-electron integral matrix is the Cholesky factorization. In this paper, we introduce a family of positive semidefinite factorizations that generalize the Cholesky factorization. Using an implementation of the factorization within the parametric 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)], we study several inorganic molecules, alkane chains, and potential energy curves and find that this generalized factorization retains the accuracy and size extensivity of the Cholesky factorization, even in the presence of multi-reference correlation. The generalized family of positive semidefinite factorizations has potential applications to low-scaling ab initio electronic structure methods that treat electron correlation with a computational cost approaching that of the Hartree-Fock method or density functional theory.
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.
Ab initio transport calculations of molecular wires with electron-phonon couplings
Hirose, Kenji; Kobayashi, Nobuhiko
2009-03-01
Understanding of electron transport through nanostructures becomes important with the advancement of fabrication process to construct atomic-scale devices. Due to the drastic change of transport properties by contact conditions to electrodes in local electric fields, first-principles calculation approaches are indispensable to understand and characterize the transport properties of nanometer-scale molecular devices. Here we study the transport properties of molecular wires between metallic electrodes, especially focusing on the effects of contacts to electrodes and of the electron-phonon interactions. We use an ab initio calculation method based on the scattering waves, which are obtained by the recursion-transfer-matrix (RTM) method, combined with non-equilibrium Green's function (NEGF) method including the electron-phonon scatterings. We find that conductance shows exponential behaviors as a function of the length of molecular wires due to tunneling process determined by the HOMO-LUMO energy gap. From the voltage drop behaviors inside the molecular wires, we show that the contact resistances are dominant source for the bias drop and thus are related to local heating. We will present the electron-phonon coupling effects at contact on the inelastic scattering and discuss on the local heating and local temperature, comparing them with those of metallic atomic wires.
Tunneling of electrons via rotor-stator molecular interfaces: Combined ab initio and model study
Petreska, Irina; Ohanesjan, Vladimir; Pejov, Ljupčo; Kocarev, Ljupčo
2016-07-01
Tunneling of electrons through rotor-stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons' formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that conformation-dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previous work where we investigated the coherent transport via strongly coupled delocalized orbital by application of Non-equilibrium Green's Function Formalism.
Ab-initio electron scattering cross-sections and transport in liquid xenon
Boyle, Greg; Cocks, Daniel; Brunger, Michael; Buckman, Steve; Dujko, Sasa; White, Ron
2016-01-01
Ab-initio electron - liquid phase xenon fully differential cross-sections for electrons scattering in liquid xenon are developed from a solution of the Dirac-Fock scattering equations, using a recently developed framework [1] which considers multipole polarizabilities, a non-local treatment of exchange, and screening and coherent scattering effects. A multi-term solution of Boltzmann's equation accounting for the full anisotropic nature of the differential cross-section is used to calculate transport properties of excess electrons in liquid xenon. The results were found to agree to within 25% of the measured mobilities and characteristic energies over the reduced field range of 10^{-4} to 1 Td. The accuracies are comparable to those achieved in the gas phase. A simple model, informed by highly accurate gas-phase cross-sections, is presented to transform highly accurate gas-phase cross-sections to improve the liquid cross-sections, which was found to enhance the accuracy of the transport coefficient calculatio...
Energy Technology Data Exchange (ETDEWEB)
Giuliani, A. [Synchrotron Soleil, DISCO beamline, L' Orme des Merisiers, 91 - Gif-sur-Yvette (France); Giuliani, A. [Cepia, Institut National de la Recherche Agronomique (INRA), 44 - Nantes (France); Limiao-Vieira, P. [Lisboa Univ. Nova, Lab. de Colisoes Atomicas e Moleculares, CEFITEC, Dept. de Fysica, Caparica (Portugal); Limao-Vieira, P.; Mason, N. [Open Univ., Centre of Molecular and Optical Sciences, Dept. of Physics and Astronomy, Milton Keynes, MK (United Kingdom); Duflot, D. [Lille Univ. des Sciences et Technologies, Lab. de Physique des Lasers, Atomes et Molecules (PhLAM), UMR CNRS 8523, Centre d' Etudes et de Recherches Lasers et Applications, CERLA, FR CNRS 2416, 59 - Villeneuve d' Ascq (France); Milosavljevic, A.R.; Marinkovic, B.P. [Laboratory for atomic collision processes, Institute of Physics, Belgrade, Serbia (Yugoslavia); Hoffmann, S.V. [Aarhus Univ., Institute for Storage Ring Facilities (Denmark); Delwiche, J.; Hubin-Franskin, M.J. [Liege Univ., Laboratoire de Spectroscopie d' Electrons Diffuses, Institut de Chimie (Belgium)
2009-01-15
The electronic spectroscopy of isolated tetrahydrofuran (THF) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 5.8 - 10.6 eV with absolute cross-section measurements derived. In addition, an electron energy loss spectrum was recorded at 100 eV and 10 degrees over the 5 - 11.4 eV range. The He(I) photoelectron spectrum was also collected to quantify ionisation energies in the 9 - 16.1 eV spectral region. These experiments are supported by the first high-level ab initio calculations performed on the excited states of the neutral molecule and on the ground state of the positive ion. The excellent agreement between the theoretical results and the measurements allows us to solve several discrepancies concerning the electronic state spectroscopy of THF. The present work reconsiders the question of the lowest energy conformers of the molecule and its population distribution at room temperature. (authors)
Ab initio calculations of the electronic structure and bonding characteristics of LaB6
Hossain, Faruque M.; Riley, Daniel P.; Murch, Graeme E.
2005-12-01
Lanthanum hexaboride ( LaB6 , NIST SRM-660a) is widely used as a standard reference material for calibrating the line position and line shape parameters of powder diffraction instruments. The accuracy of this calibration technique is highly dependent on how completely the reference material is characterized. Critical to x-ray diffraction, this understanding must include the valence of the La atomic position, which in turn will influence the x-ray form factor (f) and hence the diffracted intensities. The electronic structure and bonding properties of LaB6 have been investigated using ab initio plane-wave pseudopotential total energy calculations. The electronic properties and atomic bonding characteristics were analyzed by estimating the energy band structure and the density of states around the Fermi energy level. The calculated energy band structure is consistent with previously reported experimental findings; de Haas-van Alphen and two-dimensional angular correlation of electron-positron annihilation radiation. In addition, the bond strengths and types of atomic bonds in the LaB6 compound were estimated by analyzing the Mulliken charge density population. The calculated result revealed the coexistence of covalent, ionic, and metallic bonding in the LaB6 system and partially explains its high efficiency as a thermionic emitter.
Ab initio study of structural, electronic, and thermal properties of Pt1-xPdx alloys
Ahmed, Shabbir; Zafar, Muhammad; Shakil, M.; Choudhary, M. A.; Hashmi, Muhammad Raza-Ur-Rehman
2017-01-01
We report a systematic theoretical study of Pt1-xPdx alloys using ab initio density functional theory (DFT) by pseudo potential method. We have used super cell approach to investigate structural, electronic and thermal properties of Platinum (Pt), Palladium (Pd) and their alloys Pt1-xPdx(x = 0.00, 0.25, 0.50, 0.75, 1.00). The calculated lattice constants and bulk moduli are in good agreement with available literature data. The results of electronic properties revealed that the alloys are metallic in nature. The thermal properties were investigated through density functional perturbation theory (DFPT) and quasi-harmonic approximation. The contribution to the free energy from the lattice vibration was calculated using the phonon densities of states (DOS) derived by means of the linear-response theory. The DFPT with quasi-harmonic approximation methods was applied to determine the phonon DOS and thermal quantities i.e., the Debye temperatures, vibration energy, entropy and constant-volume specific heat.
Ab-initio Electronic, Transport and Related Properties of Zinc Blende Boron Arsenide (zb-BAs)
Nwigboji, Ifeanyi H.; Malozovsky, Yuriy; Bagayoko, Diola
We present results from ab-initio, self-consistent density functional theory (DFT) calculations of electronic, transport, and bulk properties of zinc blende boron arsenide (zb-BAs). We utilized a local density approximation (LDA) potential and the linear combination of atomic orbital (LCAO) formalism. Our computational technique follows the Bagayoko, Zhao, and Williams method, as enhanced by Ekuma and Franklin. Our results include electronic energy bands, densities of states, and effective masses. We explain the agreement between these findings, including the indirect band gap, and available, corresponding, experimental ones. This work confirms the capability of DFT to describe accurately properties of materials, provided the computations adhere to the conditions of validity of DFT [AIP Advances, 4, 127104 (2014)]. Acknowledgments: This work was funded in part by the National Science Foundation (NSF) and the Louisiana Board of Regents, through LASiGMA [Award Nos. EPS- 1003897, NSF (2010-15)-RII-SUBR] and NSF HRD-1002541, the US Department of Energy - National, Nuclear Security Administration (NNSA) (Award No. DE- NA0002630), LaSPACE, and LONI-SUBR.
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...
Ab initio calculation of structural stability, electronic and optical properties of Ag{sub 2}Se
Energy Technology Data Exchange (ETDEWEB)
Rameshkumar, S.; Jayalakshmi, V., E-mail: karthikajayam@yahoo.co.in [Department of Physics, SRM University, Ramapuram Campus, Chennai – 600089 (India); Jaiganesh, G. [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam – 603102 (India); Palanivel, B. [Department of Physics, Pondicherry Engineering College, Puducherry – 605014 (India)
2015-06-24
The structural stability, electronic and optical properties of Ag{sub 2}Se compound is studied using ab initio packages. Ag{sub 2}Se is found to crystallize in orthorhombic structure with two different space groups i.e. P2{sub 1}2{sub 1}2{sub 1} (No. 19) and P222{sub 1} (No. 17). For this compound in these two space groups, the total energy has been computed as a function of volume. Our calculated results suggest that the P2{sub 1}2{sub 1}2{sub 1}–phase is more stable than that of the P222{sub 1}–phase. The band structure calculation show that Ag{sub 2}Se is semimetallic with an overlap of about 0.014 eV in P2{sub 1}2{sub 1}2{sub 1}–phase whereas is metallic in nature in P222{sub 1}–phase. Moreover, the optical properties including the dielectric function, energy loss spectrum are obtained and analysed.
Adane, Legesse; Bharatam, Prasad V.
In several literature reports biuret and its sulfur analogs are reported to exist in their diketo form with general formula H2N bond CX bond NH bond CY bond NH2 (X = O, Y = O, biuret; X = Y = S, dithiobiuret; and X = O, Y = S, thiobiuret). On the other hand, recently reported results on the electronic structure of biguanide analogs (X = Y = NH)demonstrated that a form equivalent to diketo is not the preferred structure. Thus, a systematic ab initio study on the tautomeric preferences of biuret and its sulfur analogs (dithiobiuret and thiobiuret) has been carried out. The results indicate that an interplay of conjugative stabilization and intramolecular hydrogen bonding to play a role in tautomeric preferences. Energy and geometric parameters, natural bond orbital analyses have been employed to understand the chemistry of the title compounds. The results indicate that unlike biguanides, these compounds prefer diketo forms containing hydrogen on the bridging nitrogen (N4) and in a trans-arrangement (1a-4a). However, tautomerization of these keto forms to the corresponding enol isomers was also found to be highly probable.
Energy Technology Data Exchange (ETDEWEB)
Borges, P. D., E-mail: pdborges@gmail.com, E-mail: lscolfaro@txstate.edu; Scolfaro, L., E-mail: pdborges@gmail.com, E-mail: lscolfaro@txstate.edu [Department of Physics, Texas State University, San Marcos, Texas 78666 (United States)
2014-12-14
The thermoelectric properties of indium nitride in the most stable wurtzite phase (w-InN) as a function of electron and hole concentrations and temperature were studied by solving the semiclassical Boltzmann transport equations in conjunction with ab initio electronic structure calculations, within Density Functional Theory. Based on maximally localized Wannier function basis set and the ab initio band energies, results for the Seebeck coefficient are presented and compared with available experimental data for n-type as well as p-type systems. Also, theoretical results for electric conductivity and power factor are presented. Most cases showed good agreement between the calculated properties and experimental data for w-InN unintentionally and p-type doped with magnesium. Our predictions for temperature and concentration dependences of electrical conductivity and power factor revealed a promising use of InN for intermediate and high temperature thermoelectric applications. The rigid band approach and constant scattering time approximation were utilized in the calculations.
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.
Ji, Pengfei; Zhang, Yuwen
2016-03-01
On the basis of ab initio quantum mechanics (QM) calculation, the obtained electron heat capacity is implemented into energy equation of electron subsystem in two temperature model (TTM). Upon laser irradiation on the copper film, energy transfer from the electron subsystem to the lattice subsystem is modeled by including the electron-phonon coupling factor in molecular dynamics (MD) and TTM coupled simulation. The results show temperature and thermal melting difference between the QM-MD-TTM integrated simulation and pure MD-TTM coupled simulation. The successful construction of the QM-MD-TTM integrated simulation provides a general way that is accessible to other metals in laser heating.
Ji, Pengfei
2016-01-01
On the basis of ab initio quantum mechanics (QM) calculation, the obtained electron heat capacity is implemented into energy equation of electron subsystem in two temperature model (TTM). Upon laser irradiation on the copper film, energy transfer from the electron subsystem to the lattice subsystem is modeled by including the electron-phonon coupling factor in molecular dynamics (MD) and TTM coupled simulation. The results show temperature and thermal melting difference between the QM-MD-TTM integrated simulation and pure MD-TTM coupled simulation. The successful construction of the QM-MD-TTM integrated simulation provide a general way that is accessible to other metals in laser heating.
Ab Initio Investigations of the Excited Electronic States of CaOCa
Fawzy, Wafaa M.; Heaven, Michael
2016-06-01
Chemical bonding in alkaline earth hypermetalic oxides is of fundamental interest. Previous Ab initio studies of CaOCa predicted a centrosymmetric linear geometry for both the 1Σg^+ ground state and the low lying triplet 3Σu^+ state. However, there have been no reports concerning the higher energy singlet and triplet states. The present work is focused on characterization of the potential energy surface (PES) of the excited 1Σu^+ state (assuming a centrosymmetric linear geometry) and obtaining predictions for the 1Σu^+←1Σg^+ vibronic transitions. We employed the multireference configuration interaction (MRCISD) method with state-averaged, full-valence complete active space self-consistent field (SA-FV-CASSCF) wavefunctions. In these calculations, the active space consisted of ten valence electrons in twelve orbitals, where all the valence electrons were correlated. Contributions of higher excitation and relativistic effects were taken into account using the Davidson correction and the Douglas-Kroll (DK) Hamiltonian, respectively. The correlation-consistent polarized weighed core-valence quadruple zeta basis set (cc-pwCVQZ-DK) was used for all three atoms. The full level of theory is abbreviated as SA-FV-CASSCF (10,12)-MRCISD-Q/cc-pwCVQZ-DK. The calculations were carried out using the MOLPRO2012 suite of programs. For the centrosymmetric linear geometry in all states, initial investigations of one-dimensional radial cuts provided equilibrium bond distances of 2.034 {Å}, 2.034 {Å}, and 1.999 {Å} for the 1Σg^+ , 3Σu^+ , and 1Σu^+ states, respectively. The vertical excitation frequency of the 1Σu^+←1Σg^+ optical transition was calculated to occur at 14801 wn. These predictions were followed by spectroscopic searches by Heaven et al. Indeed, rotationally resolved vibronic progressions were recorded in the vicinity of the predicted electronic band origin. Calculation of the three-dimensional PES showed that the potential minimum in the 1Σu^+ corresponds
Ab initio study of structural, electronic, and thermal properties of Ir_{1-x}Rh_{x} alloys
Directory of Open Access Journals (Sweden)
Sh. Ahmed
2015-06-01
Full Text Available The structural, electronic, mechanical and thermal properties of Ir_{1-x}Rh_{x} alloys was studied systematically using ab initio density functional theory at different concentration (x = 0.00, 0.25, 0.50, 0.75, 1.00. The Special Quasirandom Structure method was used to make the alloys with FCC structure with four atoms per unit cell. The ground state properties such as lattice constant and bulk modulus were calculated to find the equilibrium atomic position for stable alloys. The calculated ground state properties are in good agreement with the experimental and previously presented other theoretical data. The electronic band structure and density of states were calculated to study the electronic properties for these alloys at different concentration. The electronic properties substantiate metallic behavior of alloys. The first principle density functional perturbation theory as implemented in quasiharmonic approximation was used for the calculation of thermal properties. We have calculated the thermal properties such the Debye temperatures, vibration energy, entropy, constant-volume specific heat and internal energy. The ab initio linear-response method was used for phonon densities of states calculations.
Many-body effects on the electronic and optical properties of Si nanowires from ab initio approaches
Energy Technology Data Exchange (ETDEWEB)
Palummo, M.; Del Sole, R. [European Theoretical Spectroscopy Facility (ETSF), CNR-INFM-SMC, Roma (Italy); Dipartimento di Fisica - Universita di Roma, ' Tor Vergata' , Roma (Italy); Ossicini, S. [European Theoretical Spectroscopy Facility (ETSF), Reggio Emilia (Italy); Dipartimento di Scienze e Metodi dell' Ingegneria, Universita di Modena e Reggio Emilia (Italy)
2010-08-15
The study of semiconducting nanowires is one of the most rapidly growing research areas in materials science and nanotechnology, not only from the point of view of the possible applications, but also regarding the use of the latest developments in the theory. In this paper, we review the general ab initio many-body theory and methods and resume some of our very recent results regarding the structural, electronic, and optical properties of Silicon nanowires (Si-NWs), outlining both the reached achievements and some of the technical aspects necessary to obtain them. (Abstract Copyright [2010], Wiley Periodicals, Inc.)
Grebenshchikov, Sergy Yu.
2013-01-01
The global potential energy surfaces of the first six singlet electronic states of CO$_2$, 1---3$^1/!A'$ and 1---3$^1/!A"$ are constructed using high level ab initio calculations. In linear molecule, they correspond to $\\tilde{X}^1\\Sigma_g^+$, $1^1\\Delta_u$, $1^1\\Sigma_u^-$, and $1^1\\Pi_g$. The calculations accurately reproduce the known benchmarks for all states and establish missing benchmarks for future calculations. The calculated states strongly interact at avoided crossings and true int...
Institute of Scientific and Technical Information of China (English)
ZHANG Zhi-jie; LIU Yu-hua; L(U) Zhong-yuan; LI Ze-sheng
2009-01-01
The rotational isomeric state(RIS) model was constructed for poly(vinylidene chloride)(PVDC) based on quantum chemistry calculations. The statistical weighted parameters were obtained from RIS representations and ab initio energies of conformers for model molecules 2,2,4,4-tetrachloropentane(TCP) and 2,2,4,4,6, 6-hexachlorohep-tane(HCH). By employing the RIS method, the characteristic ratio C∞ was calculated for PVDC. The calculated cha-racteristic ratio for PVDC is in good agreement with experiment result. Additionally, we studied the influence of the statistical weighted parameters on C∞ by calculating δC∞/δlnw. According to the values of δC∞/δlnw, the effects of second-order Cl-CH2 pentane type interaction and Cl-Cl long range interaction on C∞ were found to be important. In contrast, first-order interaction is unimportant.
DEFF Research Database (Denmark)
Fürst, Joachim Alexander; Hashemi, J.; Markussen, Troels;
2009-01-01
Fullerene functionalized carbon nanotubes-NanoBuds-form a novel class of hybrid carbon materials, which possesses many advantageous properties as compared to the pristine components. Here, we report a theoretical study of the electronic transport properties of these compounds. We use both ab init...
Gharabaghi, Masumeh; Shahbazian, Shant
2016-12-01
In this letter the conceptual and computational implications of the Hartree product type nuclear wavefunction introduced recently within the context of the ab initio non-Born-Oppenheimer Nuclear-electronic orbital (NEO) methodology are considered. It is demonstrated that this wavefunction may imply a pseudo-adiabatic separation of the nuclei and electrons and each nucleus is conceived as a quantum oscillator while a non-Coulombic effective Hamiltonian is deduced for electrons. Using the variational principle this Hamiltonian is employed to derive a modified set of single-component Hartree-Fock equations which are equivalent to the multi-component version derived previously within the context of the NEO and, easy to be implemented computationally.
Gharabaghi, Masumeh
2016-01-01
In this letter the conceptual and computational implications of the Hartree product type nuclear wavefunction introduced recently within context of the ab initio non-Born-Oppenheimer Nuclear-electronic orbital (NEO) methodology are considered. It is demonstrated that this wavefunction may imply a pseudo-adiabatic separation of the nuclei and electrons and each nucleus is conceived as a quantum oscillator while a non-Coulombic effective Hamiltonian is deduced for electrons. Using variational principle this Hamiltonian is used to derive a modified set of single-component Hartree-Fock equations which are equivalent to the multi-component version derived previously within context of the NEO and, easy to be implemented computationally.
Dornheim, Tobias; Sjostrom, Travis; Malone, Fionn D; Foulkes, W M C; Bonitz, Michael
2016-01-01
We perform \\emph{ab initio} quantum Monte Carlo (QMC) simulations of the warm dense uniform electron gas in the thermodynamic limit. By combining QMC data with linear response theory we are able to remove finite-size errors from the potential energy over the entire warm dense regime, overcoming the deficiencies of the existing finite-size corrections by Brown \\emph{et al.}~[PRL \\textbf{110}, 146405 (2013)]. Extensive new QMC results for up to $N=1000$ electrons enable us to compute the potential energy $V$ and the exchange-correlation free energy $F_{xc}$ of the macroscopic electron gas with an unprecedented accuracy of $|\\Delta V|/|V|, |\\Delta F_{xc}|/|F|_{xc} \\sim 10^{-3}$. A comparison of our new data to the recent parametrization of $F_{xc}$ by Karasiev {\\em et al.} [PRL {\\bf 112}, 076403 (2014)] reveals significant inaccuracies of the latter.
Roy, Soumendra K.; Jian, Tian; Lopez, Gary V.; Li, Wei-Li; Su, Jing; Bross, David H.; Peterson, Kirk A.; Wang, Lai-Sheng; Li, Jun
2016-02-01
The observation of the gaseous UFO- anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state of UFO- is linear with an O-U-F structure and a 3H4 spectral term derived from a U 7sσ25fφ15fδ1 electron configuration, whereas the ground state of neutral UFO has a 4H7/2 spectral term with a U 7sσ15fφ15fδ1 electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. The strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations.
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....
Reciprocity Theorems for Ab Initio Force Calculations
Wei, C; Mele, E J; Rappe, A M; Lewis, Steven P.; Rappe, Andrew M.
1996-01-01
We present a method for calculating ab initio interatomic forces which scales quadratically with the size of the system and provides a physically transparent representation of the force in terms of the spatial variation of the electronic charge density. The method is based on a reciprocity theorem for evaluating an effective potential acting on a charged ion in the core of each atom. We illustrate the method with calculations for diatomic molecules.
Directory of Open Access Journals (Sweden)
Jose Ángel Silva-Guillén
2016-10-01
Full Text Available Semiconducting transition metal dichalcogenides present a complex electronic band structure with a rich orbital contribution to their valence and conduction bands. The possibility to consider the electronic states from a tight-binding model is highly useful for the calculation of many physical properties, for which first principle calculations are more demanding in computational terms when having a large number of atoms. Here, we present a set of Slater–Koster parameters for a tight-binding model that accurately reproduce the structure and the orbital character of the valence and conduction bands of single layer MX 2 , where M = Mo, W and X = S, Se. The fit of the analytical tight-binding Hamiltonian is done based on band structure from ab initio calculations. The model is used to calculate the optical conductivity of the different compounds from the Kubo formula.
Devi, Assa Aravindh Sasikala
2014-05-01
Investigations on freestanding binary and ternary clusters of Fe (x) Co (y) Ir (z) (x + y + z = 5, 6) are carried out using ab initio density functional theory techniques. The geometry, chemical order, binding energy, magnetic moment and electronic structure of the clusters are analyzed for the entire range of composition. Composition dependent structural transition is observed in the five atom clusters, while octahedral geometry prevailed in clusters with six atoms. Both the clusters show increment in binding energy with the increase in number of heterogeneous bonds. Analysis based on the chemical order parameter indicates that clusters favor mixing rather than segregation. The clusters exhibit ferromagnetic ordering and the inter-dependence of optimal cluster geometry to the magnetic moments and electronic structure is observed.
Petit, L; Paudyal, D; Mudryk, Y; Gschneidner, K A; Pecharsky, V K; Lüders, M; Szotek, Z; Banerjee, R; Staunton, J B
2015-11-13
We explain a profound complexity of magnetic interactions of some technologically relevant gadolinium intermetallics using an ab initio electronic structure theory which includes disordered local moments and strong f-electron correlations. The theory correctly finds GdZn and GdCd to be simple ferromagnets and predicts a remarkably large increase of Curie temperature with a pressure of +1.5 K kbar(-1) for GdCd confirmed by our experimental measurements of +1.6 K kbar(-1). Moreover, we find the origin of a ferromagnetic-antiferromagnetic competition in GdMg manifested by noncollinear, canted magnetic order at low temperatures. Replacing 35% of the Mg atoms with Zn removes this transition, in excellent agreement with long-standing experimental data.
Odell, Anders
2011-10-03
The influence of the electrode\\'s Fermi surface on the transport properties of a photoswitching molecule is investigated with state-of-the-art ab initio transport methods. We report results for the conducting properties of the two forms of dithienylethene attached either to Ag or to nonmagnetic Ni leads. The I-V curves of the Ag/dithienylethene/Ag device are found to be very similar to those reported previously for Au. In contrast, when Ni is used as the electrode material the zero-bias transmission coefficient is profoundly different as a result of the role played by the Ni d bands in the bonding between the molecule and the electrodes. Intriguingly, despite these differences the overall conducting properties depend little on the electrode material. We thus conclude that electron transport in dithienylethene is, for the cases studied, mainly governed by the intrinsic electronic structure of the molecule. © 2011 American Physical Society.
Mills, Jeffrey D; Ben-Nun, Michal; Rollin, Kyle; Bromley, Michael W J; Li, Jiabo; Hinde, Robert J; Winstead, Carl L; Sheehy, Jeffrey A; Boatz, Jerry A; Langhoff, Peter W
2016-08-25
Continuing attention has addressed incorportation of the electronically dynamical attributes of biomolecules in the largely static first-generation molecular-mechanical force fields commonly employed in molecular-dynamics simulations. We describe here a universal quantum-mechanical approach to calculations of the electronic energy surfaces of both small molecules and large aggregates on a common basis which can include such electronic attributes, and which also seems well-suited to adaptation in ab initio molecular-dynamics applications. In contrast to the more familiar orbital-product-based methodologies employed in traditional small-molecule computational quantum chemistry, the present approach is based on an "ex-post-facto" method in which Hamiltonian matrices are evaluated prior to wave function antisymmetrization, implemented here in the support of a Hilbert space of orthonormal products of many-electron atomic spectral eigenstates familiar from the van der Waals theory of long-range interactions. The general theory in its various forms incorporates the early semiempirical atoms- and diatomics-in-molecules approaches of Moffitt, Ellison, Tully, Kuntz, and others in a comprehensive mathematical setting, and generalizes the developments of Eisenschitz, London, Claverie, and others addressing electron permutation symmetry adaptation issues, completing these early attempts to treat van der Waals and chemical forces on a common basis. Exact expressions are obtained for molecular Hamiltonian matrices and for associated energy eigenvalues as sums of separate atomic and interaction-energy terms, similar in this respect to the forms of classical force fields. The latter representation is seen to also provide a long-missing general definition of the energies of individual atoms and of their interactions within molecules and matter free from subjective additional constraints. A computer code suite is described for calculations of the many-electron atomic eigenspectra and
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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)
Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Taylor, Peter R.
1989-01-01
Recent advances in electronic structure theory and the availability of high speed vector processors have substantially increased the accuracy of ab initio potential energy surfaces. The recently developed atomic natural orbital approach for basis set contraction has reduced both the basis set incompleteness and superposition errors in molecular calculations. Furthermore, full CI calculations can often be used to calibrate a CASSCF/MRCI approach that quantitatively accounts for the valence correlation energy. These computational advances also provide a vehicle for systematically improving the calculations and for estimating the residual error in the calculations. Calculations on selected diatomic and triatomic systems will be used to illustrate the accuracy that currently can be achieved for molecular systems. In particular, the F + H2 yields HF + H potential energy hypersurface is used to illustrate the impact of these computational advances on the calculation of potential energy surfaces.
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Alemany, Manuel M. G. [Universidad de Santiago de Compostela; Longo, Roberto [Universidad de Santiago de Compostela; Gallego, Luis [Universidad de Santiago de Compostela; Gonzales, D. J. [Universidad de Valladolid; Gonzales, L. E. [Universidad de Valladolid; Tiago, Murilo L [ORNL; Chelikowsky, James [University of Texas, Austin
2007-01-01
We performed a comprehensive study of the static, dynamic and electronic properties of liquid Pb at T = 650 kelvins, density 0.0309 angstroms^{-3} by means of 216-particle ab initio molecular dynamics simulations based on a real-space implementation of pseudopotentials constructed within density-functional theory. The predicted results and available experimental data are very in good agreement, which confirms the adequacy of this technique to achieve a reliable description of the behavior of liquid metals, including their dynamic properties. Although some of the computed properties of liquid Pb are similar to those of simple liquid metals, others differ markedly. Our results show that an appropriate description of liquid Pb requires the inclusion of relativistic effects in the determination of the pseudopotentials of Pb.
Mogulkoc, Y.; Ciftci, Y. O.; Kabak, M.; Colakoglu, K.
2014-07-01
The structural, elastic, thermodynamic, electronic and vibrational properties of CsCl-type TbMg have been studied by performing ab initio calculations based on density functional theory using the Vienna Ab initio Simulation Package (VASP). The exchange correlation potential within the generalized-gradient approximation (GGA) of projector augmented wave (PAW) method is used. The calculated structural parameters, such as the lattice constant, bulk modulus, its pressure derivative, formation energy and second-order elastic constants are presented in this paper. The obtained results are compared with related experimental and theoretical studies. The electronic band calculations, total density of states (DOS), partial DOS and charge density are also presented. Formation enthalpy and Cauchy pressure are determined. In order to obtain more information the elastic properties such as Zener anisotropy factor, Poisson’s ratio, Young modulus, isotropic shear modulus, Debye temperature and melting point have been carried out. The elastic constants are calculated in zero and different pressure ranges (0-50 GPa) with bulk modulus. We have performed the thermodynamic properties of TbMg by using quasi-harmonic Debye model. The temperature and pressure variation of the volume, bulk modulus, and thermal expansion coefficient have been predicted over a pressure range of 0-25 GPa for of TbMg. Pressure dependence of the anisotropy factors, Young’s modulus, Poisson’s ratios, bulk modulus and axis compressibility of TbMg are presented along different directions and planes. Finally, the phonon dispersion curves are presented for TbMg.
Jaeger, C.R.; Debowski, M.A.; Manners, I.; Vancso, G.J.
1999-01-01
Ab initio molecular orbital calculations at the MP2/6-31G* level of theory have been used to study the molecular geometry, electronic structure, and the thermal stability of six-membered phosphazene and heterophosphazene rings. The studies included the phosphazene ring [NPCl2]3, the carbophosphazene
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Perevalov, T. V., E-mail: timson@isp.nsc.ru; Gritsenko, V. A., E-mail: grits@isp.nsc.ru [Russian Academy of Sciences, Institute of Semiconductor Physics, Siberian Branch (Russian Federation)
2011-02-15
The electronic structure of TiO{sub 2} rutile with oxygen vacancies, which is a promising insulator, has been analyzed. The ab initio density functional calculations, as well as the comparative analysis of the results obtained in the {sigma}-GGA spin-polarized generalized approximation and those obtained by the {sigma}-GGA + U method with allowance for Coulomb correlations of d electrons titanium atoms in the Hartree-Fock approximation for the Hubbard model, have been performed. It has been found that the effective electron mass in rutile is anisotropic and there are both light (m{sub e}{sup *} = (0.6-0.8)m{sub 0}, where m{sub 0} is the free-electron mass) and heavy (m{sub e}* > 1m{sub 0}) electrons, whereas holes in rutile are only heavy (m{sub e}* Greater-Than-Or-Slanted-Equal-To 2m{sub 0}). It has been shown that the {sigma}-GGA + U method gives a deep occupied level in the band gap and that an oxygen vacancy in rutile is an electron and hole trap.
Agrawal, P M; Malshe, M; Narulkar, R; Raff, L M; Hagan, M; Bukkapatnum, S; Komanduri, R
2009-02-05
Previous methods proposed for obtaining analytic potential-energy surfaces (PES) from ab initio electronic structure calculations are not self-starting. They generally require that the sampling of configuration space important in the reaction dynamics of the process being investigated be initiated by using chemical intuition or a previously developed semiempirical potential-energy surface. When the system under investigation contains four or more atoms undergoing three- and four-center reactions in addition to bond scission processes, obtaining a sufficiently converged initial sampling can be very difficult due to the extremely large volume of configuration space that is important in the reaction dynamics. It is shown that by combining direct dynamics (DD) with previously reported molecular dynamics (MD), novelty sampling (NS), and neural network (NN) methods, an analytical surface suitable for MD computations for large systems may be obtained. Application of the method to the investigation of N-O bond scission and cis-trans isomerization reactions of HONO followed by comparison of the resulting neural network potential-energy surface to one obtained by using a semiempirical potential to initiate the sampling shows that the two potential surfaces are the same within the fitting accuracy of the surfaces. It is concluded that the combination of direct dynamics, molecular dynamics, novelty sampling, and neural network fitting provides a self-starting, robust, and accurate DD/MD/NS/NN method for the execution of first-principles, ab initio, molecular dynamics studies in systems containing four or more atoms which are undergoing simultaneous two-, three-, and four-center reactions.
Ab initio calculation of electron-phonon coupling in monoclinic β-Ga2O3 crystal
Ghosh, Krishnendu; Singisetti, Uttam
2016-08-01
The interaction between electrons and vibrational modes in monoclinic β-Ga2O3 is theoretically investigated using ab-initio calculations. The large primitive cell of β-Ga2O3 gives rise to 30 phonon modes all of which are taken into account in transport calculation. The electron-phonon interaction is calculated under density functional perturbation theory and then interpolated using Wannier-Fourier interpolation. The long-range interaction elements between electrons and polar optical phonon (POP) modes are calculated separately using the Born effective charge tensor. The direction dependence of the long-range POP coupling in a monoclinic crystal is explored and is included in the transport calculations. Scattering rate calculations are done using the Fermi golden rule followed by solving the Boltzmann transport equation using the Rode's method to estimate low field mobility. A room temperature mobility of 115 cm2/V s is observed. Comparison with recent experimentally reported mobility is done for a wide range of temperatures (30 K-650 K). It is also found that the POP interaction dominates the electron mobility under low electric field conditions. The relative contribution of the different POP modes is analyzed and the mode 21 meV POP is found to have the highest impact on low field electron mobility at room temperature.
Long, Run; Fang, Weihai; Akimov, Alexey V
2016-02-18
We report ab initio time-domain simulations of nonradiative electron-hole recombination and electronic dephasing in ideal and defect-containing monolayer black phosphorus (MBP). Our calculations predict that the presence of phosphorus divacancy in MBP (MBP-DV) substantially reduces the nonradiative recombination rate, with time scales on the order of 1.57 ns. The luminescence line width in ideal MBP of 150 meV is 2.5 times larger than MBP-DV at room temperature, and is in excellent agreement with experiment. We find that the electron-hole recombination in ideal MBP is driven by the 450 cm(-1) vibrational mode, whereas the recombination in the MBP-DV system is driven by a broad range of vibrational modes. The reduced electron-phonon coupling and increased bandgap in MBP-DV rationalize slower recombination in this material, suggesting that electron-phonon energy losses in MBP can be minimized by creating suitable defects in semiconductor device material.
Roy, Soumendra K; Jian, Tian; Lopez, Gary V; Li, Wei-Li; Su, Jing; Bross, David H; Peterson, Kirk A; Wang, Lai-Sheng; Li, Jun
2016-02-28
The observation of the gaseous UFO(-) anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state of UFO(-) is linear with an O-U-F structure and a (3)H4 spectral term derived from a U 7sσ(2)5fφ(1)5fδ(1) electron configuration, whereas the ground state of neutral UFO has a (4)H(7/2) spectral term with a U 7sσ(1)5fφ(1)5fδ(1) electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. The strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations.
Energy Technology Data Exchange (ETDEWEB)
Saalfrank, Peter [Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam (Germany); Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Juaristi, J. I. [Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 Donostia-San Sebastián (Spain); Departamento de Física de Materiales, Facultad de Químicas UPV/EHU, Apartado 1072, 20018 Donostia-San Sebastián (Spain); Alducin, M.; Muiño, R. Díez [Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, 20018 Donostia-San Sebastián (Spain); Blanco-Rey, M. [Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Spain); Departamento de Física de Materiales, Facultad de Químicas UPV/EHU, Apartado 1072, 20018 Donostia-San Sebastián (Spain)
2014-12-21
Using density functional theory and Ab Initio Molecular Dynamics with Electronic Friction (AIMDEF), we study the adsorption and dissipative vibrational dynamics of hydrogen atoms chemisorbed on free-standing lead films of increasing thickness. Lead films are known for their oscillatory behaviour of certain properties with increasing thickness, e.g., energy and electron spillout change in discontinuous manner, due to quantum size effects [G. Materzanini, P. Saalfrank, and P. J. D. Lindan, Phys. Rev. B 63, 235405 (2001)]. Here, we demonstrate that oscillatory features arise also for hydrogen when chemisorbed on lead films. Besides stationary properties of the adsorbate, we concentrate on finite vibrational lifetimes of H-surface vibrations. As shown by AIMDEF, the damping via vibration-electron hole pair coupling dominates clearly over the vibration-phonon channel, in particular for high-frequency modes. Vibrational relaxation times are a characteristic function of layer thickness due to the oscillating behaviour of the embedding surface electronic density. Implications derived from AIMDEF for frictional many-atom dynamics, and physisorbed species will also be given.
Bruning, W.; Feil, D.
1992-01-01
An algorithm for calculating the scattering factors of atomic fragments in molecules as defined by the Stockholder recipe is presented. This method allows the calculation, from ab initio molecular wave functions, of structure factors including individual anisotropic atomic temperature factors. These
Energy Technology Data Exchange (ETDEWEB)
Scholes, G.D.; Fleming, G.R. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley National Lab., CA (United States). Physical Biosciences Div.; Gould, I.R. [Imperial Coll. of Science, Technology and Medicine, London (United Kingdom). Dept. of Chemistry; Cogdell, R.J. [Univ. of Glasgow (United Kingdom). Div. of Biochemistry and Molecular Biology
1999-04-01
The results of ab initio molecular orbital calculations of excited states and electronic couplings (for energy transfer) between the B800 and B850 bacteriochlorophyll a (Bchl) chromophores in the peripheral light-harvesting complex (LH2) of the purple photosynthetic bacterium Rhodopseudomonas acidophila are reported. Electronic couplings are estimated from supermolecule calculations of Bchl dimers using the Ci-singles methodology and 3-21G{sup *} or 6-31G{sup *} basis sets. A scheme for dissecting the coupling into contributions from the Coulombic coupling and the short-range coupling (i.e., dependent on interchromophore orbital overlap) is reported. B850 couplings are calculated to be [total (Coulombic + short)]: intrapolypeptide dimer 320 (265 + 55) cm{sup {minus}1} and interpolypeptide dimer 255 (195 + 60) cm{sup {minus}1} at the CIS/6-31G{sup *} level. These results differ significantly from those estimated using the point dipole approximation. The effect of including Mg ligands (His residues) and H-bonding residues (Trp and Tyr) is also investigated. The consequences for superradiance and energy transfer dynamics and mechanism are discussed.
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CalderIn, L [Research Computing and Cyberinfrastructure, The Pennsylvania State University, University Park, PA 16802 (United States); Gonzalez, L E; Gonzalez, D J, E-mail: david@liq1.fam.cie.uva.es [Departamento de Fisica Teorica, Facultad de Ciencias, Universidad de Valladolid, 47011 Valladolid (Spain)
2011-09-21
Fluid Hg undergoes a metal-nonmetal (M-NM) transition when expanded toward a density of around 9 g cm{sup -3}. We have performed ab initio molecular dynamics simulations for several thermodynamic states around the M-NM transition range and the associated static, dynamic and electronic properties have been analyzed. The calculated static structure shows a good agreement with the available experimental data. It is found that the volume expansion decreases the number of nearest neighbors from 10 (near the triple point) to around 8 at the M-NM transition region. Moreover, these neighbors are arranged into two subshells and the decrease in the number of neighbors occurs in the inner subshell. The calculated dynamic structure factors agree fairly well with their experimental counterparts obtained by inelastic x-ray scattering experiments, which display inelastic side peaks. The derived dispersion relation exhibits some positive dispersion for all the states, although its value around the M-NM transition region is not as marked as suggested by the experiment. We have also calculated the electronic density of states, which shows the appearance of a gap at a density of around 8.3 g cm{sup -3}. (paper)
Energy Technology Data Exchange (ETDEWEB)
Vazquez-Mayagoitia, Alvaro [ORNL; Fuentes-Cabrera, Miguel A [ORNL; Sumpter, Bobby G [ORNL; Luque, Javier [Universitat de Barcelona; Huertas, Oscar [Universitat de Barcelona; Orozco, Modesto [Institut de Recerca Biomedica, Parc Cientific de Barcelona, Barcelona, Spain; Felice, Rosa [INFM-CNR National Research Center S3; Brancolini, Giorgia [ORNL; Migliore, Agostino [University of Pennsylvania
2009-01-01
The structural, tautomeric, hydrogen-bonding, stacking and electronic properties of a seleno-derivative of thymine (T), denoted here as 4SeT and created by replacing O4 in T with Se, are investigated by means of ab initio computational techniques. The structural properties of T and 4SeT are very similar and the geometrical differences are mainly limited to the adjacent environment of the C-Se bond. The canonical keto form is the most stable tautomer, in gas phase and in aqueous solution, for both T and 4SeT. It is argued that the competition between two opposite trends, i.e. a decrease in the base-pairing ability and an increase of the stacking interaction upon incorporation of 4SeT into a duplex, likely explains the similar experimental melting points of a seleno-derivative duplex (Se-DNA) and its native counterpart. Interestingly, the underlying electronic structure shows that replacement of O4 with Se promotes a reduction in the HOMO-LUMO gap and an increase in inter-plane coupling, which suggests that Se-DNA could be potentially useful for nanodevice applications. This finding is further supported by the fact that transfer integrals between 4SeT---A stacked base pairs are larger than those determined for similarly stacked natural T---A pairs.
Chen, Hung-Cheng; Hsu, Chao-Ping
2005-12-29
To calculate electronic couplings for photoinduced electron transfer (ET) reactions, we propose and test the use of ab initio quantum chemistry calculation for excited states with the generalized Mulliken-Hush (GMH) method. Configuration-interaction singles (CIS) is proposed to model the locally excited (LE) and charge-transfer (CT) states. When the CT state couples with other high lying LE states, affecting coupling values, the image charge approximation (ICA), as a simple solvent model, can lower the energy of the CT state and decouple the undesired high-lying local excitations. We found that coupling strength is weakly dependent on many details of the solvent model, indicating the validity of the Condon approximation. Therefore, a trustworthy value can be obtained via this CIS-GMH scheme, with ICA used as a tool to improve and monitor the quality of the results. Systems we tested included a series of rigid, sigma-linked donor-bridge-acceptor compounds where "through-bond" coupling has been previously investigated, and a pair of molecules where "through-space" coupling was experimentally demonstrated. The calculated results agree well with experimentally inferred values in the coupling magnitudes (for both systems studied) and in the exponential distance dependence (for the through-bond series). Our results indicate that this new scheme can properly account for ET coupling arising from both through-bond and through-space mechanisms.
Grebenshchikov, Sergy Yu.
2013-06-01
The global potential energy surfaces of the first six singlet electronic states of CO2, 1—31A', and 1—31A″ are constructed using high level ab initio calculations. In linear molecule, they correspond to tilde{X}^1Σ _g^+, 11Δu, 1^1Σ _u^-, and 11Πg. The calculations accurately reproduce the known benchmarks for all states and establish missing benchmarks for future calculations. The calculated states strongly interact at avoided crossings and true intersections, both conical and glancing. Near degeneracies can be found for each pair of six states and many intersections involve more than two states. In particular, a fivefold intersection dominates the Franck-Condon zone for the ultraviolet excitation from the ground electronic state. The seam of this intersection traces out a closed loop. All states are diabatized, and a diabatic 5 × 5 potential matrix is constructed, which can be used in quantum mechanical calculations of the absorption spectrum of the five excited singlet valence states.
Grebenshchikov, Sergy Yu
2013-01-01
The global potential energy surfaces of the first six singlet electronic states of CO$_2$, 1---3$^1/!A'$ and 1---3$^1/!A"$ are constructed using high level ab initio calculations. In linear molecule, they correspond to $\\tilde{X}^1\\Sigma_g^+$, $1^1\\Delta_u$, $1^1\\Sigma_u^-$, and $1^1\\Pi_g$. The calculations accurately reproduce the known benchmarks for all states and establish missing benchmarks for future calculations. The calculated states strongly interact at avoided crossings and true intersections, both conical and glancing. Near degeneracies can be found for each pair of six states and many intersections involve more than two states. In particular, a fivefold intersection dominates the Franck-Condon zone for the ultraviolet excitation from the ground electronic state. The seam of this intersection traces out a closed loop. All states are diabatized, and a diabatic $5\\times 5$ potential matrix is constructed, which can be used in quantum mechanical calculations of the absorption spectrum of the five exci...
Keith, J. Brandon; Fennick, Jacob R.; Junkermeier, Chad E.; Nelson, Daniel R.; Lewis, James P.
2009-03-01
FIREBALL is an ab initio technique for fast local orbital simulations of nanotechnological, solid state, and biological systems. We have implemented a convenient interface for new users and software architects in the platform-independent Java language to access FIREBALL's unique and powerful capabilities. The graphical user interface can be run directly from a web server or from within a larger framework such as the Computational Science and Engineering Online (CSE-Online) environment or the Distributed Analysis of Neutron Scattering Experiments (DANSE) framework. We demonstrate its use for high-throughput electronic structure calculations and a multi-100 atom quantum molecular dynamics (MD) simulation. Program summaryProgram title: FireballUI Catalogue identifier: AECF_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECF_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.: 279 784 No. of bytes in distributed program, including test data, etc.: 12 836 145 Distribution format: tar.gz Programming language: Java Computer: PC and workstation Operating system: The GUI will run under Windows, Mac and Linux. Executables for Mac and Linux are included in the package. RAM: 512 MB Word size: 32 or 64 bits Classification: 4.14 Nature of problem: The set up and running of many simulations (all of the same type), from the command line, is a slow process. But most research quality codes, including the ab initio tight-binding code FIREBALL, are designed to run from the command line. The desire is to have a method for quickly and efficiently setting up and running a host of simulations. Solution method: We have created a graphical user interface for use with the FIREBALL code. Once the user has created the files containing the atomic coordinates for each system that they are
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.
Superconductivity and its mechanism in an ab initio model for electron-doped LaFeAsO.
Misawa, Takahiro; Imada, Masatoshi
2014-12-22
Two families of high-temperature superconductors whose critical temperatures are higher than 50 K are known. One are the copper oxides and the other are the iron-based superconductors. Comparisons of mechanisms between these two in terms of common ground as well as distinctions will greatly help in searching for higher T(c) superconductors. However, studies on mechanisms for the iron family based on first principles calculations are few. Here we first show that superconductivity emerges in the state-of-the-art numerical calculations for an ab initio multi-orbital model of an electron-doped iron-based superconductor LaFeAsO, in accordance with experimental observations. Then the mechanism of the superconductivity is identified as enhanced uniform density fluctuations by one-to-one correspondence with the instability towards inhomogeneity driven by first-order antiferromagnetic and nematic transitions. Despite many differences, certain common features with the copper oxides are also discovered in terms of the underlying orbital-selective Mottness found in the iron family.
Kirchhoff, F; Gillan, M J
1996-01-01
Ab initio molecular-dynamics simulations have been used to investigate the structure, dynamics and electronic properties of the liquid alloy Ag(1-x)Se(x) at 1350 K and at the three compositions x=0.33, 0.42 and 0.65. The calculations are based on density-functional theory in the local density approximation and on the pseudopotential plane-wave method. The reliability of the simulations is confirmed by detailed comparisons with very recent neutron diffraction results for the partial structure factors and radial distribution functions (RDF) of the stoichiometric liquid Ag2Se. The simulations show a dramatic change of the Se-Se RDF with increasing Se content. This change is due to the formation of Se clusters bound by covalent bonds, the Se-Se bond length being almost the same as in pure c-Se and l-Se. The clusters are predominantly chain-like, but for higher x a large fraction of 3-fold coordinated Se atoms is also found. It is shown that the equilibrium fractions of Se present as isolated atoms and in clusters...
Wang, Zi; Bevan, Kirk H.
2016-01-01
In the present work, we study the effects of the electronic relaxation of semicore levels on polaron activation energies and dynamics. Within the framework of adiabatic ab initio theory, we utilize both static transition state theory and molecular dynamics methods for an in-depth study of polaronic hopping in delithiated LiFePO4 (FePO4). Our results show that electronic relaxation of semicore states is significant in FePO4, resulting in a lower activation barrier and kinetics that is one to two orders faster compared to the result of calculations that do not incorporate semicore states. In general, the results suggest that the relaxation of states far below the Fermi energy could dramatically impact the ab initio polaronic barrier estimates for many transition metal oxides and phosphates.
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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.
Ferreira da Silva, F.; Lange, E.; Limão-Vieira, P.; Jones, N. C.; Hoffmann, S. V.; Hubin-Franskin, M.-J.; Delwiche, J.; Brunger, M. J.; Neves, R. F. C.; Lopes, M. C. A.; de Oliveira, E. M.; da Costa, R. F.; Varella, M. T. do N.; Bettega, M. H. F.; Blanco, F.; García, G.; Lima, M. A. P.; Jones, D. B.
2015-10-01
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.
Energy Technology Data Exchange (ETDEWEB)
Bylaska, Eric J.; Glaesemann, Kurt R.; Felmy, Andrew R.; Vasiliu, Monica; Dixon, David A.; Tratnyek, P. G.
2010-11-25
Electronic structure methods were used to calculate the gas-phase and aqueous phase reaction energies for reductive dechlorination (i.e. hydrogenolysis), reductive Beta-elimination, dehydrochlorination, and nucleophilic substitution by OH- of 1,2,3-trichloropropane. The thermochemical properties Delta Hof(298.15K), So(298.15K,1 bar), and Delta GS(298.15K, 1 bar) were calculated by using ab initio electronic structure calculations, isodesmic reactions schemes, gas-phase entropy estimates, and continuum solvation models for 1,2,3-trichloropropane and several likely metabolites. On the basis of these thermochemical estimates, together with a Fe(II)/Fe(III) chemical equilibrium model for natural reducing environments, all of the reactions studied were predicted to be very favorable in the standard state and under a wide range of pH conditions. The most favorable reaction was reductive Beta-elimination (Delta Gorxn ≈ -32 kcal/mol), followed closely by reductive dechlorination (Delta Gorxn ≈ -27 kcal/mol), dehydrochlorination (Delta Gorxn ≈ -27kcal/mol), and nucleophilic substitution by OH- (Delta Gorxn ≈ -25 kcal/mol). For both reduction reactions studied, it was found that the first electron-transfer step, yielding the intermediate CH2-CHCl-CH2Cl , and CH2Cl-CH-CH2Cl species, was not favorable in the standard state (Delta Gorxn ≈ +15 kcal/mol) and was predicted to occur only at relatively high pH values. This result suggests that reduction by natural attenuation is unlikely.
Maurer, Reinhard J; Batista, Victor S; Tully, John C
2016-01-01
Molecular adsorbates on metal surfaces exchange energy with substrate phonons and low-lying electron-hole pair excitations. In the limit of weak coupling, electron-hole pair excitations can be seen as exerting frictional forces on adsorbates that enhance energy transfer and facilitate vibrational relaxation or hot-electron mediated chemistry. We have recently reported on the relevance of tensorial properties of electronic friction [Phys. Rev. Lett. 116, 217601 (2016)] in dynamics at surfaces. Here we present the underlying implementation of tensorial electronic friction based on Kohn-Sham Density Functional Theory for condensed phase and cluster systems. Using local atomic-orbital basis sets, we calculate nonadiabatic coupling matrix elements and evaluate the full electronic friction tensor in the classical limit. Our approach is numerically stable and robust as shown by a detailed convergence analysis. We furthermore benchmark the accuracy of our approach by calculation of vibrational relaxation rates and li...
P-V Relation for Mercuric Calcogenides: Ab Initio Method
Directory of Open Access Journals (Sweden)
G. Misra
2011-01-01
Full Text Available Mercuric Calcogenides found many applications in electronic and optical devices as semiconducting materials. An equation of state provides useful information about the relationship between pressure (P, volume (V and temperature (T that helps to understand the behaviour of materials under the effect of high pressure and high temperature. The present paper sheds light on the electronic structure of Mercuric Calcogenides by simulating its electronic properties through ab initio method. This ab initio method is extended to derive the equation of state for Mercuric Calcogenides. The present equation of state has also been tested for the prediction of End Point. The computed results compare well with Quantum statistical data.
Ab initio investigations of the electronic structure of HeCH + and HeCH 2+
Hughes, Jason M.; von Nagy-Felsobuki, Ellak I.
1997-07-01
The 1A' and 3A″ electronic states of HeCH + and the 2A' ground electronic state of HeCH 2+ have been investigated using an all electron coupled cluster single, double and triple excitation [CCSD(T)] method coupled with an augmented correlation-consistent polarised core valence triple zeta basis set (aug-cc-pCVTZ). For the 1A' and 3A″ electronic states of HeCH +, the CCSD(T)a aug-cc-pCVTZ model yielded an optimised geometry of C s symmetry eith a { rCHe, rCH, θHCHe} structural parameters of {2.172 Å, 1.129 Å, 81.4°} and {1.675 Å, 1.121 Å, 101.4°} respectively. Moreover, this electronic model yielded the singlet state to be 26.3 kcal mol -1 lower in energy in energy when compared with the triplet state. For the 2A' ground electronic state of HeCH 2+ the optimised structural parameters were {1.388 Å, 1.253 Å, 110.5°}, respectively. The calculated harmonic frequencies for all these electronic states were found to be real.
Giant magnetoresistance An ab-initio description
Binder, J
2000-01-01
A new theoretical concept to study the microscopic origin of Giant Magnetoresistance (GMR) from first principles is presented. The method is based on ab-initio electronic structure calculations within the spin density functional theory using a Screened KORRINGA-KOHNROSTOKER method. Scattering at impurity atoms in the multilayers is described by means of a GREEN's-function method. The scattering potentials are calculated self-consistently. The transport properties are treated quasi-classically solving the BOLTZMANN equation including the electronic structure of the layered system and the anisotropic scattering. The solution of the BOLTZMANN equation is performed iteratively taking into account both scattering out and scattering in terms (vertex corrections). The method is applied to Co/Cu and Fe/Cr multilayers. Trends of scattering cross sections, residual resistivities and GMR ratios are discussed for various transition metal impurities at different positions in the Co/Cu or Fe/Cr multilayers. Furthermore the...
The new Resonating Valence Bond Method for ab-initio Electronic Simulations
Sorella, Sandro
2013-01-01
The Resonating Valence Bond theory of the chemical bond was introduced soon after the discovery of quantum mechanics and has contributed to explain the role of electron correlation within a particularly simple and intuitive approach where the chemical bond between two nearby atoms is described by one or more singlet electron pairs. In this chapter Pauling's resonating valence bond theory of the chemical bond is revisited within a new formulation, introduced by P.W. Anderson after the discovery of High-Tc superconductivity. It is shown that this intuitive picture of electron correlation becomes now practical and efficient, since it allows us to faithfully exploit the locality of the electron correlation, and to describe several new phases of matter, such as Mott insulators, High-Tc superconductors, and spin liquid phases.
Lawson, John W.; Bauschlicher, Charles W.; Daw, Murray
2011-01-01
Refractory materials such as metallic borides, often considered as ultra high temperature ceramics (UHTC), are characterized by high melting point, high hardness, and good chemical inertness. These materials have many applications which require high temperature materials that can operate with no or limited oxidation. Ab initio, first principles methods are the most accurate modeling approaches available and represent a parameter free description of the material based on the quantum mechanical equations. Using these methods, many of the intrinsic properties of these material can be obtained. We performed ab initio calculations based on density functional theory for the UHTC materials ZrB2 and HfB2. Computational results are presented for structural information (lattice constants, bond lengths, etc), electronic structure (bonding motifs, densities of states, band structure, etc), thermal quantities (phonon spectra, phonon densities of states, specific heat), as well as information about point defects such as vacancy and antisite formation energies.
Maurer, Reinhard J.; Askerka, Mikhail; Batista, Victor S.; Tully, John C.
2016-09-01
Molecular adsorbates on metal surfaces exchange energy with substrate phonons and low-lying electron-hole pair excitations. In the limit of weak coupling, electron-hole pair excitations can be seen as exerting frictional forces on adsorbates that enhance energy transfer and facilitate vibrational relaxation or hot-electron-mediated chemistry. We have recently reported on the relevance of tensorial properties of electronic friction [M. Askerka et al., Phys. Rev. Lett. 116, 217601 (2016), 10.1103/PhysRevLett.116.217601] in dynamics at surfaces. Here we present the underlying implementation of tensorial electronic friction based on Kohn-Sham density functional theory for condensed phase and cluster systems. Using local atomic-orbital basis sets, we calculate nonadiabatic coupling matrix elements and evaluate the full electronic friction tensor in the Markov limit. Our approach is numerically stable and robust, as shown by a detailed convergence analysis. We furthermore benchmark the accuracy of our approach by calculation of vibrational relaxation rates and lifetimes for a number of diatomic molecules at metal surfaces. We find friction-induced mode-coupling between neighboring CO adsorbates on Cu(100) in a c (2 ×2 ) overlayer to be important for understanding experimental findings.
Ab Initio Studies of Stratospheric Ozone Depletion Chemistry
Lee, Timothy J.; Head-Gordon, Martin; Langhoff, Stephen R. (Technical Monitor)
1995-01-01
An overview of the current understanding of ozone depletion chemistry, particularly with regards the formation of the so-called Antarctic ozone hole, will be presented together with an outline as to how ab initio quantum chemistry can be used to further our understanding of stratospheric chemistry. The ability of modern state-of-the art ab initio quantum chemical techniques to characterize reliably the gas-phase molecular structure, vibrational spectrum, electronic spectrum, and thermal stability of fluorine, chlorine, bromine and nitrogen oxide species will be demonstrated by presentation of some example studies. The ab initio results will be shown to be in excellent agreement with the available experimental data, and where the experimental data are either not known or are inconclusive, the theoretical results are shown to fill in the gaps and to resolve experimental controversies. In addition, ab initio studies in which the electronic spectra and the characterization of excited electronic states of halogen oxide species will also be presented. Again where available, the ab initio results are compared to experimental observations, and are used to aid in the interpretation of experimental studies.
Goumri-Said, Souraya
2010-08-01
In this Letter we investigate the electronic properties of the bulk and the nanofilm BeO in wurtzite structure. We performed a first-principles pseudo-potential method within the generalized gradient approximation. We will give more importance to the changes in band structure and density of states between the bulk structure and its derived nanofilms. The bonding characterization will be investigated via the analysis Mulliken population and charge density contours. It is found that the nanofilm retains the same properties as its bulk structure with slight changes in electronic properties and band structure which may offer some unusual transport properties. © 2010 Elsevier B.V. All rights reserved.
Electronic, vibrational and related properties of group IV metal oxides by ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Leite Alves, H.W. [Departamento de Ciencias Naturais, Universidade Federal de Sao Joao del Rei, C.P. 110, Sao Joao del Rei, MG 36301-160 (Brazil)], E-mail: hwlalves@ufsj.edu.br; Silva, C.C. [Departamento de Ciencias Naturais, Universidade Federal de Sao Joao del Rei, C.P. 110, Sao Joao del Rei, MG 36301-160 (Brazil); Lino, A.T. [Departamento de Fisica, Universidade Federal de Uberlandia, C.P. 593, Uberlandia, MG 38400-902 (Brazil); Borges, P.D. [Departamento de Engenharia de Telecomunicacoes, Uniao Educacional de Minas Gerais, Uberlandia, MG 38411-113 (Brazil); Scolfaro, L.M.R. [Instituto de Fisica, Universidade de Sao Paulo, C.P. 66318, Sao Paulo, SP 05315-970 (Brazil); Silva, E.F. da [Departamento de Fisica, Universidade Federal de Pernambuco, Cidade Universitaria, Recife, PE 50670-901 (Brazil)
2008-11-30
We present our theoretical results for the structural, electronic, vibrational and optical properties of MO{sub 2} (M = Sn, Zr, Hf and Ti) obtained by first-principles calculations. Relativistic effects are demonstrated to be important for a realistic description of the detailed structure of the electronic frequency-dependent dielectric function, as well as of the carrier effective masses. Based on our results, we found that the main contribution of the high values calculated for the oxides dielectric constants arises from the vibrational properties of these oxides, and the vibrational static dielectric constant values diminish with increasing pressure.
Ab initio investigation of the electronic properties of HgmTen clusters
Nanavati, Sachin; Kumar, Vijay; Pandey, Ravindra; Dixit, Ambesh
2014-03-01
Nanostructured HgTe quantum dots have attracted attention due to their potential applications in novel mid-infrared (3 - 5 μm) wavelength photodetectors and other optoelectronic applications. HgTe bulk material is a semimetal with bandgap ~ -0.3 eV, however at nanoscale, we observe drastic changes in the optical and electronic properties such as band gap opening, that makes it possible for engineering optoelectronic properties. We investigated the structural, optical, and electronic properties of HgmTen (m = n = 12, 13, 33, and 34) nanoparticles using density functional theory and the pseudopotential method within the generalized gradient approximation. The structures are relaxed to achieve the stable configurations and corresponding electronic properties are calculated. We investigated the density of states, energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), binding energy, and the Hg-Te bond length variation as a function of the cluster size. We will discuss the changes in the electronic structure and optical properties for these clusters with respect to the cluster size variation. The authors would like to thank C-DAC, Pune, India for the computational resources and MHRD, Gov. of India for financial support.
Ab-initio computations of electronic and transport properties of wurtzite aluminum nitride (w-AlN)
Energy Technology Data Exchange (ETDEWEB)
Nwigboji, Ifeanyi H.; Ejembi, John I.; Malozovsky, Yuriy; Khamala, Bethuel; Franklin, Lashounda; Zhao, Guanglin [Department of Physics, Southern University and A& M College, Baton Rouge, LA 70813 (United States); Ekuma, Chinedu E. [Department of Physics & Astronomy and Center for Computation and Technology, Louisiana State University, Baton Rouge, LA 70803 (United States); Bagayoko, Diola, E-mail: bagayoko@aol.com [Department of Physics, Southern University and A& M College, Baton Rouge, LA 70813 (United States)
2015-05-01
We report findings from several ab-initio, self-consistent calculations of electronic and transport properties of wurtzite aluminum nitride (w-AlN). Our calculations utilized a local density approximation (LDA) potential and the linear combination of Gaussian orbitals (LCGO). Unlike some other density functional theory (DFT) calculations, we employed the Bagayoko, Zhao, and Williams' method, enhanced by Ekuma and Franklin (BZW-EF). The BZW-EF method verifiably leads to the minima of the occupied energies; these minima, the low laying unoccupied energies, and related wave functions provide the most variationally and physically valid density functional theory (DFT) description of the ground states of materials under study. With multiple oxidation states of Al (Al{sup 3+} to Al) and the availability of N{sup 3−} to N, the BZW-EF method required several sets of self-consistent calculations with different ionic species as input. The binding energy for (Al{sup 3+}& N{sup 3−)} as input was 1.5 eV larger in magnitude than those for other input choices; the results discussed here are those from the calculation that led to the absolute minima of the occupied energies with this input. Our calculated, direct band gap for w-AlN, at the Γ point, is 6.28 eV, in excellent agreement with the 6.28 eV experimental value at 5K. We discuss the bands, total and partial densities of states, and calculated, effective masses. - Highlights: • LDA BZW-EF calculated band gap of w-AlN agrees well with experiment. • Features (widths & others) of the valence bands of w-AlN agree with experiment. • BZW-EF strictly adheres to the intrinsic requirements of DFT (and of LDA). • This adherence is the reason it outperforms DFT calculations not using it.
\\emph{Ab initio} Quantum Monte Carlo simulation of the warm dense electron gas
Dornheim, Tobias; Malone, Fionn; Schoof, Tim; Sjostrom, Travis; Foulkes, W M C; Bonitz, Michael
2016-01-01
Warm dense matter is one of the most active frontiers in plasma physics due to its relevance for dense astrophysical objects as well as for novel laboratory experiments in which matter is being strongly compressed e.g. by high-power lasers. Its description is theoretically very challenging as it contains correlated quantum electrons at finite temperature---a system that cannot be accurately modeled by standard analytical or ground state approaches. Recently several breakthroughs have been achieved in the field of fermionic quantum Monte Carlo simulations. First, it was shown that exact simulations of a finite model system ($30 \\dots 100$ electrons) is possible that avoid any simplifying approximations such as fixed nodes [Schoof {\\em et al.}, Phys. Rev. Lett. {\\bf 115}, 130402 (2015)]. Second, a novel way to accurately extrapolate these results to the thermodynamic limit was reported by Dornheim {\\em et al.} [Phys. Rev. Lett. {\\bf 117}, 156403 (2016)]. As a result, now thermodynamic results for the warm dense...
Ab-initio study of electronic structure and elastic properties of ZrC
Mund, H. S.; Ahuja, B. L.
2016-05-01
The electronic and elastic properties of ZrC have been investigated using the linear combination of atomic orbitals method within the framework of density functional theory. Different exchange-correlation functionals are taken into account within generalized gradient approximation. We have computed energy bands, density of states, elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, lattice parameters and pressure derivative of the bulk modulus by calculating ground state energy of the rock salt structure type ZrC.
Ab-initio calculations of electronic structure and optical properties of TiAl alloy
Hussain, Altaf; Sikandar Hayat, Sardar; Choudhry, M. A.
2011-05-01
The electronic structures and optical properties of TiAl intermetallic alloy system are studied by the first-principle orthogonalized linear combination of atomic orbitals method. Results on the band structure, total and partial density of states, localization index, effective atomic charges, and optical conductivity are presented and discussed in detail. Total density of states spectra reveal that (near the Fermi level) the majority of the contribution is from Ti-3d states. The effective charge calculations show an average charge transfer of 0.52 electrons from Ti to Al in primitive cell calculations of TiAl alloy. On the other hand, calculations using supercell approach reveal an average charge transfer of 0.48 electrons from Ti to Al. The localization index calculations, of primitive cell as well as of supercell, show the presence of relatively localized states even above the Fermi level for this alloy. The calculated optical conductivity spectra of TiAl alloy are rich in structures, showing the highest peak at 5.73 eV for supercell calculations. Calculations of the imaginary part of the linear dielectric function show a prominent peak at 5.71 eV and a plateau in the range 1.1-3.5 eV.
Extensive ab initio study of the electronic states of BSe radical including spin-orbit coupling
Liu, Siyuan; Zhai, Hongsheng; Liu, Yufang
2016-06-01
The internally contracted multi-reference configuration interaction method (MRCI) with Davidson modification and the Douglas-Kroll scalar relativistic correction has been used to calculate the BSe molecule at the level of aug-cc-pV5Z basis set. The calculated electronic states, including 9 doublet and 6 quartet Λ-S states, are correlated to the dissociation limit of B(2Pu) + Se(3Pg) and B(2Pu) + Se(1Dg). The Spin-orbit coupling (SOC) interaction is taken into account via the state interaction approach with the full Breit-Pauli Hamiltonian operator, which causes the entire 15 Λ-S states to split into 32 Ω states. This is the first time that the spin-orbit coupling calculation has been carried out on BSe. The potential energy curves of the Λ-S and Ω electronic states are depicted with the aid of the avoided crossing rule between electronic states of the same symmetry. The spectroscopic constants of the bound Λ-S and Ω states were determined, which are in good agreement with the experimental data. The transition dipole moments (TDMs) and the Franck-Condon factors (FCs) of the transitions from the low-lying bound Ω states A2Π(I)3/2, B2Π(I)1/2 and C2Δ(I)3/2 to the ground state X2Σ+1/2 have also been presented. Based on the previous calculations, the radiative lifetimes of the A2Π(I)3/2, B2Π(I)1/2 and C2Δ(I)3/2 were evaluated.
Electronic structure calculations of rare-earth intermetallic compound YAg using ab initio methods
Institute of Scientific and Technical Information of China (English)
(S).U(g)ur; G.U(g)ur; F.Soyalp; R.Ellialtio(g)lu
2009-01-01
The structural,elastic and electronic properties of YAg-B2(CsC1) were investigated using the first-principles calculations.The energy band structure and the density of states were studied in detail,including partial density of states (PDOS),in order to identify the character of each band.The structural parameters (lattice constant,bulk modulus,pressure derivative of bulk modulus) and elastic constants were also obtained.The results were consistent with the experimental data available in the literature,as well as other theoretical results.
Energy Technology Data Exchange (ETDEWEB)
Palmer, Michael H.; Guest, Martyn F
2003-07-01
The gas-phase VUV absorption spectrum of pyrazole, which we reported recently, has been further assigned in the light of multi-reference multi-root CI calculations, using basis sets of varying size up to quadruple zeta quality, and containing both valence and Rydberg type functions. A very intense VUV band centred near 7.8 eV appears to arise from the summation of three calculated bands of {pi}{pi}* character, of which the first and third are the most intense. The window resonance near the band maximum is ascribed to mutual annihilation of a Rydberg state and valence state, and a probable assignment is discussed. The electron energy loss (EEL) spectrum also obtained previously, showed low-lying triplet states at about 3.9 and 5.1 eV, respectively; the present computations suggest that two triplet ({sup 3}{pi}{pi}*) states lie within the 3.9 eV band, and identifies the species involved. The assignment of the UV-photoelectron spectrum has been reconsidered, but the identity of the first three IPs as {pi}{sub 3}<{pi}{sub 2}
Ab-initio study of structural and electronic properties of AlAs
Munjal, N.; Sharma, G.; Vyas, V.; Joshi, K. B.; Sharma, B. K.
2012-08-01
The structural properties, i.e. equilibrium lattice constant, transition pressure, bulk modulus and its pressure derivatives, together with electronic properties, i.e. energy bands, Compton profile and autocorrelation function, of AlAs are presented in this work. The linear combination of atomic orbitals (LCAO) method of the CRYSTAL code was applied considering the Perdew-Burke-Ernzerhof correlation energy functional and Becke's ansatz for the exchange. The total energy of AlAs as a function of primitive cell volume has also been calculated for the zincblende (B3), nickel arsenide (B8), sodium chloride (B1) and cesium chloride (B2) phases. Structural parameters of the B3, B8, B1 and B2 phases are determined. The calculated structural parameters are found to be in good agreement with the results of previous investigations. The spherically averaged theoretical values of Compton profile are in good agreement with an earlier measurement. The LCAO calculation shows an indirect band gap of 1.85 eV, in reasonable agreement with earlier data. On the basis of the equal-valence-electron-density Compton profile, it is found that AlAs is more ionic compared to AlSb.
Energy Technology Data Exchange (ETDEWEB)
Schiffmann, Florian; VandeVondele, Joost, E-mail: Joost.VandeVondele@mat.ethz.ch [Nanoscale Simulations, Department of Materials, ETH Zürich, Wolfgang-Pauli-Str. 27, CH-8093 Zürich (Switzerland)
2015-06-28
We present an improved preconditioning scheme for electronic structure calculations based on the orbital transformation method. First, a preconditioner is developed which includes information from the full Kohn-Sham matrix but avoids computationally demanding diagonalisation steps in its construction. This reduces the computational cost of its construction, eliminating a bottleneck in large scale simulations, while maintaining rapid convergence. In addition, a modified form of Hotelling’s iterative inversion is introduced to replace the exact inversion of the preconditioner matrix. This method is highly effective during molecular dynamics (MD), as the solution obtained in earlier MD steps is a suitable initial guess. Filtering small elements during sparse matrix multiplication leads to linear scaling inversion, while retaining robustness, already for relatively small systems. For system sizes ranging from a few hundred to a few thousand atoms, which are typical for many practical applications, the improvements to the algorithm lead to a 2-5 fold speedup per MD step.
Ab initio calculations of electronic structure of anatase TiO2
Institute of Scientific and Technical Information of China (English)
Chen Qiang; Cao Hong-Hong
2004-01-01
This paper presents the results of the self-consistent calculations on the electronic structure of anatase phase of TiO2. The calculations were performed using the full potential-linearized augmented plane wave method (FP-LAPW)in the framework of the density functional theory (DFT) with the generalized gradient approximation (GGA). The fully optimized structure, obtained by minimizing the total energy and atomic forces, is in good agreement with experiment.We also calculated the band structure and the density of states. In particular, the calculated band structure prefers an indirect transition between wlence and conduction bands of anatase TiO2, which may be helpful for clarifying the ambiguity in other theoretical works.
Ab initio electronic band structure study of III-VI layered semiconductors
Olguín, Daniel; Rubio-Ponce, Alberto; Cantarero, Andrés
2013-08-01
We present a total energy study of the electronic properties of the rhombohedral γ-InSe, hexagonal ɛ-GaSe, and monoclinic GaTe layered compounds. The calculations have been done using the full potential linear augmented plane wave method, including spin-orbit interaction. The calculated valence bands of the three compounds compare well with angle resolved photoemission measurements and a discussion of the small discrepancies found has been given. The present calculations are also compared with recent and previous band structure calculations available in the literature for the three compounds. Finally, in order to improve the calculated band gap value we have used the recently proposed modified Becke-Johnson correction for the exchange-correlation potential.
The electronic structure of MgO nanotubes. An ab initio quantum mechanical investigation.
El-Kelany, Khaled E; Ferrabone, Matteo; Rérat, Michel; Carbonnière, Philippe; Zicovich-Wilson, Claudio M; Dovesi, Roberto
2013-08-28
The structural, vibrational and response properties of the (n,0) and (m,m) MgO nanotubes are computed by using a Gaussian type basis set, a hybrid functional (B3LYP) and the CRYSTAL09 code. Tubes in the range 6 ≤ n ≤ 140 and 3 ≤ m ≤ 70 were considered, being n = 2 × m the number of MgO units in the unit cell (so, the maximum number of atoms is 280). Tubes are built by rolling up the fully relaxed 2-D conventional cell (2 MgO units, with oxygen atoms protruding from the Mg plane alternately up and down by 0.38 Å). The relative stability of the (n,0) with respect to the (m,m) family, the relaxation energy and equilibrium geometry, the band gap, the IR vibrational frequencies and intensities, and the electronic and ionic contributions to the polarizability are reported. All these properties are shown to converge smoothly to the monolayer values. Absence of negative vibrational frequencies confirms that the tubes have a stable structure. The parallel component of the polarizability α(∥) converges very rapidly to the monolayer value, whereas α(⊥) is still changing at n = 140; however, when extrapolated to very large n values, it coincides with the monolayer value to within 1%. The electronic contribution to α is in all cases (α(∥) and α(⊥); 6 ≤ n ≤ 140) smaller than the vibrational contribution by about a factor of three, at variance with respect to more covalent tubes such as the BN ones, for which the ratio between the two contributions is reversed.
Kafka, Graeme R; Masters, Sarah L; Rankin, David W H
2007-07-01
A new method of incorporating ab initio theoretical data dynamically into the gas-phase electron diffraction (GED) refinement process has been developed to aid the structure determination of large, sterically crowded molecules. This process involves calculating a set of differences between parameters that define the positions of peripheral atoms (usually hydrogen), as determined using molecular mechanics (MM), and those which use ab initio methods. The peripheral-atom positions are then updated continually during the GED refinement process, using MM, and the returned positions are modified using this set of differences to account for the differences between ab initio and MM methods, before being scaled back to the average parameters used to define them, as refined from experimental data. This allows the molecule to adopt a completely asymmetric structure if required, without being constrained by the MM parametrization, whereas the calculations can be performed on a practical time scale. The molecular structures of tri-tert-butylphosphine oxide and tri-tert-butylphosphine imide have been re-examined using this new technique, which we call SEMTEX (Structure Enhancement Methodology using Theory and EXperiment).
Ab initio study of long-range electron transfer between biphenyl anion radical and naphthalene
Institute of Scientific and Technical Information of China (English)
李象远; 肖顺清; 何福城
1999-01-01
After the separation of the donor, the aeceptor, and the σ-type bridge from the π-σ-π system, the geometries of biphenyl, biphenyl anion radical, naphthalene, and naphthalene anion radical are optimized, and then the reorganization energy for the intermolecular electron transfer （ET） at the levels of HF/4-31G and HF/DZP is calculated. The ET matrix elements of the self-exchange reactions of the π-σ-π systems have been calculated by means of both the direct calculation based on the variational principle, and the transition energy between the molecular orbitals at the linear coordinate R=0.5. For the cross reactions, the ET matrix element and the geometry of the transition state are determined by searching the minimum energy splitting △min along the reaction coordinate. In the evaluation of the solvent reorganization energy of the ET in solution, the Marcus’ two-sphere model has been invoked. A few of ET rate constants for the intramolecular ET reactions for the π-σ-π systems, which contain
Energy Technology Data Exchange (ETDEWEB)
Wu, Hai-Ying; Zhou, Ping; Han, Xiang-Yu [Jiaotong Univ., Chongqing (China). School of Science; Chen, Ya-Hong [North Univ. of China, Taiyuan (China). Scholl of Chemical Engineering and Environment; Liu, Zi-Jiang [Lanzhou City Univ. (China). Dept. of Physics
2014-08-15
The structural, electronic, and mechanical stability properties of magnesium sulfide in different phases are presented using the plane wave pseudopotential method within the generalized gradient approximation. Eight different phases such as rocksalt (B1), zincblende (B3), wurtzite (B4), nickel arsenide (B8), cesium chloride (B2), PH{sub 4}I-type (B11), FeSi-type (B28), and MnP-type (B31) are considered in great detail. The calculated ground-state properties of these phases are consistent with available experimental and theoretical data. It is found that MgS in the B1 and B8 phases are indirect band gap materials, the B3, B4, B11, B28, and B31 phases are all direct gap materials, while the B2 phase displays the metallic character. The B1, B3, B4, B8, B28, and B31 phases are mechanically stable at ambient conditions, but the B2 and B11 phases are mechanically unstable under zero pressure and zero temperature.
Kinetic Formulation of the Kohn-Sham Equations for ab initio Electronic Structure Calculations
Mendoza, M; Herrmann, H J
2013-01-01
We introduce a new approach to density functional theory based on kinetic theory, showing that the Kohn-Sham equations can be derived as a macroscopic limit of a suitable Boltzmann kinetic equation in the limit of small mean free path versus the typical scale of density gradients (Chapman-Enskog expansion). To derive the approach, we first write the Schr\\"odinger equation as a special case of a Boltzmann equation for a gas of quasi-particles, with the potential playing the role of an external source that generates and destroys particles, so as to drive the system towards the ground state. The ions are treated as classical particles, using the Born-Oppenheimer dynamics, or by imposing concurrent evolution with the electronic orbitals. In order to provide quantitative support to our approach, we implement a discrete (lattice) model and compute, the exchange and correlation energies of simple atoms, and the geometrical configuration of the methane molecule. Excellent agreement with values in the literature is fo...
Bylaska, Eric J; Glaesemann, Kurt R; Felmy, Andrew R; Vasiliu, Monica; Dixon, David A; Tratnyek, Paul G
2010-11-25
Electronic structure methods were used to calculate the gas and aqueous phase reaction energies for reductive dechlorination (i.e., hydrogenolysis), reductive β-elimination, dehydrochlorination, and nucleophilic substitution by OH− of 1,2,3-trichloropropane. The thermochemical properties ΔH(f)°(298.15 K), S°(298.15 K, 1 bar), and ΔG(S)(298.15 K, 1 bar) were calculated by using ab initio electronic structure calculations, isodesmic reactions schemes, gas-phase entropy estimates, and continuum solvation models for 1,2,3-trichloropropane and several likely degradation products: CH3−CHCl−CH2Cl, CH2Cl−CH2−CH2Cl, C•H2−CHCl−CH2Cl, CH2Cl−C•H−CH2Cl, CH2═CCl−CH2Cl, cis-CHCl═CH−CH2Cl, trans-CHCl═CH−CH2Cl, CH2═CH−CH2Cl, CH2Cl−CHCl−CH2OH, CH2Cl−CHOH−CH2Cl, CH2═CCl−CH2OH, CH2═COH−CH2Cl, cis-CHOH═CH−CH2Cl, trans-CHOH═CH−CH2Cl, CH(═O)−CH2−CH2Cl, and CH3−C(═O)−CH2Cl. On the basis of these thermochemical estimates, together with a Fe(II)/Fe(III) chemical equilibrium model for natural reducing environments, all of the reactions studied were predicted to be very favorable in the standard state and under a wide range of pH conditions. The most favorable reaction was reductive β-elimination (ΔG(rxn)° ≈ −32 kcal/mol), followed closely by reductive dechlorination (ΔG(rxn)° ≈ −27 kcal/mol), dehydrochlorination (ΔG(rxn)° ≈ −27 kcal/mol), and nucleophilic substitution by OH− (ΔG(rxn)° ≈ −25 kcal/mol). For both reduction reactions studied, it was found that the first electron-transfer step, yielding the intermediate C•H2−CHCl−CH2Cl and the CH2Cl−C•H−CH2Cl species, was not favorable in the standard state (ΔG(rxn)° ≈ +15 kcal/mol) and was predicted to occur only at relatively high pH values. This result suggests that reduction by natural attenuation is unlikely.
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.
Electronic Transport Properties of a Naphthopyran-Based Optical Molecular Switch:an ab initio Study
Institute of Scientific and Technical Information of China (English)
XIA Cai-Juan; LIU De-Sheng; ZHANG Ying-Tang
2011-01-01
The electronic transport properties of a. Naphthopyran-based molecular optical switch are investigated by using the nonequilibrium Green's Function formalism combined with first-principles density functional theory. The molecule that comprises the switch can convert between its open and closed forms upon photoexcitation. Theoretical results show that the current through the open form is significantly larger than that through the closed form, which is different from other optical switches based on ring-opening reactions of the molecular bridge. The maximum on-off ratio (about 90) can be obtained at 1.4 V. The physical origin of the switching behavior is interpreted based on the spatial distributions of molecular orbitals and the HOMO-LUMO gap. Our result shows that the naphthopyran-based molecule is a good candidate for optical molecular switches and will be useful in the near future.%@@ ronic transport properties of a naphthopyran-based molecular optical switch are investigated by using the nonequilibrium Green's function formalism combined with first-principles density functional theory.The molecule that comprises the switch can convert between its open and closed forms upon photoexcitation.Theoretical results show that the current through the open form is significantly larger than that through the closed form,which is different from other optical switches based on ring-opening reactions of the molecular bridge.The maximum on-off ratio(about 90)can be obtained at 1.4 V.The physical origin of the switching behavior is interpreted based on the spatial distributions of molecular orbitals and the HOMO-LUMO gap.Our result shows that the naphthopyran-based molecule is a good candidate for optical molecular switches and will be useful in the near future.
Ab Initio Study of the Electron Transfer in an Ionized Stacked Complex of Guanines
Cauët, Emilie; Liévin, Jacques
2009-08-01
The charge transfer process in an ionized stacking of two consecutive guanines (G5'G3')+ has been studied by means of state-averaged CASSCF/MRCI and RASSCF/RASPT2 calculations. The ground and two first excited states of the radical cation have been characterized, and the topology of the corresponding potential energy surfaces (PESs) has been studied as a function of all intermolecular geometrical parameters. The results demonstrate that the charge transfer process in (G5'G3')+ is governed by the avoiding crossing between the ground and first excited states of the complex. Relative translation motions of both guanines in their molecular planes are shown to lead to the charge migration between G5' and G3'. Five stationary points (three minima and two saddle points) have been characterized along the reaction path describing the passage of the positive charge from G5' to G3'. The global minimum on the PES is found to correspond to the charge configuration G5'+G3'. The existence of an intermediate minimum along the reaction path has been established, characterizing a structure where the positive charge is equally distributed between the two guanines. The calculated energy profile allowed us to determine the height of the potential energy barrier (7.33 kcal/mol) and to evaluate the electronic coupling at a geometry close to the avoiding crossing (3.6 kcal/mol). Test calculations showed that the topology of the ground state PES of the complex GG+ is qualitatively conserved upon optimization of the intramolecular geometrical parameters of the stationary points.
de Melo, Pedro Miguel M. C.; Marini, Andrea
2016-04-01
We present a full ab initio description of the coupled out-of-equilibrium dynamics of photons, phonons, and electrons. In the present approach, the quantized nature of the electromagnetic field as well as of the nuclear oscillations is fully taken into account. The result is a set of integrodifferential equations, written on the Keldysh contour, for the Green's functions of electrons, phonons, and photons where the different kinds of interactions are merged together. We then concentrate on the electronic dynamics in order to reduce the problem to a computationally feasible approach. By using the generalized Baym-Kadanoff ansatz and the completed collision approximation, we introduce a series of efficient but controllable approximations. In this way, we reduce all equations to a set of decoupled equations for the density matrix that describe all kinds of static and dynamical correlations. The final result is a coherent, general, and inclusive scheme to calculate several physical quantities: carrier dynamics, transient photoabsorption, and light emission, all of which include, at the same time, electron-electron, electron-phonon, and electron-photon interactions. We further discuss how all these observables can be easily calculated within the present scheme using a fully atomistic ab initio approach.
Energy Technology Data Exchange (ETDEWEB)
Genderen, E. van; Clabbers, M. T. B. [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Center for Cellular Imaging and NanoAnalytics (C-CINA), Biozentrum, University of Basel, CH-4058 Basel (Switzerland); Das, P. P. [Nanomegas SPRL, Boulevard Edmond Machtens 79, B 1080, Brussels (Belgium); Stewart, A. [Department of Physics and Energy, Materials and Surface Science Institute (MSSI), University of Limerick, Limerick (Ireland); Nederlof, I. [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Amsterdam Scientific Instruments, Postbus 41882, 1009 DB Amsterdam (Netherlands); Barentsen, K. C. [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Portillo, Q. [Nanomegas SPRL, Boulevard Edmond Machtens 79, B 1080, Brussels (Belgium); Centres Científics i Tecnològics de la Universitat de Barcelona, University of Barcelona, Carrer de Lluís Solé i Sabaris, 1-3, Barcelona (Spain); Pannu, N. S. [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Nicolopoulos, S. [Nanomegas SPRL, Boulevard Edmond Machtens 79, B 1080, Brussels (Belgium); Gruene, T., E-mail: tim.gruene@psi.ch [Biology and Chemistry, Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen (Switzerland); Abrahams, J. P., E-mail: tim.gruene@psi.ch [Biophysical Structural Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden (Netherlands); Center for Cellular Imaging and NanoAnalytics (C-CINA), Biozentrum, University of Basel, CH-4058 Basel (Switzerland); Biology and Chemistry, Laboratory of Biomolecular Research, Paul Scherrer Institute (PSI), 5232 Villigen (Switzerland)
2016-02-05
A specialized quantum area detector for electron diffraction studies makes it possible to solve the structure of small organic compound nanocrystals in non-cryo conditions by direct methods. Until recently, structure determination by transmission electron microscopy of beam-sensitive three-dimensional nanocrystals required electron diffraction tomography data collection at liquid-nitrogen temperature, in order to reduce radiation damage. Here it is shown that the novel Timepix detector combines a high dynamic range with a very high signal-to-noise ratio and single-electron sensitivity, enabling ab initio phasing of beam-sensitive organic compounds. Low-dose electron diffraction data (∼0.013 e{sup −} Å{sup −2} s{sup −1}) were collected at room temperature with the rotation method. It was ascertained that the data were of sufficient quality for structure solution using direct methods using software developed for X-ray crystallography (XDS, SHELX) and for electron crystallography (ADT3D/PETS, SIR2014)
Nishioka, Hirotaka; Ando, Koji
2011-05-28
By making use of an ab initio fragment-based electronic structure method, fragment molecular orbital-linear combination of MOs of the fragments (FMO-LCMO), developed by Tsuneyuki et al. [Chem. Phys. Lett. 476, 104 (2009)], we propose a novel approach to describe long-distance electron transfer (ET) in large system. The FMO-LCMO method produces one-electron Hamiltonian of whole system using the output of the FMO calculation with computational cost much lower than conventional all-electron calculations. Diagonalizing the FMO-LCMO Hamiltonian matrix, the molecular orbitals (MOs) of the whole system can be described by the LCMOs. In our approach, electronic coupling T(DA) of ET is calculated from the energy splitting of the frontier MOs of whole system or perturbation method in terms of the FMO-LCMO Hamiltonian matrix. Moreover, taking into account only the valence MOs of the fragments, we can considerably reduce computational cost to evaluate T(DA). Our approach was tested on four different kinds of model ET systems with non-covalent stacks of methane, non-covalent stacks of benzene, trans-alkanes, and alanine polypeptides as their bridge molecules, respectively. As a result, it reproduced reasonable T(DA) for all cases compared to the reference all-electron calculations. Furthermore, the tunneling pathway at fragment-based resolution was obtained from the tunneling current method with the FMO-LCMO Hamiltonian matrix.
Ab initio molecular dynamics simulation of laser melting of silicon
Silvestrelli, P.-L.; Alavi, A.; Parrinello, M.; Frenkel, D.
1996-01-01
The method of ab initio molecular dynamics, based on finite temperature density functional theory, is used to simulate laser heating of crystal silicon. We have found that a high concentration of excited electrons dramatically weakens the covalent bond. As a result, the system undergoes a melting tr
Ab-initio study of the electronic structure of sup 1 sup 9 F implanted in GaAs and GaN crystals
Park, J H; Cho, H S; Shin, Y N
1998-01-01
We have studied the nuclear quadrupole interaction of a fluorine atom implanted in gallium arsenide and gallium nitride cluster models using the ab-initio Hartree-Fock theory. For the three possible fluorine sites in GaAs and GaN, we have determined the location of the implanted fluorine atom by using a self-consistent calculation, the electric field gradient at the implanted atom, and the electronic structure. Good agreement is found with experimental data wherever they are available. Predictions are made for the implanted fluorine site associated with the total energy and the electric field gradient which are expected to be measurable by a variety of experimental techniques.
Energy Technology Data Exchange (ETDEWEB)
Benrekia, A.R., E-mail: benrekia.ahmed@yahoo.com [Faculty of Science and Technology, University of Medea (Algeria); Benkhettou, N. [Laboratoire des Materiaux Magnetiques, Faculte des Sciences, Universite Djillali Liabes de Sidi Bel Abbes (Algeria); Nassour, A. [Laboratoire de Cristallographie, Resonance Magnetique et Modelisations (CRM2, UMR CNRS 7036) Institut Jean Barriol, Nancy Universite BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-les-Nancy (France); Driz, M. [Applied Material Laboratory (AML), Electronics Department, University of Sidi bel Abbes (DZ 22000) (Algeria); Sahnoun, M. [Laboratoire de Physique Quantique de la Matiere et Modelisations Mathematique (LPQ3M), Faculty of Science and Technology,University of Mascara (Algeria); Lebegue, S. [Laboratoire de Cristallographie, Resonance Magnetique et Modelisations (CRM2, UMR CNRS 7036) Institut Jean Barriol, Nancy Universite BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-les-Nancy (France)
2012-07-01
We present first-principles VASP calculations of the structural, electronic, vibrational, and optical properties of paraelectric SrTiO{sub 3} and KTaO{sub 3}. The ab initio calculations are performed in the framework of density functional theory with different exchange-correlation potentials. Our calculated lattice parameters, elastic constants, and vibrational frequencies are found to be in good agreement with the available experimental values. Then, the bandstructures are calculated with the GW approximation, and the corresponding band gap is used to obtain the optical properties of SrTiO{sub 3} and KTaO{sub 3}.
Tayran, Ceren; Zhu, Zhen; Baldoni, Matteo; Selli, Daniele; Seifert, Gotthard; Tománek, David
2013-04-26
We use ab initio density-functional calculations to determine the interaction of a graphene monolayer with the Si(111) surface. We find that graphene forms strong bonds to the bare substrate and accommodates the 12% lattice mismatch by forming a wavy structure consisting of free-standing conductive ridges that are connected by ribbon-shaped regions of graphene, which bond covalently to the substrate. We perform quantum transport calculations for different geometries to study changes in the transport properties of graphene introduced by the wavy structure and bonding to the Si substrate. Our results suggest that wavy graphene combines high mobility along the ridges with efficient carrier injection into Si in the contact regions.
Shayesteh, Alireza; Alavi, S. Fatemeh; Rahman, Moloud; Gharib-Nezhad, Ehsan
2017-01-01
Ab initio potential energy curves have been calculated for the X2Σ+, A2Π, B2Σ+, 12Δ, E2Π and D2Σ+ states of CaH using the multi-reference configuration interaction method with large active space and basis sets. Transition dipole moments were calculated at Ca-H distances from 2.0 a0 to 14.0 a0, and excited state lifetimes were obtained. Our theoretical transition dipole moments can be combined with the available experimental data on the X2Σ+, A2Π and B2Σ+ states to calculate Einstein A coefficients for all rovibronic transitions of CaH appearing in solar and stellar spectra.
Tatemizo, N.; Imada, S.; Miura, Y.; Yamane, H.; Tanaka, K.
2017-03-01
The valence band (VB) structures of wurtzite AlCrN (Cr concentration: 0-17.1%), which show optical absorption in the ultraviolet-visible-infrared light region, were investigated via photoelectron yield spectroscopy (PYS), x-ray/ultraviolet photoelectron spectroscopy (XPS/UPS), and ab initio density of states (DOS) calculations. An obvious photoelectron emission threshold was observed ~5.3 eV from the vacuum level for AlCrN, whereas no emission was observed for AlN in the PYS spectra. Comparisons of XPS and UPS VB spectra and the calculated DOS imply that Cr 3d states are formed both at the top of the VB and in the AlN gap. These data suggest that Cr doping could be a viable option to produce new materials with relevant energy band structures for solar photoelectric conversion.
Kornobis, Karina; Wong, Bryan M; Lodowski, Piotr; Jaworska, Maria; Andruniów, Tadeusz; Rudd, Kenneth; Kozlowski, Pawel M; 10.1021/jp110914y
2011-01-01
Time-dependent density functional theory (TD-DFT) and correlated ab initio methods have been applied to the electronically excited states of vitamin B12 (cyanocobalamin or CNCbl). Different experimental techniques have been used to probe the excited states of CNCbl, revealing many issues that remain poorly understood from an electronic structure point of view. Due to its efficient scaling with size, TD-DFT emerges as one of the most practical tools that can be used to predict the electronic properties of these fairly complex molecules. However, the description of excited states is strongly dependent on the type of functional used in the calculations. In the present contribution, the choice of a proper functional for vitamin B12 was evaluated in terms of its agreement with both experimental results and correlated ab initio calculations. Three different functionals, i.e. B3LYP, BP86, and LC-BLYP, were tested. In addition, the effect of relative contributions of DFT and HF to the exchange-correlation functional ...
Institute of Scientific and Technical Information of China (English)
M. A. Hadi; M. A. Alam; M. Roknuzzaman; M. T. Nasir; A. K. M. A. Islam; S. H. Naqib
2015-01-01
The structural, elastic, and electronic properties of the very recently discovered ternary silicide superconductor, Li2IrSi3, are calculated using an ab-initio technique. We adopt the plane-wave pseudopotential approach within the frame-work of the first-principles density functional theory (DFT) implemented by the CASTEP code. The calculated structural parameters show reasonable agreement with the experimental results. The elastic moduli of this interesting material are calculated for the first time. The electronic band structure and electronic energy density of states indicate the strong cova-lent Ir–Si and Si–Si bonding, which leads to the formation of the rigid structure of Li2IrSi3. Strong covalency gives rise to a high Debye temperature in this system. We discuss the theoretical results in detail in this paper.
Ab initio calculation of tight-binding parameters
Energy Technology Data Exchange (ETDEWEB)
McMahan, A.K.; Klepeis, J.E.
1997-12-01
We calculate ab initio values of tight-binding parameters for the f- electron metal Ce and various phases of Si, from local-density functional one-electron Hamiltonian and overlap matrix elements. Our approach allows us to unambiguously test the validity of the common minimal basis and two-center approximations as well as to determine the degree of transferability of both nonorthogonal and orthogonal hopping parameters in the cases considered.
Discovering chemistry with an ab initio nanoreactor
Wang, Lee-Ping; Titov, Alexey; McGibbon, Robert; Liu, Fang; Pande, Vijay S.; Martínez, Todd J.
2014-01-01
Chemical understanding is driven by the experimental discovery of new compounds and reactivity, and is supported by theory and computation that provides detailed physical insight. While theoretical and computational studies have generally focused on specific processes or mechanistic hypotheses, recent methodological and computational advances harken the advent of their principal role in discovery. Here we report the development and application of the ab initio nanoreactor – a highly accelerat...
Highly scalable Ab initio genomic motif identification
Marchand, Benoit
2011-01-01
We present results of scaling an ab initio motif family identification system, Dragon Motif Finder (DMF), to 65,536 processor cores of IBM Blue Gene/P. DMF seeks groups of mutually similar polynucleotide patterns within a set of genomic sequences and builds various motif families from them. Such information is of relevance to many problems in life sciences. Prior attempts to scale such ab initio motif-finding algorithms achieved limited success. We solve the scalability issues using a combination of mixed-mode MPI-OpenMP parallel programming, master-slave work assignment, multi-level workload distribution, multi-level MPI collectives, and serial optimizations. While the scalability of our algorithm was excellent (94% parallel efficiency on 65,536 cores relative to 256 cores on a modest-size problem), the final speedup with respect to the original serial code exceeded 250,000 when serial optimizations are included. This enabled us to carry out many large-scale ab initio motiffinding simulations in a few hours while the original serial code would have needed decades of execution time. Copyright 2011 ACM.
Ab initio Bogoliubov coupled cluster theory
Signoracci, Angelo; Hagen, Gaute; Duguet, Thomas
2014-09-01
Coupled cluster (CC) theory has become a standard method in nuclear theory for realistic ab initio calculations of medium mass nuclei, but remains limited by its requirement of a Slater determinant reference state which reasonably approximates the nuclear system of interest. Extensions of the method, such as equation-of-motion CC, permit the calculation of nuclei with one or two nucleons added or removed from a doubly magic core, yet still only a few dozen nuclei are accessible with modern computational restrictions. In order to extend the applicability of ab initio methods to open-shell systems, the superfluid nature of nuclei must be taken into account. By utilizing Bogoliubov algebra and employing spontaneous symmetry breaking with respect to particle number conservation, superfluid systems can be treated by a single reference state. An ab initio theory to include correlations on top of a Bogoliubov reference state has been developed in the guise of standard CC theory. The formalism and first results of this Bogoliubov coupled cluster theory will be presented to demonstrate the applicability of the method.
Ab initio study on the electronic states and laser cooling of AlCl and AlBr
Rong, Yang; Bin, Tang; Tao, Gao
2016-04-01
We investigate whether AlCl and AlBr are promising candidates for laser cooling. We report new ab initio calculations on the ground state X1Σ+ and two low-lying states (A1Π and a3Π) of AlCl and AlBr. The calculated spectroscopic constants show good agreement with available theoretical and experimental results. We also obtain the permanent dipole moments (PDMs) curve at multi-reference configuration interaction (MRCI) level of theory. The transition properties of A1Π and a3Π states are predicted, including the transition dipole moments (TDMs), Franck-Condon factors (FCFs), radiative times and radiative width. The calculated radiative lifetimes are of the order of a nanosecond, implying that they are sufficiently short for rapid laser cooling. Both AlCl and AlBr have highly diagonally distributed FCFs which are crucial requirement for molecular laser cooling. The results demonstrate the feasibility of laser cooling AlCl and AlBr, and we propose laser cooling schemes for AlCl and AlBr.
Yan, Lingling; Qu, Yizhi; Liu, Chunhua; Wang, Jianguo; Buenker, Robert J
2012-03-28
An ab initio multireference single- and double-excitation configuration interaction (CI) study is carried out for the ground and excited electronic states of alkali-hydride cations (LiH(+), NaH(+), KH(+), RbH(+), and CsH(+)). For all alkali-metal atoms, the first inner-shell and valence electrons (nine active electrons, three for Li) are considered explicitly in the ab initio self-consistent-field and CI calculations. The adiabatic potential energy curves, radial and rotational couplings are calculated and presented. Short-range (∼3 a.u.) potential wells produced by the excitation of the inner-shell electrons are found. The depths of the inner potential wells are much greater than those of the outer wells for the CsH(+) system. The computed spectroscopic constants for the long-range potential well of the 2 (2)Σ(+) state are very close to the available theoretical and experimental data. The electronic states of alkali-hydrogen cations are also compared with each other, it is found that the positions of the potential wells shift to larger internuclear distances gradually, and the depths of these potential wells become greater with increasing alkali-metal atomic number. The relationships between structures of the radial coupling matrix elements and the avoiding crossings of the potential curves are analyzed. From NaH(+) to CsH(+), radial coupling matrix elements display more and more complex structures due to the gradual decrease of energy separations for avoided crossings. Finally, the behavior of some rotational couplings is also shown.
Energy Technology Data Exchange (ETDEWEB)
Soltani, N. [Department of Physics (Materials and Electroceramics Laboratory), Ferdowsi University of Mashhad (Iran, Islamic Republic of); Hosseini, S.M., E-mail: sma_hosseini@yahoo.co [Department of Physics (Materials and Electroceramics Laboratory), Ferdowsi University of Mashhad (Iran, Islamic Republic of); Kompany, A. [Department of Physics (Materials and Electroceramics Laboratory), Ferdowsi University of Mashhad (Iran, Islamic Republic of)
2009-11-15
We report nanoscale ab-initio calculations of the linear optical and electronic properties of LaCrO{sub 3} in nonmagnetic cubic and rhombohedral phases using the full potential linear augmented plane wave (FP-LAPW) method. In this work the generalized gradient approximation is used for exchange-correlation potential. The dielectric tensor is derived within random-phase approximation. We present results for the band structure, density of states, imaginary and real parts of dielectric tensor, electron energy loss spectroscopy, sum rules, reflectivity, refractive index and extinction coefficient. The regions of transparent, absorption and reflection are discussed. We are not aware of any published experimental or theoretical data for these phases, so our calculations can be used to cover this lack of data for these phases.
Energy Technology Data Exchange (ETDEWEB)
Jaiganesh, G., E-mail: jaiganesh@igcar.gov.in; Jaya, S. Mathi [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam - 603102 (India)
2015-06-24
The magnetism, structure and spin polarized electronic structure of Ti substituted MO (M = Mg, Ca, Sr) are studied using the ab-initio techniques within the framework of the density functional theory. Appropriately constructed supercell along with the full structural optimization of these cells is used for studying the influence of Ti substitution on the magnetism and electronic structure of these compounds. We find from our calculations that the Ti substituted MO compounds energetically favor magnetically ordered state. The Ti concentration is found to be important in deciding the magnetic order and we have observed antiferromagnetic order for the Ti concentration of 0.25. The Ti substituted MO compounds are thus an interesting class of materials that deserve further studies.
Ab Initio Calculations of Oxosulfatovanadates
DEFF Research Database (Denmark)
Frøberg, Torben; Johansen, Helge
1996-01-01
Restricted Hartree-Fock and multi-configurational self-consistent-field calculations together with secondorder perturbation theory have been used to study the geometry, the electron density, and the electronicspectrum of (VO2SO4)-. A bidentate sulphate attachment to vanadium was found to be stable...
Ab initio potential for solids
DEFF Research Database (Denmark)
Chetty, N.; Stokbro, Kurt; Jacobsen, Karsten Wedel;
1992-01-01
A total-energy theory for a solid is presented. It is based on density-functional theory and consists of a succession of approximations. At the most accurate level, the theory consists of a systematic derivation of an ansatz for the electron density which is best suited for the Harris functional....
Energy Technology Data Exchange (ETDEWEB)
Kubas, Adam; Blumberger, Jochen, E-mail: j.blumberger@ucl.ac.uk [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Hoffmann, Felix [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, Universitätsstr. 150, 44801 Bochum (Germany); Heck, Alexander; Elstner, Marcus [Institute of Physical Chemistry, Karlsruhe Institute of Technology, Fritz-Haber-Weg 6, 76131 Karlsruhe (Germany); Oberhofer, Harald [Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85747 Garching (Germany)
2014-03-14
We introduce a database (HAB11) of electronic coupling matrix elements (H{sub ab}) for electron transfer in 11 π-conjugated organic homo-dimer cations. High-level ab inito calculations at the multireference configuration interaction MRCI+Q level of theory, n-electron valence state perturbation theory NEVPT2, and (spin-component scaled) approximate coupled cluster model (SCS)-CC2 are reported for this database to assess the performance of three DFT methods of decreasing computational cost, including constrained density functional theory (CDFT), fragment-orbital DFT (FODFT), and self-consistent charge density functional tight-binding (FODFTB). We find that the CDFT approach in combination with a modified PBE functional containing 50% Hartree-Fock exchange gives best results for absolute H{sub ab} values (mean relative unsigned error = 5.3%) and exponential distance decay constants β (4.3%). CDFT in combination with pure PBE overestimates couplings by 38.7% due to a too diffuse excess charge distribution, whereas the economic FODFT and highly cost-effective FODFTB methods underestimate couplings by 37.6% and 42.4%, respectively, due to neglect of interaction between donor and acceptor. The errors are systematic, however, and can be significantly reduced by applying a uniform scaling factor for each method. Applications to dimers outside the database, specifically rotated thiophene dimers and larger acenes up to pentacene, suggests that the same scaling procedure significantly improves the FODFT and FODFTB results for larger π-conjugated systems relevant to organic semiconductors and DNA.
Accurate ab initio spin densities
Boguslawski, Katharina; Legeza, Örs; Reiher, Markus
2012-01-01
We present an approach for the calculation of spin density distributions for molecules that require very large active spaces for a qualitatively correct description of their electronic structure. Our approach is based on the density-matrix renormalization group (DMRG) algorithm to calculate the spin density matrix elements as basic quantity for the spatially resolved spin density distribution. The spin density matrix elements are directly determined from the second-quantized elementary operators optimized by the DMRG algorithm. As an analytic convergence criterion for the spin density distribution, we employ our recently developed sampling-reconstruction scheme [J. Chem. Phys. 2011, 134, 224101] to build an accurate complete-active-space configuration-interaction (CASCI) wave function from the optimized matrix product states. The spin density matrix elements can then also be determined as an expectation value employing the reconstructed wave function expansion. Furthermore, the explicit reconstruction of a CA...
Thermochemical data for CVD modeling from ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Ho, P. [Sandia National Labs., Albuquerque, NM (United States); Melius, C.F. [Sandia National Labs., Livermore, CA (United States)
1993-12-31
Ab initio electronic-structure calculations are combined with empirical bond-additivity corrections to yield thermochemical properties of gas-phase molecules. A self-consistent set of heats of formation for molecules in the Si-H, Si-H-Cl, Si-H-F, Si-N-H and Si-N-H-F systems is presented, along with preliminary values for some Si-O-C-H species.
Energy Technology Data Exchange (ETDEWEB)
Ramos de Debiaggi, S., E-mail: sbramos@yahoo.com [Facultad de Ingenieria, Universidad Nacional del Comahue, Buenos Aires 1400, (8300) Neuquen (Argentina); CONICET (Argentina); Cabeza, G.F. [CONICET (Argentina); Dpto. de Fisica, Universidad Nacional del Sur, Bahia Blanca (Argentina); Toro, C. Deluque [Facultad de Ingenieria, Universidad Nacional del Comahue, Buenos Aires 1400, (8300) Neuquen (Argentina); Monti, A.M. [CNEA e Instituto Sabato (Univ. Nac. de San Martin/CNEA), Centro Atomico Constituyentes, Avda. General Paz 1499, B1650KNA, San Martin, Buenos Aires (Argentina); Sommadossi, S. [Facultad de Ingenieria, Universidad Nacional del Comahue, Buenos Aires 1400, (8300) Neuquen (Argentina); CONICET (Argentina); Guillermet, A. Fernandez [CONICET (Argentina); Centro Atomico Bariloche e Instituto Balseiro, Avda. Bustillo 9500, (8400) Bariloche (Argentina)
2011-02-17
Research highlights: > Cu{sub 10}In{sub 7} and Cu{sub 11}In{sub 9} are thermodynamically stable with respect to elements at 0 K. > Cu{sub 10}In{sub 7} phase is more stable than the modelled Cu{sub 11}In{sub 9} compound by only 0.92 kJ/mol. > The present ab initio results reproduce very well the available structural data. > Similar DOS for both phases, the most prominent bonding band comes from Cu-d states. > Enhanced relative thermodynamic stability is predicted for phases with 40-45 at.% In. - Abstract: The physico-chemical properties of the intermetallic phases in the Cu-In system have been a matter of considerable theoretical and experimental interest in connection with, i.a., the application of In-Sn alloys as lead-free micro-soldering alloys. Recently, a new binary compound with the chemical formula Cu{sub 10}In{sub 7} has been detected in a study of the {eta}-phase field. The structure of the Cu{sub 10}In{sub 7} phase has been determined as closely related to that of the Cu{sub 11}In{sub 9} compound occurring in the phase diagram, but no experimental or theoretical information on its electronic structure, thermodynamic and equation-of-state properties has yet been reported. In the present work we report the lattice parameters, bulk modulus, energy of formation from the constituent elements and the electronic structure of the new phase, calculated by applying an ab initio density-functional-theory method. Our calculation technique uses the projector augmented wave potentials and the exchange-correlation functions of Perdew and Wang in the generalized gradient approximation. The present results for the Cu{sub 10}In{sub 7} phase are compared with the experimental data available, and with the trends in structural and thermodynamic properties emerging from ab initio calculations also performed in the present study for various structurally related and neighboring compounds in the Cu-In phase diagram, viz., the ideal B8{sub 2}-Cu{sub 2}In, B8{sub 1}-CuIn, B8{sub 2
Directory of Open Access Journals (Sweden)
Wagner B. De Almeida
2000-10-01
Full Text Available The determination of the molecular structure of molecules is of fundamental importance in chemistry. X-rays and electron diffraction methods constitute in important tools for the elucidation of the molecular structure of systems in the solid state and gas phase, respectively. The use of quantum mechanical molecular orbital ab initio methods offer an alternative for conformational analysis studies. Comparison between theoretical results and those obtained experimentally in the gas phase can make a significant contribution for an unambiguous determination of the geometrical parameters. In this article the determination of the molecular structure of the cyclooctane molecule by electron diffraction in the gas phase and ab initio calculations will be addressed, providing an example of a comparative analysis of theoretical and experimental predictions.
Le Page, Y
1992-04-01
A new method for the ab initio derivation of Buerger-reduced primitive cell parameters from coordinate measurements of spots on single convergent-beam electron diffraction (CBED) patterns is described, which does not involve trial-and-error. The pattern can be taken along any zone axis, and misorientations of the crystallite by as much as a few degrees are taken into account without loss of accuracy. This derivation of cell parameters by least-squares analysis of the measurements has been automated in a program called NRCBED. Present accuracy is about 1% on lengths and 2 degrees on angles, but could be significantly improved by modelling projector lens aberrations, or by using a microscope without a projector lens. With present technology, it is possible to obtain a CBED pattern and a semi-quantitative energy-dispersive X-ray (EDX) analysis simultaneously from a single microcrystal a few hundred Angströms across. It becomes therefore possible to identify the material of the crystal on a single CBED pattern: a cell parameter database for known compounds is searched with the primitive cell parameters obtained in the above way, and with a mask describing the EDX results qualitatively. Feasibility is demonstrated on a crystallite of CeO2 500 Angströms across. With this new approach, trial-and-error should disappear from the solution of other long-standing problems: interpretation of X-ray powder patterns for new compounds in the presence of impurity lines, or in the case of multiple phases should become straight-forward.
High Level Ab Initio Kinetics as a Tool for Astrochemistry
Klippenstein, Stephen
2015-05-01
We will survey the application of ab initio theoretical kinetics to reactions of importance to astrochemistry. Illustrative examples will be taken from our calculations for (i) interstellar chemistry, (ii) Titan's atmospheric chemistry, and (iii) the chemistry of extrasolar giant planets. The accuracy of various aspects of the calculations will be summarized including (i) the underlying ab initio electronic structure calculations, (ii) the treatment of the high pressure recombination process, and (iii) the treatment of the pressure dependence of the kinetics. The applications will consider the chemistry of phosphorous on giant planets, the kinetics of water dimerization, the chemistry of nitrogen on Titan's atmosphere, as well as various reactions of interstellar chemistry interest such as the recombination of OH with H, and O(3P) reacting with C2H5, CH2, and CCS. Chemical Sciences and Engineering Division.
Long, Run; English, Niall J; Prezhdo, Oleg V
2014-09-01
TiO2 sensitized with quantum dots (QDs) gives efficient photovoltaic and photocatalytic systems due to high stability and large absorption cross sections of QDs and rapid photoinduced charge separation at the interface. The yields of the light-induced processes are limited by electron-hole recombination that also occurs at the interface. We combine ab initio nonadiabatic molecular dynamics with analytic theory to investigate the experimentally studied charge recombination at the PbSe QD-TiO2 interface. The time-domain atomistic simulation directly mimics the laser experiment and generates important details of the recombination mechanism. The process occurs due to coupling of the electronic subsystem to polar optical modes of the TiO2 surface. The inelastic electron-phonon scattering happens on a picosecond time scale, while the elastic scattering takes 40 fs. Counter to expectations, the donor-acceptor bonding strengthens at an elevated temperature. An analytic theory extends the simulation results to larger QDs and longer QD-TiO2 bridges. It shows that the electron-hole recombination rate decreases significantly for longer bridges and larger dots and that the main effect arises due to reduced donor-acceptor coupling rather than changes in the donor-acceptor energy gap. The study indicates that by varying QD size or ligands one can reduce charge losses while still maintaining efficient charge separation, providing design principles for optimizing solar cell design and increasing photon-to-electron conversion efficiencies.
Energy Technology Data Exchange (ETDEWEB)
Ilyasov, V.V., E-mail: viily@mail.ru; Pham, Khang D., E-mail: dinhkhang307@gmail.com; Holodova, O.M.; Ershov, I.V., E-mail: thijd@mail.ru
2015-10-01
We have performed ab initio simulation of oxygen atom adsorption on TiC(0 0 1) laser-reconstructed surface. Relaxed atomic structures of the O/Ti{sub x}C{sub y}(0 0 1) surface observed upon thermal impact have been studied. DFT calculations of their thermodynamic, electronic, and elastic properties have been carried out. For the first time we have established the bond length and adsorption energy for various reconstructions of the O/Ti{sub x}C{sub y}(0 0 1) surface atomic structure. We have examined the effects of the oxygen adatom upon the band and electron spectra of the O/TiC(0 0 1) surface in its various reconstructions. For the first time we have established a correlation between the energy level of flat bands (−5.4 eV and −5.8 eV) responsible for the doublet of singular peaks of partial densities of oxygen 2p electrons, and the adsorption energy of oxygen atom in non-stoichiometric O/TiC{sub y}(0 0 1) systems. Effective charges of titanium and carbon atoms surrounding the oxygen adatom in various reconstructions have been identified. We have established charge transfer from titanium atom to oxygen and carbon atoms determined by the reconstruction of local atomic and electron structures which correlate with atomic electronegativity values and chemisorption processes. Potential mechanisms for laser nanostructuring of titanium carbide surface have been suggested.
Ab Initio Nuclear Structure and Reaction Calculations for Rare Isotopes
Energy Technology Data Exchange (ETDEWEB)
Draayer, Jerry P. [Louisiana State Univ., Baton Rouge, LA (United States)
2014-09-28
We have developed a novel ab initio symmetry-adapted no-core shell model (SA-NCSM), which has opened the intermediate-mass region for ab initio investigations, thereby providing an opportunity for first-principle symmetry-guided applications to nuclear structure and reactions for nuclear isotopes from the lightest p-shell systems to intermediate-mass nuclei. This includes short-lived proton-rich nuclei on the path of X-ray burst nucleosynthesis and rare neutron-rich isotopes to be produced by the Facility for Rare Isotope Beams (FRIB). We have provided ab initio descriptions of high accuracy for low-lying (including collectivity-driven) states of isotopes of Li, He, Be, C, O, Ne, Mg, Al, and Si, and studied related strong- and weak-interaction driven reactions that are important, in astrophysics, for further understanding stellar evolution, X-ray bursts and triggering of s, p, and rp processes, and in applied physics, for electron and neutrino-nucleus scattering experiments as well as for fusion ignition at the National Ignition Facility (NIF).
Ab initio multiple cloning algorithm for quantum nonadiabatic molecular dynamics.
Makhov, Dmitry V; Glover, William J; Martinez, Todd J; Shalashilin, Dmitrii V
2014-08-07
We present a new algorithm for ab initio quantum nonadiabatic molecular dynamics that combines the best features of ab initio Multiple Spawning (AIMS) and Multiconfigurational Ehrenfest (MCE) methods. In this new method, ab initio multiple cloning (AIMC), the individual trajectory basis functions (TBFs) follow Ehrenfest equations of motion (as in MCE). However, the basis set is expanded (as in AIMS) when these TBFs become sufficiently mixed, preventing prolonged evolution on an averaged potential energy surface. We refer to the expansion of the basis set as "cloning," in analogy to the "spawning" procedure in AIMS. This synthesis of AIMS and MCE allows us to leverage the benefits of mean-field evolution during periods of strong nonadiabatic coupling while simultaneously avoiding mean-field artifacts in Ehrenfest dynamics. We explore the use of time-displaced basis sets, "trains," as a means of expanding the basis set for little cost. We also introduce a new bra-ket averaged Taylor expansion (BAT) to approximate the necessary potential energy and nonadiabatic coupling matrix elements. The BAT approximation avoids the necessity of computing electronic structure information at intermediate points between TBFs, as is usually done in saddle-point approximations used in AIMS. The efficiency of AIMC is demonstrated on the nonradiative decay of the first excited state of ethylene. The AIMC method has been implemented within the AIMS-MOLPRO package, which was extended to include Ehrenfest basis functions.
A highly accurate ab initio potential energy surface for methane
Owens, Alec; Yurchenko, Sergei N.; Yachmenev, Andrey; Tennyson, Jonathan; Thiel, Walter
2016-09-01
A new nine-dimensional potential energy surface (PES) for methane has been generated using state-of-the-art ab initio theory. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit and incorporates a range of higher-level additive energy corrections. These include core-valence electron correlation, higher-order coupled cluster terms beyond perturbative triples, scalar relativistic effects, and the diagonal Born-Oppenheimer correction. Sub-wavenumber accuracy is achieved for the majority of experimentally known vibrational energy levels with the four fundamentals of 12CH4 reproduced with a root-mean-square error of 0.70 cm-1. The computed ab initio equilibrium C-H bond length is in excellent agreement with previous values despite pure rotational energies displaying minor systematic errors as J (rotational excitation) increases. It is shown that these errors can be significantly reduced by adjusting the equilibrium geometry. The PES represents the most accurate ab initio surface to date and will serve as a good starting point for empirical refinement.
Ab initio multiple cloning algorithm for quantum nonadiabatic molecular dynamics
Energy Technology Data Exchange (ETDEWEB)
Makhov, Dmitry V.; Shalashilin, Dmitrii V. [Department of Chemistry, University of Leeds, Leeds LS2 9JT (United Kingdom); Glover, William J.; Martinez, Todd J. [Department of Chemistry and The PULSE Institute, Stanford University, Stanford, California 94305, USA and SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States)
2014-08-07
We present a new algorithm for ab initio quantum nonadiabatic molecular dynamics that combines the best features of ab initio Multiple Spawning (AIMS) and Multiconfigurational Ehrenfest (MCE) methods. In this new method, ab initio multiple cloning (AIMC), the individual trajectory basis functions (TBFs) follow Ehrenfest equations of motion (as in MCE). However, the basis set is expanded (as in AIMS) when these TBFs become sufficiently mixed, preventing prolonged evolution on an averaged potential energy surface. We refer to the expansion of the basis set as “cloning,” in analogy to the “spawning” procedure in AIMS. This synthesis of AIMS and MCE allows us to leverage the benefits of mean-field evolution during periods of strong nonadiabatic coupling while simultaneously avoiding mean-field artifacts in Ehrenfest dynamics. We explore the use of time-displaced basis sets, “trains,” as a means of expanding the basis set for little cost. We also introduce a new bra-ket averaged Taylor expansion (BAT) to approximate the necessary potential energy and nonadiabatic coupling matrix elements. The BAT approximation avoids the necessity of computing electronic structure information at intermediate points between TBFs, as is usually done in saddle-point approximations used in AIMS. The efficiency of AIMC is demonstrated on the nonradiative decay of the first excited state of ethylene. The AIMC method has been implemented within the AIMS-MOLPRO package, which was extended to include Ehrenfest basis functions.
Ab initio path integral ring polymer molecular dynamics: Vibrational spectra of molecules
Shiga, Motoyuki; Nakayama, Akira
2008-01-01
The path integral ring polymer molecular dynamics method is combined with 'on-the-fly' ab initio electronic structure calculations and applied to vibrational spectra of small molecules, LiH and H 2O, at the room temperature. The results are compared with those of the numerically exact solution and ab initio path integral centroid molecular dynamics calculation. The peak positions in the calculated spectra are found to be reasonable, showing the red-shift due to potential anharmonicity. This unification enables the investigation of real-time quantum dynamics of chemically complex molecular systems on the ab initio Born-Oppenheimer potential energy surface.
Energy Technology Data Exchange (ETDEWEB)
Ramos de Debiaggi, S., E-mail: sbramos@yahoo.com [Facultad de Ingeniería, Universidad Nacional del Comahue, Buenos Aires 1400, 8300 Neuquén (Argentina); CONICET (Argentina); Deluque Toro, C. [Facultad de Ingeniería, Universidad Nacional del Comahue, Buenos Aires 1400, 8300 Neuquén (Argentina); Cabeza, G.F. [CONICET (Argentina); Dpto. de Física, Universidad Nacional del Sur, Alem 1253, 8000 Bahía Blanca (Argentina); Fernández Guillermet, A. [CONICET (Argentina); Centro Atómico Bariloche e Instituto Balseiro, Avda. Bustillo 9500, 8400 Bariloche (Argentina)
2013-11-05
Graphical abstract: -- Highlights: •A DFT study of Ni–In and Ni–Sn compounds in Ni–In–Sn soldering alloys is reported. •Cohesive, electronic structure, and thermodynamic stability trends are established. •Phase-stabilities at low T are well reproduced by the 0 K thermodynamic values. •Available structural and equation-of-state data are satisfactorily accounted for. •Ab initio and CALPHAD data of hypothetical phases involved in sublattice models are compared. -- Abstract: A comprehensive study of the structural, cohesive and electronic properties of several stable, metastable and non-stable intermetallic phases (IPs) of the Ni–In and Ni–Sn systems have been performed by ab initio density-funcional-theory (DFT) methods. Using the projector augmented wave method we have performed systematic spin polarized calculations with the exchange and correlation functions of Perdew and Wang in the generalized gradient approximation (GGA), as well as those by Ceperley and Alder in the local-density-approximation (LDA). Structural properties, the energy-of-formation (EOF) from the elements and the cohesive properties of the various phases have been established by minimizing the internal structural parameters. We present trends at 0 K in the composition dependence of the molar volumen, bulk modulus and its pressure derivative, electronic density of states, magnetic moments and the EOF of several stable and metastable IPs reported in the Ni–In and Ni–Sn systems as well as various non-stable (hypothetical) compounds which are relevant in connection with the thermodynamic analysis of the Ni–In and Ni–Sn systems using Gibbs energy models and the so-called CALPHAD techniques. The results are compared with the available experimental data and with previously reported theoretical results. The present study of the thermodynamic and cohesive properties of Ni–In/Sn intermetallic phases should contribute to the understanding of the phase-stability systematics in
Li, Junjie; Li, Xiaohu; Iyengar, Srinivasan S
2014-06-10
We discuss a multiconfigurational treatment of the "on-the-fly" electronic structure within the quantum wavepacket ab initio molecular dynamics (QWAIMD) method for coupled treatment of quantum nuclear effects with electronic structural effects. Here, multiple single-particle electronic density matrices are simultaneously propagated with a quantum nuclear wavepacket and other classical nuclear degrees of freedom. The multiple density matrices are coupled through a nonorthogonal configuration interaction (NOCI) procedure to construct the instantaneous potential surface. An adaptive-mesh-guided set of basis functions composed of Gaussian primitives are used to simplify the electronic structure calculations. Specifically, with the replacement of the atom-centered basis functions positioned on the centers of the quantum-mechanically treated nuclei by a mesh-guided band of basis functions, the two-electron integrals used to compute the electronic structure potential surface become independent of the quantum nuclear variable and hence reusable along the entire Cartesian grid representing the quantum nuclear coordinates. This reduces the computational complexity involved in obtaining a potential surface and facilitates the interpretation of the individual density matrices as representative diabatic states. The parametric nuclear position dependence of the diabatic states is evaluated at the initial time-step using a Shannon-entropy-based sampling function that depends on an approximation to the quantum nuclear wavepacket and the potential surface. This development is meant as a precursor to an on-the-fly fully multireference electronic structure procedure embedded, on-the-fly, within a quantum nuclear dynamics formalism. We benchmark the current development by computing structural, dynamic, and spectroscopic features for a series of bihalide hydrogen-bonded systems: FHF(-), ClHCl(-), BrHBr(-), and BrHCl(-). We find that the donor-acceptor structural features are in good
Discovering chemistry with an ab initio nanoreactor
Wang, Lee-Ping; Titov, Alexey; McGibbon, Robert; Liu, Fang; Pande, Vijay S.; Martínez, Todd J.
2014-12-01
Chemical understanding is driven by the experimental discovery of new compounds and reactivity, and is supported by theory and computation that provide detailed physical insight. Although theoretical and computational studies have generally focused on specific processes or mechanistic hypotheses, recent methodological and computational advances harken the advent of their principal role in discovery. Here we report the development and application of the ab initio nanoreactor—a highly accelerated first-principles molecular dynamics simulation of chemical reactions that discovers new molecules and mechanisms without preordained reaction coordinates or elementary steps. Using the nanoreactor, we show new pathways for glycine synthesis from primitive compounds proposed to exist on the early Earth, which provide new insight into the classic Urey-Miller experiment. These results highlight the emergence of theoretical and computational chemistry as a tool for discovery, in addition to its traditional role of interpreting experimental findings.
Operator evolution for ab initio nuclear theory
Schuster, Micah D; Johnson, Calvin W; Jurgenson, Eric D; Navratil, Petr
2014-01-01
The past two decades have seen a revolution in ab initio calculations of nuclear properties. One key element has been the development of a rigorous effective interaction theory, applying unitary transformations to soften the nuclear Hamiltonian and hence accelerate the convergence as a function of the model space size. For consistency, however, one ought to apply the same transformation to other operators when calculating transitions and mean values from the eigenstates of the renormalized Hamiltonian. Working in a translationally-invariant harmonic oscillator basis for the two- and three-nucleon systems, we evolve the Hamiltonian, square-radius and total dipole strength operators by the similarity renormalization group (SRG). The inclusion of up to three-body matrix elements in the 4He nucleus all but completely restores the invariance of the expectation values under the transformation. We also consider a Gaussian operator with adjustable range and find at short ranges an increased contribution from such ind...
Ab initio alpha-alpha scattering
Elhatisari, Serdar; Rupak, Gautam; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A; Luu, Thomas; Meißner, Ulf-G
2015-01-01
Processes involving alpha particles and alpha-like nuclei comprise a major part of stellar nucleosynthesis and hypothesized mechanisms for thermonuclear supernovae. In an effort towards understanding alpha processes from first principles, we describe in this letter the first ab initio calculation of alpha-alpha scattering. We use lattice effective field theory to describe the low-energy interactions of nucleons and apply a technique called the adiabatic projection method to reduce the eight-body system to an effective two-cluster system. We find good agreement between lattice results and experimental phase shifts for S-wave and D-wave scattering. The computational scaling with particle number suggests that alpha processes involving heavier nuclei are also within reach in the near future.
Energy Technology Data Exchange (ETDEWEB)
Bernard, S.; Jollet, F.; Jomard, G.; Siberchicot, B.; Torrent, M.; Zerah, G.; Amadon, B.; Bouchet, J.; Richard, N.; Robert, G. [CEA Bruyeres-le-Chatel, 91 (France)
2005-07-01
The determination of equations of states of heavy metals through ab initio calculation, i.e. without any adjustable parameter, allows to access to pressure and temperature thermodynamic conditions sometimes inaccessible to experiment. To perform such calculations, density functional theory (DFT) is a good starting point: when electronic densities are homogeneous enough, the local density approximation (LDA) remarkably accounts for thermodynamic properties of heavy metals, such as tantalum, or the light actinides, as well for static properties - equilibrium volume, elastic constants - as for dynamical quantities like phonon spectra. For heavier elements, like neptunium or plutonium, relativistic effects and strong electronic interactions must be taken into account, which requires more sophisticated theoretical approaches. (authors)
Haddadi, K.; Bouhemadou, A.; Bin-Omran, S.; Maabed, S.; Khenata, R.
2015-01-01
The structural parameters, elastic constants, electronic structure and optical properties of the recently reported monoclinic quaternary nitridoaluminate LiCaAlN2 are investigated in detail using the ab initio plane-wave pseudopotential method within the generalized gradient approximation. The calculated equilibrium structural parameters are in excellent agreement with the experimental data, which validate the reliability of the applied theoretical method. The chemical and structural stabilities of LiCaAlN2 are confirmed by calculating the cohesion energy and enthalpy of formation. Chemical band stiffness is calculated to explain the pressure dependence of the lattice parameters. Through the band structure calculation, LiCaAlN2 is predicted to be an indirect band gap of 2.725 eV. The charge-carrier effective masses are estimated from the band structure dispersions. The frequency-dependent dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity coefficient and electron energy loss function spectra are calculated for polarized incident light in a wide energy range. Optical spectra exhibit a noticeable anisotropy. Single-crystal and polycrystalline elastic constants and related properties, including isotropic sound velocities and Debye temperatures, are numerically estimated. The calculated elastic constants and elastic compliances are used to analyse and visualize the elastic anisotropy of LiCaAlN2. The calculated elastic constants demonstrate the mechanical stability and brittle behaviour of the considered material.
Chen, K X; Wu, J A; Ji, R Y
1987-09-01
We investigated the cis- and trans-isomers of Pt(NH3)2Cl2 and [Pt(NH3)2]2+ using a quantum chemical non-empirical calculation method, the pseudopotential valence electron-only ab initio method. The electronic structure and electrostatic potential counter maps were in turn determined through the wave functions so obtained. There was a sharp difference between the dipole moments of the cis- and trans-isomers. The electrostatic counter maps of the isomers also had remarkably different features. Based on the interaction between the platinum (II) coordination compound and the base pairs of nucleic acid, the difference in antitumour activity of the isomeric compounds was discussed. It is pointed out that the key factor for antitumour activity is that the platinum (II) coordination compound must be mutually complementary with the target acceptor in both configuration and bonding activity. This mutual-complementary requirement includes a bonding ability of the platinum complex with two negative centers in DNA, so as to form an intrastrand crosslink with two neighbouring guanines.
Institute of Scientific and Technical Information of China (English)
WANG Dajun; XIA Shangda; YIN Min
2008-01-01
The ab initio self-consistent DV-Xα (discrete variational Xα) method was used in its relativistic and spin-polarized model to investigate the ground-state electronic structures of the crystal YPO4 and YPO4:RE3+ (RE=Ce, Pr and Sm) and f-d transition energies of the lattice. The calculation was performed on the clusters Y5P10O32 and REY4P10O32 embedded in a microcrystal containing about 1500 ions, respectively. The ground-state calculation provided the locations of the 4f and 5d crystal-field one-electron levels of RE3+ relative to the valence and conduction bands of host, the curve of total and the partial density of states, and the corresponding occupation numbers, etc. Especially, the transition-state calculation was performed to obtain the 4f→5d transition energies of RE3+ in comparison to the experimental observations. The lattice relaxation caused by the dopant ion RE3+ was discussed based on the total energy calculation and the transition-state calculation of the f-d transition energies.
Morphing ab initio potential energy curve of beryllium monohydride
Špirko, Vladimír
2016-12-01
Effective (mass-dependent) potential energy curves of the ground electronic states of 9BeH, 9BeD, and 9BeT are constructed by morphing a very accurate MR-ACPF ab initio potential of Koput (2011) within the framework of the reduced potential energy curve approach of Jenč (1983). The morphing is performed by fitting the RPC parameters to available experimental ro-vibrational data. The resulting potential energy curves provide a fairly quantitative reproduction of the fitted data. This allows for a reliable prediction of the so-far unobserved molecular states in terms of only a small number of fitting parameters.
Hydrogen Desorption from Mg Hydride: An Ab Initio Study
Directory of Open Access Journals (Sweden)
Simone Giusepponi
2012-07-01
Full Text Available Hydrogen desorption from hydride matrix is still an open field of research. By means of accurate first-principle molecular dynamics (MD simulations an Mg–MgH2 interface is selected, studied and characterized. Electronic structure calculations are used to determine the equilibrium properties and the behavior of the surfaces in terms of structural deformations and total energy considerations. Furthermore, extensive ab-initio molecular dynamics simulations are performed at several temperatures to characterize the desorption process at the interface. The numerical model successfully reproduces the experimental desorption temperature for the hydride.
Saito, Minoru; Kashiwagi, Hiroshi
1985-04-01
For bis(pyridine)(porphinato) iron [FeP(py)2], a correlation between the iron electronic state and the equilibrium Fe-Npy distance was investigated. Potential energy curves as a function of the Fe-Npy distance were calculated for low-spin, intermediate-spin, and high-spin states of the ferric and ferrous ions by the ab initio SCF MO method. The equilibrium Fe-Npy distances were obtained from the potential curves. The values obtained for the ferric low-spin and high-spin states were in good agreement with the experimental values for Fe(III)(OEP)(3-Clpy)2 within the differences, ±0.05 Å. The following significant features were found. The equilibrium distance is elongated by the occupation of the 3dz2 orbital and is shortened by the oxidation of the iron atom. The distance and the force constant for the symmetrical py-Fe-py stretching are strongly correlated with the overlap population between the 3dz2 orbital and pyridine-nitrogen orbitals.
Energy Technology Data Exchange (ETDEWEB)
Ciftci, Yasemin Oe. [Gazi Univ., Ankara (Turkey). Dept. of Physics; Coban, Cansu [Balikesir Univ. (Turkey). Dept. of Physics
2016-05-01
The structural, mechanical, electronic, dynamic, and optical properties of the ZrPdSn compound crystallising into the MgAgAs structure are investigated by the ab initio calculations based on the density functional theory. The lattice constant, bulk modulus, and first derivative of bulk modulus were obtained by fitting the calculated total energy-atomic volume results to the Murnaghan equation of state. These results were compared to the previous data. The band structure and corresponding density of states (DOS) were also calculated and discussed. The elastic properties were calculated by using the stress-strain method, which shows that the MgAgAs phase of this compound is mechanically stable. The presented phonon dispersion curves and one-phonon DOS confirms that this compound is dynamically stable. In addition, the heat capacity, entropy, and free energy of ZrPdSn were calculated by using the phonon frequencies. Finally, the optical properties, such as dielectric function, reflectivity function, extinction coefficient, refractive index, and energy loss spectrum, were obtained under different pressures.
Parisi, Filippo; Sciascia, Luciana; Princivalle, Francesco; Merli, Marcello
2012-02-01
In order to characterize the pressure-induced decomposition of ringwoodite (γ-Mg2SiO4), the topological analysis of the electron density ρ( r), based upon the theory of atoms in molecules (AIM) developed by Bader in the framework of the catastrophe theory, has been performed. Calculations have been carried out by means of the ab initio CRYSTAL09 code at the HF/DFT level, using Hamiltonians based on the Becke- LYP scheme containing hybrid Hartree-Fock/density functional exchange-correlation terms. The equation of state at 0 K has been constructed for the three phases involved in the post-spinel phase transition (ringwoodite → Mg-perovskite + periclase) occurring at the transition zone-lower mantel boundary. The topological results show that the decomposition of the ringwoodite at high pressures is caused by a conflict catastrophe. Furthermore, topological evidences of the central role played by the oxygen atoms to facilitate the pressure-induced ringwoodite decomposition and the subsequent phase transition have been noticed.
Demkov, Alexander A.; Navrotsky, Alexandra
2001-03-01
The International Technology Roadmap for Semiconductors (ITRS) predicts that the strategy of scaling complementary metal-oxide-semiconductor (CMOS) devices will come to an abrupt end around the year 2012. The main reason for this will be the unacceptably high leakage current through the silicon dioxide gate with a thickness below 20 ÅFinding a gate insulator alternative to SiO2 has proven to be far from trivial. Hafnium and zirconium dioxides and silicates have been recently considered as gate dielectrics with intermediate dielectric constants. Hafnia and ziconia are important ceramic materials as well, and their phase relations are rather well studied. There is also interest in hafnia as a constituent of ceramic waste forms for plutonium, based on its refractory nature and high neutron absorption cross section. We use a combination of the ab-initio calculations and calorimetry to investigate thermodynamic and electronic properties of hafnia and zirconia. We describe the cubic to tetragonal phase transition in the fluorite structure by computing the total energy surface for zone-edge distortions correct to fourth order in the soft-mode displacement with the strain coupling renormalization included. We compare the two materials using some simple chemical concepts.
Tuna, Deniz; Udvarhelyi, Anikó; Sobolewski, Andrzej L; Domcke, Wolfgang; Domratcheva, Tatiana
2016-04-14
Eumelanin is a naturally occurring skin pigment which is responsible for developing a suntan. The complex structure of eumelanin consists of π-stacked oligomers of various indole derivatives, such as the monomeric building block 5,6-dihydroxyindole (DHI). In this work, we present an ab initio wave-function study of the absorption behavior of DHI oligomers and of doubly and triply π-stacked species of these oligomers. We have simulated the onset of the electronic absorption spectra by employing the MP2 and the linear-response CC2 methods. Our results demonstrate the effect of an increasing degree of oligomerization of DHI and of an increasing degree of π-stacking of DHI oligomers on the onset of the absorption spectra and on the degree of red-shift toward the visible region of the spectrum. We find that π-stacking of DHI and its oligomers substantially red-shifts the onset of the absorption spectra. Our results also suggest that the optical properties of biological eumelanin cannot be simulated by considering the DHI building blocks alone, but instead the building blocks indole-semiquinone and indole-quinone have to be considered as well. This study contributes to advancing the understanding of the complex photophysics of the eumelanin biopolymer.
Energy Technology Data Exchange (ETDEWEB)
Raybaud, P.; Hafner, J.; Kresse, G.; Kasztelan, S.; Toulhoat, H.
2000-02-15
The determination of the local structure of cobalt- or nickel-promoted MoS{sub 2}-based hydrodesulfurization catalysts is of interest for understanding the mechanism leading to an increased activity brought by cobalt or nickel, the so-called synergetic effect. For that reason, the authors carried out ab initio calculations using density functional theory under the generalized gradient approximation for periodic systems. The edge substitution model emerges as the most stable structure and provides an excellent agreement with local structures experimentally determined on real catalysts by in situ extended X-ray absorption fine structure. The authors studied the absorption of sulfur on the active edge surface of the promoted MoS{sub 2} catalyst and determined the equilibrium coverage under sulfiding conditions. It is demonstrated that the incorporation of promoter atoms has a strong influence on the sulfur-metal bond energy at the surface and in particular leads to a reduction of the equilibrium S coverage of the active metal sites. A comparative study on the effects of Co, Ni, and Cu atoms as promoters was performed. Detailed results on the surface electronic structure of promoted MoS{sub 2} are presented.
On the hierarchical parallelization of ab initio simulations
Ruiz-Barragan, Sergi; Shiga, Motoyuki
2016-01-01
A hierarchical parallelization has been implemented in a new unified code PIMD-SMASH for ab initio simulation where the replicas and the Born-Oppenheimer forces are parallelized. It is demonstrated that ab initio path integral molecular dynamics simulations can be carried out very efficiently for systems up to a few tens of water molecules. The code was then used to study a Diels-Alder reaction of cyclopentadiene and butenone by ab initio string method. A reduction in the reaction energy barrier is found in the presence of hydrogen-bonded water, in accordance with experiment.
Energy Technology Data Exchange (ETDEWEB)
Reffas, M. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria); Bouhemadou, A., E-mail: a_bouhemadou@yahoo.f [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria); Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Khenata, R. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Laboratoire de Physique Theorique, B.P. 230, Universite de Tlemcen, Tlemcen 13000 (Algeria); Ouahrani, T. [Laboratoire de Physique Quantique et de Modelisation Mathematique, Universite de Mascara, 29000 Mascara (Algeria); Bin-Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia)
2010-09-15
Ab initio study of structural, elastic, electronic and optical properties of the cubic spinel oxide SnMg{sub 2}O{sub 4} has been reported using the pseudo-potential plane-wave method within the local density approximation and the gradient generalized approximation for the exchange and correlation potential. Computed lattice constant and internal free parameters are in good agreement with the available experimental results. The elastic constants and their pressure dependence are predicted using the static finite strain technique. A linear pressure dependence of the elastic stiffnesses is found. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young's modulus, Poisson's ratio, Lame's coefficients, average sound velocity and Debye temperature are numerically estimated in the frame-work of the Voigt-Reuss-Hill approximation for SnMg{sub 2}O{sub 4} polycrystalline. Band structure shows that SnMg{sub 2}O{sub 4} has a direct band gap ({Gamma}-{Gamma}), which increases with increase in pressure. Density of states and Mulliken population analysis show that the Mg-O bond is typically covalent due to the O-2p and Mg-2p states hybridizations. In order to understand the optical properties of SnMg{sub 2}O{sub 4}, the dielectric function, optical reflectivity, refractive index, extinction coefficient and electron energy loss function are calculated for radiation up to 40 eV. The pressure dependence of the zero-frequency limit of the real part of the dielectric function {epsilon}{sub 1}(0) and of the refractive index n(0) has been investigated. This is the first quantitative theoretical prediction of the elastic, electronic and optical properties of the SnMg{sub 2}O{sub 4} compound, and it still awaits experimental confirmation.
Ab initio calculation of the Hoyle state
Epelbaum, Evgeny; Lee, Dean; Meißner, Ulf-G
2011-01-01
The Hoyle state plays a crucial role in the hydrogen burning of stars heavier than our sun and in the production of carbon and other elements necessary for life. This excited state of the carbon-12 nucleus was postulated by Hoyle^{1} as a necessary ingredient for the fusion of three alpha particles to produce carbon at stellar temperatures. Although the Hoyle state was seen experimentally more than a half century ago^{2,3}, nuclear theorists have not yet uncovered the nature of this state from first principles. In this letter we report the first ab initio calculation of the low-lying states of carbon-12 using supercomputer lattice simulations and a theoretical framework known as effective field theory. In addition to the ground state and excited spin-2 state, we find a resonance at -85(3) MeV with all of properties of the Hoyle state and in agreement with the experimentally observed energy. These lattice simulations provide insight into the structure of this unique state and new clues as to the amount of fine...
Ab initio phase diagram of iridium
Burakovsky, L.; Burakovsky, N.; Cawkwell, M. J.; Preston, D. L.; Errandonea, D.; Simak, S. I.
2016-09-01
The phase diagram of iridium is investigated using the Z methodology. The Z methodology is a technique for phase diagram studies that combines the direct Z method for the computation of melting curves and the inverse Z method for the calculation of solid-solid phase boundaries. In the direct Z method, the solid phases along the melting curve are determined by comparing the solid-liquid equilibrium boundaries of candidate crystal structures. The inverse Z method involves quenching the liquid into the most stable solid phase at various temperatures and pressures to locate a solid-solid boundary. Although excellent agreement with the available experimental data (to ≲65 GPa) is found for the equation of state (EOS) of Ir, it is the third-order Birch-Murnaghan EOS with B0'=5 rather than the more widely accepted B0'=4 that describes our ab initio data to higher pressure (P ) . Our results suggest the existence of a random-stacking hexagonal close-packed structure of iridium at high P . We offer an explanation for the 14-layer hexagonal structure observed in experiments by Cerenius and Dubrovinsky.
Ab initio materials physics and microscopic electrodynamics of media
2016-01-01
We argue that the amazing progress of first-principles materials physics necessitates a revision of the Standard Approach to electrodynamics of media. We hence subject this Standard Approach to a thorough critique, which shows both its inherent conceptual problems and its practical inapplicability to modern ab initio calculations. We then go on to show that the common practice in ab initio materials physics has overcome these difficulties by taking a different, microscopic approach to electro...
Interatomic Coulombic decay widths of helium trimer: Ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Kolorenč, Přemysl, E-mail: kolorenc@mbox.troja.mff.cuni.cz [Charles University in Prague, Faculty of Mathematics and Physics, Institute of Theoretical Physics, V Holešovičkách 2, 180 00 Prague (Czech Republic); Sisourat, Nicolas [Sorbonne Universités, UPMC Univ Paris 06, UMR 7614, Laboratoire de Chimie Physique Matière et Rayonnement, F-75005 Paris (France); CNRS, UMR 7614, Laboratoire de Chimie Physique Matière et Rayonnement, F-75005 Paris (France)
2015-12-14
We report on an extensive study of interatomic Coulombic decay (ICD) widths in helium trimer computed using a fully ab initio method based on the Fano theory of resonances. Algebraic diagrammatic construction for one-particle Green’s function is utilized for the solution of the many-electron problem. An advanced and universal approach to partitioning of the configuration space into discrete states and continuum subspaces is described and employed. Total decay widths are presented for all ICD-active states of the trimer characterized by one-site ionization and additional excitation of an electron into the second shell. Selected partial decay widths are analyzed in detail, showing how three-body effects can qualitatively change the character of certain relaxation transitions. Previously unreported type of three-electron decay processes is identified in one class of the metastable states.
Energy Technology Data Exchange (ETDEWEB)
Neef, Matthias
2007-03-19
Aim of this thesis was to reach by a systematic study of different ab initio procedures an improved description of the electronic properties of FeSi and FeGe. Central result is the itinerant description of FeSi as a semiconductor in the neighbourhood of a ferromagnetic instability. The regardment of the nonlocal exchange in the effective one-particle approximation leads to a metastable magnetic state scarcely above the magnetic ground state. The application of the hybrid functional leads to a 1st order metal-isolator transition for large lattice parameters: FeSi transforms at increasement of the lattice parameter from an unmagnetic isolator to a magnetic metal. A similar behavior is found in the isostructural compound FeGe. The two systems FeSi and FeGe were systematically and detailedly analyzed by means of ab initio procedures. Thereby the structural, electronic, and magnetic properties were studied with DFT and HF calculations. Both calculations with spin polarization and without spin polarization were performed.
Marsalek, Ondrej; Markland, Thomas E
2017-03-22
Understanding the reactivity and spectroscopy of aqueous solutions at the atomistic level is crucial for the elucidation and design of chemical processes. However, the simulation of these systems requires addressing the formidable challenges of treating the quantum nature of both the electrons and nuclei. Exploiting our recently developed methods that provide acceleration by up to 2 orders of magnitude, we combine path integral simulations with on-the-fly evaluation of the electronic structure at the hybrid density functional theory level to capture the interplay between nuclear quantum effects and the electronic surface. Here we show that this combination provides accurate structure and dynamics, including the full infrared and Raman spectra of liquid water. This allows us to demonstrate and explain the failings of lower-level density functionals for dynamics and vibrational spectroscopy when the nuclei are treated quantum mechanically. These insights thus provide a foundation for the reliable investigation of spectroscopy and reactivity in aqueous environments.
Ab Initio Study of Electronic Structure, Elastic and Transport Properties of Fluoroperovskite LiBeF3
Benmhidi, H.; Rached, H.; Rached, D.; Benkabou, M.
2017-04-01
The aim of this work is to investigate the electronic, mechanical, and transport properties of the fluoroperovskite compound LiBeF3 by first-principles calculations using the full-potential linear muffin-tin orbital method based on density functional theory within the local density approximation. The independent elastic constants and related mechanical properties including the bulk modulus ( B), shear modulus ( G), Young's modulus ( E), and Poisson's ratio ( ν) have been studied, yielding the elastic moduli, shear wave velocities, and Debye temperature. According to the electronic properties, this compound is an indirect-bandgap material, in good agreement with available theoretical data. The electron effective mass, hole effective mass, and energy bandgaps with their volume and pressure dependence are investigated for the first time.
Aleinikova, M. V.; Zhuravlev, Yu. N.; Korabelnikov, D. V.
2012-10-01
Within the framework of a gradient approximation of the all-electron density functional theory (DFT), using a linear combination of atomic orbitals of the CRYSTAL09 software package, the structural and electronic properties of lithium, sodium, and potassium oxides and peroxides are investigated under hydrostatic conditions in the range of pressures from -3 to 15 GPa. The crystal structure parameters are determined, the band structure, densities of state (DOSs), atomic charges, and overlap populations are calculated, and their dependence on pressure is established. The energy band gap is shown to increase with pressure.
Institute of Scientific and Technical Information of China (English)
H. Koc; A. Yildirim; E. Deligoz
2012-01-01
The structural,elastic,electronic,optical,and vibrational properties of cubic PdGa compound are investigated using the norm-conserving pseudopotentials within the local density approximation (LDA) in the framework of the density functional theory.The calculated lattice constant has been compared with the experimental value and has been found to be in good agreement with experimental data.The obtained electronic band structures show that PdGa compound has no band gap.The second-order elastic constants have been calculated,and the other related quantities such as the Young's modulus,shear modulus,Poisson's ratio,anisotropy factor,sound velocities,and Debye temperature have also been estimated.Our calculated results of elastic constants show that this compound is mechanically stable.Furthermore,the real and imaginary parts of the dielectric function and the optical constants such as the electron energy-loss function,the optical dielectric constant and the effective number of electrons per unit cell are calculated and presented in the study.The phonon dispersion curves are also derived using the direct method.
Energy Technology Data Exchange (ETDEWEB)
Boyé-Péronne, Séverine; Gauyacq, Dolores [Institut des Sciences Moléculaires d’Orsay, UMR 8214, CNRS and Université Paris-Sud, Bât. 210, F-91405 Orsay Cedex (France); Liévin, Jacques, E-mail: jlievin@ulb.ac.be [Service de Chimie Quantique et Photophysique, Université Libre de Bruxelles, Cpi 160/09, 50 Av. F.D. Roosevelt, B-1050 Bruxelles (Belgium)
2014-11-07
The first quantitative description of the Rydberg and valence singlet electronic states of vinylidene lying in the 0–10 eV region is performed by using large scale ab initio calculations. A deep analysis of Rydberg-valence interactions has been achieved thanks to the comprehensive information contained in the accurate Multi-Reference Configuration Interaction wavefunctions and an original population analysis highlighting the respective role played by orbital and state mixing in such interactions. The present theoretical approach is thus adequate for dealing with larger than diatomic Rydberg systems. The nine lowest singlet valence states have been optimized. Among them, some are involved in strong Rydberg-valence interactions in the region of the Rydberg state equilibrium geometry. The Rydberg states of vinylidene present a great similarity with the acetylene isomer, concerning their quantum defects and Rydberg molecular orbital character. As in acetylene, strong s-d mixing is revealed in the n = 3 s-d supercomplex. Nevertheless, unlike in acetylene, the close-energy of the two vinylidene ionic cores {sup 2}A{sub 1} and {sup 2}B{sub 1} results into two overlapped Rydberg series. These Rydberg series exhibit local perturbations when an accidental degeneracy occurs between them and results in avoided crossings. In addition, some Δl = 1 (s-p and p-d) mixings arise for some Rydberg states and are rationalized in term of electrostatic interaction from the electric dipole moment of the ionic core. The strongest dipole moment of the {sup 2}B{sub 1} cationic state also stabilizes the lowest members of the n = 3 Rydberg series converging to this excited state, as compared to the adjacent series converging toward the {sup 2}A{sub 1} ionic ground state. The overall energies of vinylidene Rydberg states lie above their acetylene counterpart. Finally, predictions for optical transitions in singlet vinylidene are suggested for further experimental spectroscopic
Ab initio study of the structural and electronic properties of the complex structures of RuO 2
Benyahia, K.; Nabi, Z.; Tadjer, A.; Khalfi, A.
2003-11-01
We have studied structural and electronic properties of RuO 2 in the two complex structures (rutile and orthorhombic) by means of accurate first principle total energy calculations using the full potential linearized augmented plane wave (FP-LAPW). The calculations are presented within the local-density approximation and the generalized gradient approximation. The orthorhombic (CaCl 2-type Pnnm) structure is just a deformation of the rutile (P4 2/mnm). Until now, considerable work has been performed on the rutile structure; however, no work has been performed on the orthorhombic structure. The structural properties are in good agreement with experiment. Our calculations of the electronic properties have been compared with experiment and previous calculations and a good agreement is found.
Ab initio study of the structural and electronic properties of the complex structures of RuO{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Benyahia, K.; Nabi, Z.; Tadjer, A.; Khalfi, A
2003-11-01
We have studied structural and electronic properties of RuO{sub 2} in the two complex structures (rutile and orthorhombic) by means of accurate first principle total energy calculations using the full potential linearized augmented plane wave (FP-LAPW). The calculations are presented within the local-density approximation and the generalized gradient approximation. The orthorhombic (CaCl{sub 2}-type Pnnm) structure is just a deformation of the rutile (P4{sub 2}/mnm). Until now, considerable work has been performed on the rutile structure; however, no work has been performed on the orthorhombic structure. The structural properties are in good agreement with experiment. Our calculations of the electronic properties have been compared with experiment and previous calculations and a good agreement is found.
Liu, Jin; Prezhdo, Oleg V
2015-11-19
Rapid development in lead halide perovskites has led to solution-processable thin film solar cells with power conversion efficiencies close to 20%. Nonradiative electron-hole recombination within perovskites has been identified as the main pathway of energy losses, competing with charge transport and limiting the efficiency. Using nonadiabatic (NA) molecular dynamics, combined with time-domain density functional theory, we show that nonradiative recombination happens faster than radiative recombination and long-range charge transfer to an acceptor material. Doping of lead iodide perovskites with chlorine atoms reduces charge recombination. On the one hand, chlorines decrease the NA coupling because they contribute little to the wave functions of the valence and conduction band edges. On the other hand, chlorines shorten coherence time because they are lighter than iodines and introduce high-frequency modes. Both factors favor longer excited-state lifetimes. The simulation shows good agreement with the available experimental data and contributes to the comprehensive understanding of electronic and vibrational dynamics in perovskites. The generated insights into design of higher-efficiency solar cells range from fundamental scientific principles, such as the role of electron-vibrational coupling and quantum coherence, to practical guidelines, such as specific suggestions for chemical doping.
Benlamari, S.; Amara Korba, S.; Lakel, S.; Meradji, H.; Ghemid, S.; El Haj Hassan, F.
2016-01-01
The structural, elastic, thermal and electronic properties of perovskite hydrides SrLiH3 and SrPdH3 have been investigated using the all-electron full-potential linear augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). For the exchange-correlation potential, local-density approximation (LDA) and generalized gradient approximation (GGA) have been used to calculate theoretical lattice parameters, bulk modulus, and its pressure derivative. The present results are in good agreement with available theoretical and experimental data. The three independent elastic constants (C11, C12 and C44) are also reported. From electronic band structure and density of states (DOSs), it is found that SrLiH3 is an insulator characterized by an indirect gap of 3.48 eV, while SrPdH3 is metallic with a calculated DOSs at Fermi energy of 0.745 states/eV-unit cell. Poisson’s ratio (σ), Young’s modulus (E), shear modulus (G), anisotropy factor (A), average sound velocities (vm) and density (ρ) of these compounds are also estimated for the first time. The Debye temperature is deduced from the average sound velocity. Variation of elastic constants and bulk modulus of these compounds as a function of pressure is also reported. Pressure and thermal effects on some macroscopic properties are predicted using the quasi-harmonic Debye model.
DEFF Research Database (Denmark)
Chaban, Vitaly V.; Prezhdo, Victor; Prezhdo, Oleg
2013-01-01
Nonadiabatic molecular dynamics combined with time-domain density functional theory are used to study electron transfer (ET) from a CdSe quantum dot (QD) to the C-60 fullerene, occurring in several types of hybrid organic/inorganic nanocomposites. By unveiling the time dependence of the ET process......, it leads to a notably weaker QD-C-60 interaction than a lengthy molecular bridge. We show that the ET rate in a nonbonded mixture of QDs and C-60 can be enhanced by doping. The photoinduced ET is promoted primarily by mid- and low-frequency vibrations. The study establishes the basic design principles...
Kenfack, Cyril A; Klymchenko, Andrey S; Duportail, Guy; Burger, Alain; Mély, Yves
2012-07-07
The electronic transitions occurring in 4-(N,N-dimethylamino)-3-hydroxyflavone (DMAF) and 2-furanyl-3-hydroxychromone (FHC) were investigated using the TDDFT method in aprotic and protic solvents. The solvent effect was incorporated into the calculations via the PCM formalism. The H-bonding between solute and protic solvent was taken into account by considering a molecular complex between these molecules. To examine the effect of the H-bond on the ESIPT reaction, the absorption and emission wavelengths as well as the energies of the different states that intervene during these electronic transitions were calculated in acetonitrile, ethanol and methanol. The calculated positions of the absorption and emission wavelengths in various solvents were in excellent agreement with the experimental spectra, validating our approach. We found that in DMAF, the hydrogen bonding with protic solvents makes the ESIPT reaction energetically unfavourable, which explains the absence of the ESIPT tautomer emission in protic solvents. In contrast, the excited tautomer state of FHC remains energetically favourable in both aprotic and protic solvents. Comparing our calculations with the previously reported time-resolved fluorescence data, the ESIPT reaction of DMAF in aprotic solvents is reversible because the emitting states are energetically close, whereas in FHC, ESIPT is irreversible because the tautomer state is below the corresponding normal state. Therefore, the ESIPT reaction in DMAF is controlled by the relative energies of the excited states (thermodynamic control), while in FHC the ESIPT is controlled probably by the energetic barrier (kinetic control).
Strong electron-phonon coupling in Be{1-x}B{2}C{2}: ab initio studies
Moudden, A. H.
2008-07-01
Several structures for off-stoichiometric beryllium diboride dicarbide Be{1-x}B2C2 have been designed, and their properties studied from first-principles density functional methods. Among the most stable phases examined, the layered hexagonal structures are shown to exhibit various features in the electronic properties and in the lattice dynamics reminiscent of the superconducting magnesium diboride and alkaline earth-intercalated graphites. For substoichiometric composition x˜ 1/3, the system is found metallic with a moderately strong electron-phonon coupling through a predominant contribution arising from high frequency streching modes modulating the σ-bonding of the B C network, and a weaker contribution at medium frequency range of the phonon spectra, arising from the intercalent motion coupled to the π-bonding states. Further, anharmonicities emerging from the proximity of the Fermi level to the σ-band edge, contributes to reduce the phonon softening hence stabilizing the structure. All these effects appear to combine favourably to produce a high temperature phonon-superconductivity.
Ab initio study of electron energy loss spectra of bulk bismuth up to 100 eV
Timrov, Iurii; Markov, Maxime; Gorni, Tommaso; Raynaud, Michèle; Motornyi, Oleksandr; Gebauer, Ralph; Baroni, Stefano; Vast, Nathalie
2017-03-01
The dynamical charge-density response of bulk bismuth has been studied within time-dependent density functional perturbation theory, explicitly accounting for spin-orbit coupling. The use of the Liouville-Lanczos approach allows us to calculate electron energy loss spectra for excitation energies as large as 100 eV. Effects of 5 d semicore electronic states, spin-orbit coupling, exchange and correlation, local fields, and anisotropy are thoroughly investigated. The account of the 5 d states in the calculation turns out to be crucial to correctly describe the loss spectra above 10 eV and, in particular, the position and shape of the bulk-plasmon peak at 14.0 eV at vanishing transferred momentum. Our calculations reveal the presence of interband transitions at 16.3 eV, which had never been discussed before. The origin of the peak at 5.8 eV is revisited as due to mixed interband and collective excitations. Finally, our study supplements the lack of experiments at finite transferred momenta.
Nenov, Artur; Rivalta, Ivan; Cerullo, Giulio; Mukamel, Shaul; Garavelli, Marco
2014-02-20
Two-dimensional (2D) optical spectroscopy techniques based on ultrashort laser pulses have been recently extended to the optical domain in the ultraviolet (UV) spectral region. UV-active aromatic side chains can thus be used as local highly specific markers for tracking dynamics and structural rearrangements of proteins. Here we demonstrate that 2D electronic spectra of a model proteic system, a tetrapeptide with two aromatic side chains, contain enough structural information to distinguish between two different configurations with distant and vicinal side chains. For accurate simulations of the 2DUV spectra in solution, we combine a quantum mechanics/molecular mechanics approach based on wave function methods, accounting for interchromophores coupling and environmental effects, with nonlinear response theory. The proposed methodology reveals effects, such as charge transfer between vicinal aromatic residues that remain concealed in conventional exciton Hamiltonian approaches. Possible experimental setups are discussed, including multicolor experiments and signal manipulation techniques for limiting undesired background contributions and enhancing 2DUV signatures of specific electronic couplings.
Directory of Open Access Journals (Sweden)
V.O. Kharchenko
2015-06-01
Full Text Available Within this paper we have the studied structural and electronic properties of zirconium crystal with vacancies from the first principles. We have defined the optimal values for the lattice constants. The corresponding densities of states and energetic spectrum were calculated. These results gave a possibility to define the Fermi structure of the zirconium crystal with vacancies. In the framework of the molecular dynamics simulations we have studied the dynamics of the ensemble of periodically located vacancies in the zirconium crystal with an increase in temperature. We have analyzed the reconstruction of atomic structure and change in the total volume of the crystal with the temperature growth. The dependencies of the volume expansion coefficient for the pure zirconium without vacancies end zirconium crystal with different vacancies concentration on the temperature were studied.
Bensadiq, A.; Zaari, H.; Benyoussef, A.; El Kenz, A.
2016-09-01
Using the density functional theory, the electronic structure; density of states, band structure and exchange couplings of Tb Ni4 Si compound have been investigated. Magnetic and magnetocaloric properties of this material have been studied using Monte Carlo Simulation (MCS) and Mean Field Approximation (MFA) within a three dimensional Ising model. We calculated the isothermal magnetic entropy change, adiabatic temperature change and relative cooling power (RCP) for different external magnetic field and temperature. The highest obtained isothermal magnetic entropy change is of -14.52 J kg-1 K-1 for a magnetic field of H=4 T. The adiabatic temperature reaches a maximum value equal to 3.7 K and the RCP maximum value is found to be 125.12 J kg-1 for a field magnetic of 14 T.
Erkişi, Aytaç; Yıldırım, Erdem Kamil; Gökoğlu, Gökhan
2014-08-01
We present the electronic, magnetic and structural properties of the magnetic transition metal oxides PbMO3 (M = Fe, Co, Ni) in cubic perovskite structure. The calculations are based on the density functional theory (DFT) within plane-wave pseudopotential method and local spin density approximation (LSDA) of the exchange-correlation functional. On-site Coulomb interaction is also included in calculations (LSDA+U). The systems are considered in ferromagnetic (FM) and G-type antiferromagnetic (G-AFM) order. FM structures are energetically more favored than G-AFM and than non-magnetic states for all the systems studied. The spin-polarized electronic band structures show that all the structures have metallic property in FM order without Hubbard-U interaction (Ueff = 0). However, the inclusion of on-site Coulomb interaction (Ueff = 7 eV) opens a semiconducting gap for majority spin channel of PbFeO3 and of PbNiO3 resulting in a half-metallic character. PbCoO3 system remains as metallic with LSDA+U scheme. Bonding features of all structures are largely determined by the hybridizations between O-p and d-states of transition metal atoms. The partial magnetic moment of Fe atom in PbFeO3 is enhanced by inclusion of Hubbard-U interaction (2.55 μB ⇒ 3.78 μB). Total magnetic moments of half-metallic PbFeO3 and of PbNiO3 compounds are very close to integer values.
Ab initio study of structural and electronic properties of (GaN)n/(AlN)n superlattices
Djoudi, L.; Merabet, M.; Dahmane, F.; Boucharef, M.; Benalia, S.; Rached, D.
2016-10-01
Structural and electronic properties of binary GaN and AlN compounds and their superlattices (SLs) (GaN)n/(AlN)n are investigated using the first-principles full potential linear muffin-tin orbitals method (FP-LMTO). The exchange-correlation potential is treated with the local density approximation of Perdew and Wang (LDA-PW). The ground-state properties are determined for the bulk materials GaN, AlN, and their superlattices (GaN)n/(AlN)n) in cubic phase. The calculated structural properties of GaN and AlN compounds are in good agreement with available experimental and theoretical data. It is found that AlN exhibit an indirect fundamental band gap while that GaN and the superlattices (SLs) exhibit a direct fundamental band gap, which might make the superlattices (GaN)n/(AlN)n materials promising and useful for optoelectronic applications. The fundamental band gap decreases with increasing the number of monolayer.
Institute of Scientific and Technical Information of China (English)
鄢国森; 先晖; 谢代前
1997-01-01
A 285-pomt multi-reference configuration-interaction involving single and double excitations ( MRS DCI) potential energy surface for the electronic ground state of L12H is determined by using 6-311G (2df,2pd)basis set.A Simons-Parr-Finlan polynomial expansion is used to fit the discrete surface with a x2 of 4.64×106 The equn librium geometry occurs at Rc=0.172 nm and,LiHL1=94.10°.The dissociation energy for reaction I2H(2A)→L12(1∑g)+H(2S) is 243.910 kJ/mol,and that for reaction L12H(2A’)→HL1(1∑) + L1(2S) is 106.445 kl/mol The inversion barrier height is 50.388 kj/mol.The vibrational energy levels are calculated using the discrete variable representation (DVR) method.
Energy Technology Data Exchange (ETDEWEB)
Bentouaf, Ali, E-mail: lilo.btf@gmail.com [Département de Physique, Faculté des Sciences, Université de Hassiba Ben Bouali, Chlef 02000 (Algeria); Hassan, Fouad El Haj [Université Libanaise, Faculté des Sciences (I), Laboratoire de Physique et d' Electronique (LPE), Elhadath, Beirut (Lebanon); Condensed Matter Section, The Abdus Salam International Centre for Theoretical Physics (ICTP), Strada Costiera 11, 34014 Trieste (Italy)
2015-05-01
Density functional theory based on full-potential linearized augmented plane wave (FP LAPW) method is used to investigate the structural, electronic and magnetic properties of Co{sub 2}VSi Heusler alloys, with L2{sub 1} structure. It is shown that calculated lattice constants and spin magnetic moments using the general gradient approximation method are in good agreement with experimental values. We also presented the thermal effects using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. Temperature and pressure effects on the structural parameters, heat capacities, thermal expansion coefficient, and Debye temperatures are determined from the non-equilibrium Gibbs functions. - Highlights: • Our calculated total magnetic moment is 2.96 μB. • The quasi-harmonic Debye model has been used to predict the thermal properties. • The GGA method is a good tool to calculate the magnetic moment. • The total DOS is calculated for the majority and minority spin densities. • The d–d hybridization is essential for the formation of the gap at E{sub F}.
Directory of Open Access Journals (Sweden)
H A Badehian
2015-07-01
Full Text Available In recent work the structural, electronic and optical properties of BSb compound in bulk and surface (110 states have been studied. Calculations have been performed using Full-Potential Augmented Plane Wave (FP-LAPW method by WIEN2k code in Density Functional Theory (DFT framework. The structural properties of the bulk such as lattice constant, bulk module and elastic constants have been investigated using four different approximations. The band gap energy of the bulk and the (110 surface of BSb were obtained about 1.082 and 0.38 eV respectively. Moreover the surface energy, the work function, the surface relaxation, surface state and the band structure of BSb (110 were investigated using symmetric and stoichiometric 15 layers slabs with the vacuum of 20 Bohr. In addition, the real and imaginary parts of the dielectric function of the bulk and the BSb (110 slab were calculated and compared to each other. Our obtained results have a good agreement with the available results.
Ab initio electronic transport study of two-dimensional silicon carbide-based p–n junctions
Zhou, Hanming; Lin, Xiao; Guo, Hongwei; Lin, Shisheng; Sun, Yiwei; Xu, Yang
2017-03-01
Two-dimensional silicon carbide (2d-SiC) is a viable material for next generation electronics due to its moderate, direct bandgap with huge potential. In particular, its potential for p–n junctions is yet to be explored. In this paper, three types of 2d-SiC-based p–n junctions with different doping configuration are modeled. The doping configurations refer to partially replacing carbon with boron or nitrogen atoms along the zigzag or armchair direction, respectively. By employing density functional theory, we calculate the transport properties of the SiC based p–n junctions and obtain negative differential resistance and high rectification ratio. We also find that the junction along the zigzag direction with lower doping density exhibits optimized rectification performance. Our study suggests that 2d-SiC is a promising candidate as a material platform for future nano-devices. Project supported by the National Science Foundation of China (Nos. 61474099, 61674127) and the ZJ-NSF (No. Z17F04003).
Energy Technology Data Exchange (ETDEWEB)
Chi, C.-C.; Hsiao, C.-H.; Ouyang, Chuenhou, E-mail: houyang@mx.nthu.edu.tw [Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan (China); Skoropata, E.; Lierop, J. van [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada)
2015-05-07
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 Co{sup 2+} 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.
Energy Technology Data Exchange (ETDEWEB)
Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Laboratory, Department of Physics, Islamia College Peshawar (Pakistan); Gupta, S.K. [Department of Physics, Michigan Technological University, Houghton, MI 49931 (United States); Seddik, T. [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 Mascara (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 Mascara (Algeria); Alahmed, Z.A. [Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451 (Saudi Arabia); Ahmed, R. [Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, UTM Skudai, 81310 Johor (Malaysia); Khachai, H. [Physics Department, Djillali Liabes University of Sidi Bel-Abbes (Algeria); Jha, P.K. [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar 364001 (India); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451 (Saudi Arabia)
2014-06-01
Highlights: • REGa{sub 3} (RE = Sc or Lu) compounds are mechanical stabile. • Both ScGa{sub 3} and LuGa{sub 3} exhibit metallic behavior just like other REGa{sub 3} compounds. • Melting temperature T{sub m} (K) for ScGa{sub 3} and LuGa{sub 3} are 1244.2 and 1143.8. • High absorption observed in the visible energy region. • The present study would be helpful for future experimental/theoretical explorations. - Abstract: Structural, elastic, optoelectronic and thermodynamic properties of REGa{sub 3} (RE = Sc and Lu) compounds have been studied self consistently by employing state of the art full potential (FP) linearized (L) approach of augmented plane wave (APW) plus local orbitals method. Calculations were executed at the level of Perdew–Burke and Ernzerhof (PBE) parameterized generalized gradient approximation (GGA) for exchange correlation functional in addition to modified Becke–Johnson (mBJ) potential. Our obtained results of lattice parameters show reasonable agreement to the previously reported experimental and other theoretical studies. Analysis of the calculated band structure of ScGa{sub 3} and LuGa{sub 3} compounds demonstrates their metallic character. Moreover, a positive value of calculated Cauchy pressure, in addition to reflecting their ductile nature, endorses their metallic character as well. To understand optical behavior calculations related to the important optical parameters; real and imaginary parts of the dielectric function, reflectivity R(ω), refractive index n(ω) and electron energy-loss function L(ω) have also been performed. In the present work, thermodynamically properties are also investigated by employing lattice vibrations integrated in quasi harmonic Debye model. Obtained results of volume, heat capacity and Debye temperature as a function of temperature for both compounds, at different values of pressure, are found to be consistent. The calculated value of melting temperature for both compounds (ScGa{sub 3} and Lu
Atomic carbon chains as spin-transmitters: An ab initio transport study
DEFF Research Database (Denmark)
Fürst, Joachim Alexander; Brandbyge, Mads; Jauho, Antti-Pekka
2010-01-01
An atomic carbon chain joining two graphene flakes was recently realized in a ground-breaking experiment by Jin et al. (Phys. Rev. Lett., 102 (2009) 205501). We present ab initio results for the electron transport properties of such chains and demonstrate complete spin-polarization of the transmi......An atomic carbon chain joining two graphene flakes was recently realized in a ground-breaking experiment by Jin et al. (Phys. Rev. Lett., 102 (2009) 205501). We present ab initio results for the electron transport properties of such chains and demonstrate complete spin...
Energy Technology Data Exchange (ETDEWEB)
Zhu, Xiaolei, E-mail: virtualzx@gmail.com; Yarkony, David R., E-mail: yarkony@jhu.edu [Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218 (United States)
2016-01-14
In this work, we demonstrate that for moderate sized systems, here a system with 13 atoms, global coupled potential energy surfaces defined for several electronic states over a wide energy range and for distinct regions of nuclear coordinate space characterized by distinct electron configurations, can be constructed with precise energetics and an excellent description of non-adiabatic interactions in all regions. This is accomplished using a recently reported algorithm for constructing quasi-diabatic representations, H{sup d}, of adiabatic electronic states coupled by conical intersections. In this work, the algorithm is used to construct an H{sup d} to describe the photodissociation of phenol from its first and second excited electronic states. The representation treats all 33 internal degrees of freedom in an even handed manner. The ab initio adiabatic electronic structure data used to construct the fit are obtained exclusively from multireference configuration interaction with single and double excitation wave functions comprised of 88 × 10{sup 6} configuration state functions, at geometries determined by quasi-classical trajectories. Since the algorithm uses energy gradients and derivative couplings in addition to electronic energies to construct H{sup d}, data at only 7379 nuclear configurations are required to construct a representation, which describes all nuclear configurations involved in H atom photodissociation to produce the phenoxyl radical in its ground or first excited electronic state, with a mean unsigned energy error of 202.9 cm{sup −1} for electronic energies <60 000 cm{sup −1}.
Hao, Changtong; Seymour, Jennifer L; Turecek, Frantisek
2007-09-13
Diaminohydroxymethyl (1) and triaminomethyl (2) radicals were generated by femtosecond collisional electron transfer to their corresponding cations (1+ and 2+, respectively) and characterized by neutralization-reionization mass spectrometry and ab initio/RRKM calculations at correlated levels of theory up to CCSD(T)/aug-cc-pVTZ. Ion 1+ was generated by gas-phase protonation of urea which was predicted to occur preferentially at the carbonyl oxygen with the 298 K proton affinity that was calculated as PA = 875 kJ mol-1. Upon formation, radical 1 gains vibrational excitation through Franck-Condon effects and rapidly dissociates by loss of a hydrogen atom, so that no survivor ions are observed after reionization. Two conformers of 1, syn-1 and anti-1, were found computationally as local energy minima that interconverted rapidly by inversion at one of the amine groups with a <7 kJ mol-1 barrier. The lowest energy dissociation of radical 1 was loss of the hydroxyl hydrogen atom from anti-1 with ETS = 65 kJ mol-1. The other dissociation pathways of 1 were a hydroxyl hydrogen migration to an amine group followed by dissociation to H2N-C=O* and NH3. Ion 2+ was generated by protonation of gas-phase guanidine with a PA = 985 kJ mol-1. Electron transfer to 2+ was accompanied by large Franck-Condon effects that caused complete dissociation of radical 2 by loss of an H atom on the experimental time scale of 4 mus. Radicals 1 and 2 were calculated to have extremely low ionization energies, 4.75 and 4.29 eV, respectively, which belong to the lowest among organic molecules and bracket the ionization energy of atomic potassium (4.34 eV). The stabilities of amino group containing methyl radicals, *CH2NH2, *CH(NH2)2, and 2, were calculated from isodesmic hydrogen atom exchange with methane. The pi-donating NH2 groups were found to increase the stability of the substituted methyl radicals, but the stabilities did not correlate with the radical ionization energies.
Energy Technology Data Exchange (ETDEWEB)
Guedj, C. [University Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054 Grenoble (France); Hung, L.; Sottile, F. [LSI, CNRS, CEA, École Polytechnique, F-91128 Palaiseau (France); European Theoretical Spectroscopy Facility (ETSF) (France); Zobelli, A. [LPS, CNRS and University Paris Sud, F-91405 Orsay (France); Blaise, P. [University Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054 Grenoble (France); European Theoretical Spectroscopy Facility (ETSF) (France); Olevano, V. [University Grenoble Alpes, F-38000 Grenoble (France); European Theoretical Spectroscopy Facility (ETSF) (France); CNRS, Institut Néel, F-38042 Grenoble (France)
2014-12-01
The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO{sub 2}) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO{sub 2}, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO{sub 2} may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectric permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors.
Guedj, C.; Hung, L.; Zobelli, A.; Blaise, P.; Sottile, F.; Olevano, V.
2014-12-01
The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO2) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO2, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO2 may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectric permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors.
Ab initio study of II-(VI){sub 2} dichalcogenides
Energy Technology Data Exchange (ETDEWEB)
Olsson, P; Vidal, J; Lincot, D, E-mail: polsson@kth.se [Institut de R and D sur l' energie photovoltaique (IRDEP), UMR 7174-EDF-CNRS-ENSCP, 6 quai Watier, 78401 Chatou Cedex (France)
2011-10-12
The structural stabilities of the (Zn,Cd)(S,Se,Te){sub 2} dichalcogenides have been determined ab initio. These compounds are shown to be stable in the pyrite phase, in agreement with available experiments. Structural parameters for the ZnTe{sub 2} pyrite semiconductor compound proposed here are presented. The opto-electronic properties of these dichalcogenide compounds have been calculated using quasiparticle GW theory. Bandgaps, band structures and effective masses are proposed as well as absorption coefficients and refraction indices. The compounds are all indirect semiconductors with very flat conduction band dispersion and high absorption coefficients. The work functions and surface properties are predicted. The Te and Se based compounds could be of interest as absorber materials in photovoltaic applications. (paper)
Ab initio study of alanine polypeptide chains twisting
Solovyov, I A; Solovyov, A V; Yakubovitch, A V; Greiner, Walter; Solov'yov, Andrey V.; Solov'yov, Ilia A.; Yakubovitch, Alexander V.
2005-01-01
We have investigated the potential energy surfaces for alanine chains consisting of three and six amino acids. For these molecules we have calculated potential energy surfaces as a function of the Ramachandran angles Phi and Psi, which are widely used for the characterization of the polypeptide chains. These particular degrees of freedom are essential for the characterization of proteins folding process. Calculations have been carried out within ab initio theoretical framework based on the density functional theory and accounting for all the electrons in the system. We have determined stable conformations and calculated the energy barriers for transitions between them. Using a thermodynamic approach, we have estimated the times of characteristic transitions between these conformations. The results of our calculations have been compared with those obtained by other theoretical methods and with the available experimental data extracted from the Protein Data Base. This comparison demonstrates a reasonable corres...
Institute of Scientific and Technical Information of China (English)
Jiang Ying; Zeng Zhi; Xia Shangda; Yin Min
2005-01-01
The electronic structures of LiYF4:Ce3+ and LiYF4 crystals simulated by an embedded (in a microcrystal containing 1938 ions) cluster CeY4Li8F24, and Y5Li8F24 respectively, were computed by the ab initio self-consistent relativistic DV-Xa(discrete variational Xa) method. The ground-state calculation showed that only the lowest 5d level Ed of Ce3+ ion lies around the BCB (bottom of the conduction band) while the lowest 4f levels is 2.5 eV lower than BCB. The CB states consist of 4p of Y mixed with 5d of Ce, even for the wavefunctions (WFS) of Ed under BCB there are still 24% of Y-4p and 9% of F-2p as components. Furthermore, transition state (TS) calculation was performed in this work to obtain the 4f→5d transition energies Efd, to improve the calculation of Ref.[6] in which a small CeF8 cluster embedded in an array of point charge was used and the results of ground-state calculation were roughly used to compare directly with the observed 4f→5d transition energies. The ionic radius of Ce3+ is larger than that of Y3+, for modeling approximately the lattice relaxation, we simply let the eight fluorine ions of the nearest-neighbor and next-nearest-neighbor move out radially and simultaneously. As results, the CeY4Li8F24 cluster with 4.56% outward relaxation of the eight fluorines has the lowest total energy and gave satisfactory 4f→5d energies Efd, but the calculated ground-state Ed is 0.68 eV higher than BCB. For another cluster with 7.36% outward relaxation the Ed is 0.43 eV lower than BCB, which makes the observation of fine structure (including zero-phonon line) of the lowest 5d band understandable easier, but the splits between the transition energies Efd were not as good as the former. Therefore, we consider the relaxation is somehow around 4.56%～7.36% outward, not as large as 10%.
Use of ab initio quantum chemical methods in battery technology
Energy Technology Data Exchange (ETDEWEB)
Deiss, E. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)
1997-06-01
Ab initio quantum chemistry can nowadays predict physical and chemical properties of molecules and solids. An attempt should be made to use this tool more widely for predicting technologically favourable materials. To demonstrate the use of ab initio quantum chemistry in battery technology, the theoretical energy density (energy per volume of active electrode material) and specific energy (energy per mass of active electrode material) of a rechargeable lithium-ion battery consisting of a graphite electrode and a nickel oxide electrode has been calculated with this method. (author) 1 fig., 1 tab., 7 refs.
Maschio, L.; Ferrabone, M.; Meyer, A.; Garza, J.; Dovesi, R.
2011-01-01
The performance of five different density functionals (LDA, PBE, PBESOL, B3LYP and PBE0) in describing the infrared spectrum of a crystalline periodic system with a large unit cell (spessartine, 80 atoms in the primitive cell) is studied by using the periodic ab initio CRYSTAL09 code and an all electron basis set. The transverse (TO) and longitudinal (LO) optical branches of the 17 IR active modes are evaluated together with the oscillator strengths and the high frequency dielectric tensor ɛ∞ . These ingredients permit to compute the dielectric function ɛ (ν) , and then the reflectance spectrum R (ν) , which is compared with experiment.
Lucas, J. M.; de Andrés, J.; López, E.; Albertí, M.; Bofill, J. M.; Bassi, D.; Ascenzi, D.; Tosi, P.; Aguilar, A.
2009-08-01
The association reactions between Li+, K+, and Rb+ (M) and butanone and cyclohexanone molecules under single collision conditions have been studied using a radiofrequency-guided ion-beam apparatus, characterizing the adducts by mass spectrometry. The excitation function for the [M-(molecule)]+ adducts (in arbitrary units) has been obtained at low collision energies in the 0.10 eV up to a few eV range in the center of mass frame. The measured relative cross sections decrease when collision energy increases, showing the expected energy dependence for adduct formation. The energetics and structure of the different adducts have been calculated ab initio at the MP2(full) level, showing that the M+-molecule interaction takes place through the carbonyl oxygen atom, as an example of a nontypical covalent chemical bond. The cross-section energy dependence and the role of radiative cooling rates allowing the stabilization of the collision complexes are also discussed.
Ab Initio Calculation on Self-Assembled Base-Functionalized Single-Walled Carbon Nanotubes
Institute of Scientific and Technical Information of China (English)
SONG Chen; XIA Yue-Yuan; ZHAO Ming-Wen; LIU Xiang-Dong; LI Ji-Ling; LI Li-Juan; LI Feng; HUANG Bo-Da
2006-01-01
@@ We perform ab initio calculations on the self-assembled base-functionalized single-walled carbon nanotubes (SWNTs) which exhibit the quasi-1D ‘ladder’ structure. The optimized configuration in the ab initio calculation is very similar to that obtainedfrom molecular dynamics simulation. We also calculate the electronic structures of the self-assembled base-functionalized SWNTs that exhibit distinct difference from the single-branch base-functionalized SWNT with a localized state lying just below the Fermi level, which may result from the coupling interaction between the bases accompanied by the self-assembly behaviour.
Setten, van M.J.; Wijs, de G.A.; Popa, V.A.; Brocks, G.
2005-01-01
Magnesium alanate Mg(AlH4)2 has recently raised interest as a potential material for hydrogen storage. We apply ab initio calculations to characterize structural, electronic and energetic properties of Mg(AlH4)2. Density functional theory calculations within the generalized gradient approximation (G
Relativistic ab initio spectroscopy study of forbidden lines of singly ionized zinc
Dixit, Gopal; Sahoo, Bijaya K.; Chaudhuri, Rajat K.; Majumder, Sonjoy
2009-01-01
The ab initio calculation has been carried out to study the astrophysically important forbidden electromagnetic transition rates of singly ionized zinc (Zn II). Electron correlations are considered to all orders using coupled-cluster theory in the relativistic framework. Calculated excitation energi
Ab initio and work function and surface energy anisotropy of LaB6
Uijttewaal, M. A.; de Wijs, G. A.; de Groot, R. A.
2006-01-01
Lanthanum hexaboride is one of the cathode materials most used in high-power electronics technology, but the many experimental results do not provide a consistent picture of the surface properties. Therefore, we report the first ab initio calculations of the work functions and surface energies of th
Energy Technology Data Exchange (ETDEWEB)
Dannenberg, Antje
2011-08-30
The mechanism which causes many of the unusual thermomechanical properties of martensitic alloys, as for example, superelasticity and the shape-memory effect, is the martensitic transformation. The prototype ferromagnetic shape memory alloy (FSMA) is Ni{sub 2}MnGa. But a technological breakthrough is missing due to its poor ductility and low operation temperatures. The goal of this thesis is the proposal of new FSMA appropriate for future technological applications. I focus on X{sub 2}YZ Heusler alloys which are mainly based on Mn, Fe, Co, and Ni for the X and Y sites and Z=Ga or Zn. The big challenge of this work is to find material classes which combine the unique magnetomechanical properties of FSMA which are large recoverable magnetostrictive strains, high magnetocrystalline anisotropy energy, and highly mobile twin boundaries with transformation temperatures clearly above room temperature and a reduced brittleness. Such a study, providing material classes which from a theoretical point of view are promising candidates for future FSMA, will help the experimental physicists to select interesting subgroups in the vast number of possible chemical compositions of X{sub 2}YZ Heusler alloys. I have systematically varied the composition in the new Heusler alloys in order to find trends indicating generic tendencies of the material properties, for instance, as a function of the valence electron concentration e/a. A main feature of this thesis is the attempt to find the origin of the competing structural ordering tendencies between conventional X{sub 2}YZ and inverse (XY)XZ Heusler structures which are observed for all systems investigated. In the first part of this work the accuracy and predictive power of ab initio and Monte Carlo simulations is demonstrated by reproducing the experimental phase diagram of Ni-Mn-(Ga,In,Sn,Sb). The linear increasing and decreasing slopes of T{sub M} and T{sub C} can be reproduced by total and free energy calculations and the analysis
Relaxation of Small Molecules: an ab initio Study
Institute of Scientific and Technical Information of China (English)
CAO Yi-Gang; JIAO Zheng-Kuan; A. Antons; K. Schroeder; S. Blügel2
2002-01-01
Using an ab initio total energy and force method, we have relaxed several group IV and group V elementalclusters, in detail the arsenic and antimony dimers, silicon, phosphorus, arsenic and antimony tetramers. The obtainedbond lengths and cohesive energies are more accurate than other calculating methods, and in excellent agreement withthe experimental results.
Resonance and Aromaticity : An Ab Initio Valence Bond Approach
Rashid, Zahid; van Lenthe, Joop H.; Havenith, Remco W. A.
2012-01-01
Resonance energy is one of the criteria to measure aromaticity. The effect of the use of different orbital models is investigated in the calculated resonance energies of cyclic conjugated hydrocarbons within the framework of the ab initio Valence Bond Self-Consistent Field (VBSCF) method. The VB wav
Structural flexibility of DABCO. Ab initio and DFT benchmark study
Nizovtsev, Anton S.; Ryzhikov, Maxim R.; Kozlova, Svetlana G.
2017-01-01
The energy and structural parameters of 1,4-diazabicyclo[2.2.2]octane (DABCO) obtained by various DFT methods are examined versus ab initio and experimental data. The features of twisting potentials of DABCO and closely-related species (1-azabicyclo[2.2.2]octane and bicyclo[2.2.2]octane) are discussed in light of computational schemes applied.
Properties of metals during the heating by intense laser irradiation using ab initio simulations
Holst, Bastian; Recoules, Vanina; Torrent, Marc; Mazevet, Stephane
2011-10-01
Ultrashort laser pulses irradiating a target heat the electrons to very high temperatures. In contrast, the ionic lattice is unaffected on the time scale of the laser pulse since the heat capacity of electrons is much smaller than that of the lattice. This non-equilibrium system can be described as a composition of two subsystems: one consisting of hot electrons and the other of an ionic lattice at low temperature. We studied the effect of this intense electronic excitations on the optical properties of gold using ab initio simulations. We additionally use ab initio linear response to compute the phonon spectrum and the electron-phonon coupling constant within Density Functional Theory for several electronic temperatures of few eV. LULI, Ecole Polytechnique, CNRS, CEA, UPMC, 91128 Palaiseau, France.
Ab initio simulations of pseudomorphic silicene and germanene bidimensional heterostructures
Debernardi, Alberto; Marchetti, Luigi
2016-06-01
Among the novel two-dimensional (2D) materials, silicene and germanene, which are two honeycomb crystal structures composed of a monolayer of Si and Ge, respectively, have attracted the attention of material scientists because they combine the advantages of the new 2D ultimate-scaled electronics with their compatibility with industrial processes presently based on Si and Ge. We envisage pseudomorphic lateral heterostructures based on ribbons of silicene and germanene, which are the 2D analogs of conventional 3D Si/Ge superlattices and quantum wells. In spite of the considerable lattice mismatch (˜4 % ) between free-standing silicene and germanene, our ab initio simulations predict that, considering striped 2D lateral heterostructures made by alternating silicene and germanene ribbons of constant width, the silicene/germanene junction remains pseudomorphic—i.e., it maintains lattice-matched edges—up to critical ribbon widths that can reach some tens of nanometers. Such critical widths are one order of magnitude larger than the critical thickness measured in 3D pseudomorphic Si/Ge heterostructures and the resolution of state-of-the-art lithography, thus enabling the possibility of lithography patterned silicene/germanene junctions. We computed how the strain produced by the pseudomorphic growth modifies the crystal structure and electronic bands of the ribbons, providing a mechanism for band-structure engineering. Our results pave the way for lithography patterned lateral heterostructures that can serve as the building blocks of novel 2D electronics.
Ab initio thermodynamic results for warm dense matter
Bonitz, Michael
2016-10-01
Warm dense matter (WDM) - an exotic state where electrons are quantum degenerate and ions may be strongly correlated - is ubiquitous in dense astrophysical plasmas and highly compressed laboratory systems including inertial fusion. Accurate theoretical predictions require precision thermodynamic data for the electron gas at high density and finite temperature around the Fermi temperature. First such data have been obtained by restricted path integral Monte Carlo (restricted PIMC) simulations and transformed into analytical fits for the free energy. Such results are also key input for novel finite temperature density functional theory. However, the RPIMC data of Ref. 1 are limited to moderate densities, and even there turned out to be surprisingly inaccurate, which is a consequence of the fermion sign problem. These problems were recently overcome by the development of alternative QMC approaches in Kiel (configuration PIMC and permutation blocking PIMC) and Imperial College (Density matrix QMC). The three methods have their strengths and limitations in complementary parameter regions and provide highly accurate thermodynamic data for the electronic contributions in WDM. While the original results were obtained for small particle numbers, recently accurate finite size corrections were derived allowing to compute ab initio thermodynamic data with an unprecedented accuracy of better than 0.3 percent. This provides the final step for the use as benchmark data for experiments and models of Warm dense matter. Co-authors: T. Schoof, S. Groth, T. Dornheim, F. D. Malone, M. Foulkes, and T. Sjostroem, Funded by: DFG via SFB-TR24 and project BO1366-10.
Energy Technology Data Exchange (ETDEWEB)
Ventelon, L. [CEA Saclay, Dept. des Materiaux pour le Nucleaire (DEN/DANS/DMN/SRMP), 91 - Gif-sur-Yvette (France)
2008-07-01
In the framework of the multi scale simulation of metals and alloys plasticity, the aim of this study is to develop a methodology of ab initio dislocations study and to apply it to the [111] screw dislocation in the bc iron. (A.L.B.)
Bannikov, V. V.; Beketov, A. R.; Baranov, M. V.; Elagin, A. A.; Kudyakova, V. S.; Shishkin, R. A.
2016-05-01
The phase stability, electronic structure, and magnetic properties of Al1- x Ti x N compositions based on the metastable aluminum nitride modification with the rock-salt structure at low ( x = 0.03) and high ( x = 0.25) concentrations of titanium in the system have been investigated using the results of ab initio band calculations. It has been shown that, at low values of x, the partial substitution is characterized by a positive enthalpy, which, however, changes sign with an increase in the titanium concentration. According to the results of the band structure calculations, the doped compositions have electronic conductivity. For x = 0.03, titanium impurity atoms have local magnetic moments (˜0.6 μB), and the electronic spectrum is characterized by a 100% spin polarization of near-Fermi states. Some of the specific features of the chemical bonding in Al1- x Ti x N cubic phases have been considered.
Ab-initio calculations for dilute magnetic semiconductors
Energy Technology Data Exchange (ETDEWEB)
Belhadji, Brahim
2008-03-03
This thesis focusses on ab-initio calculations for the electronic structure and the magnetic properties of dilute magnetic semiconductors (DMS). In particular we aim at the understanding of the complex exchange interactions in these systems. Our calculations are based on density functional theory, being ideally suited for a description of the material specific properties of the considered DMS. Moreover we use the KKR Green function method in connection with the coherent potential approximation (CPA), which allows to include the random substitutional disorder in a mean field-like approximation for the electronic structure. Finally we calculate the exchange coupling constants J{sub ij} between two impurities in a CPA medium by using the Lichtenstein formula and from this calculate the Curie temperature by a numerically exact Monte Carlo method. Based on this analysis we found and investigated four different exchange mechanisms being of importance in DMS systems: Double exchange, p-d exchange, antiferromagnetic superexchanges, and ferromagnetic superexchange. A second topic we have investigated in this thesis is the pressure dependence of the exchange interactions and the Curie temperatures in (Ga,Mn)As and (In,Mn)As, using the LDA and the LDA+U approximations. Exact calculations of T{sub C} by Monte Carlo simulations show a somehow different behavior. (orig.)
Ab initio modeling of decomposition in iron based alloys
Gorbatov, O. I.; Gornostyrev, Yu. N.; Korzhavyi, P. A.; Ruban, A. V.
2016-12-01
This paper reviews recent progress in the field of ab initio based simulations of structure and properties of Fe-based alloys. We focus on thermodynamics of these alloys, their decomposition kinetics, and microstructure formation taking into account disorder of magnetic moments with temperature. We review modern theoretical tools which allow a consistent description of the electronic structure and energetics of random alloys with local magnetic moments that become totally or partially disordered when temperature increases. This approach gives a basis for an accurate finite-temperature description of alloys by calculating all the relevant contributions to the Gibbs energy from first-principles, including a configurational part as well as terms due to electronic, vibrational, and magnetic excitations. Applications of these theoretical approaches to the calculations of thermodynamics parameters at elevated temperatures (solution energies and effective interatomic interactions) are discussed including atomistic modeling of decomposition/clustering in Fe-based alloys. It provides a solid basis for understanding experimental data and for developing new steels for modern applications. The precipitation in Fe-Cu based alloys, the decomposition in Fe-Cr, and the short-range order formation in iron alloys with s-p elements are considered as examples.
Ab initio calculations of the absorption spectrum of chalcone
Oumi, Manabu; Maurice, David; Head-Gordon, Martin
1999-03-01
The excitation energies and excited states of trans-chalcone ( trans-( s-cis)-1,3-diphenylpropenone), and several related molecules ( trans-( s-cis)-3-phenylpropenal, s-cis-1-phenylpropenone, propenal, trans-( s-cis)-1-(4-hydroxyphenyl)-3-phenylpropenone, trans-( s-cis)3-(4-hydroxyphenyl)-1-phenylpropenone) have been calculated using single reference ab initio molecular orbital methods, and characterized by attachment-detachment density analysis. The results suggest assignments for the lowest three electronic transitions observed experimentally for trans-( s-cis)-chalcone in solution. The extent of localization of the electronic transitions is established by calculations on the excited states of trans-( s-cis)-3-phenylpropenal, s-cis-1-phenylpropenone and propenal, as well as analysis of the chalcone calculations. Contrary to some previous work, none of these excitations are strongly delocalized over the entire molecule. Calculated substituent shifts for the hydroxy chalcones are in qualitative agreement with experimental data, and support the localized interpretation of the main π→ π* transition.
Ab initio molecular crystal structures, spectra, and phase diagrams.
Hirata, So; Gilliard, Kandis; He, Xiao; Li, Jinjin; Sode, Olaseni
2014-09-16
Conspectus Molecular crystals are chemists' solids in the sense that their structures and properties can be understood in terms of those of the constituent molecules merely perturbed by a crystalline environment. They form a large and important class of solids including ices of atmospheric species, drugs, explosives, and even some organic optoelectronic materials and supramolecular assemblies. Recently, surprisingly simple yet extremely efficient, versatile, easily implemented, and systematically accurate electronic structure methods for molecular crystals have been developed. The methods, collectively referred to as the embedded-fragment scheme, divide a crystal into monomers and overlapping dimers and apply modern molecular electronic structure methods and software to these fragments of the crystal that are embedded in a self-consistently determined crystalline electrostatic field. They enable facile applications of accurate but otherwise prohibitively expensive ab initio molecular orbital theories such as Møller-Plesset perturbation and coupled-cluster theories to a broad range of properties of solids such as internal energies, enthalpies, structures, equation of state, phonon dispersion curves and density of states, infrared and Raman spectra (including band intensities and sometimes anharmonic effects), inelastic neutron scattering spectra, heat capacities, Gibbs energies, and phase diagrams, while accounting for many-body electrostatic (namely, induction or polarization) effects as well as two-body exchange and dispersion interactions from first principles. They can fundamentally alter the role of computing in the studies of molecular crystals in the same way ab initio molecular orbital theories have transformed research practices in gas-phase physical chemistry and synthetic chemistry in the last half century. In this Account, after a brief summary of formalisms and algorithms, we discuss applications of these methods performed in our group as compelling
Ab initio calculation of the potential bubble nucleus 34Si
Duguet, T.; Somà, V.; Lecluse, S.; Barbieri, C.; Navrátil, P.
2017-03-01
the many-body correlations included in the calculation, is studied in detail. We eventually compare our predictions to state-of-the-art multireference energy density functional and shell model calculations. Results: The prediction regarding the (non)existence of the bubble structure in 34Si varies significantly with the nuclear Hamiltonian used. However, demanding that the experimental charge density distribution and the root-mean-square radius of 36S be well reproduced, along with 34Si and 36S binding energies, only leaves the NNLOsat Hamiltonian as a serious candidate to perform this prediction. In this context, a bubble structure, whose fingerprint should be visible in an electron scattering experiment of 34Si, is predicted. Furthermore, a clear correlation is established between the occurrence of the bubble structure and the weakening of the 1 /2--3 /2- splitting in the spectrum of 35Si as compared to 37S. Conclusions: The occurrence of a bubble structure in the charge distribution of 34Si is convincingly established on the basis of state-of-the-art ab initio calculations. This prediction will have to be reexamined in the future when improved chiral nuclear Hamiltonians are constructed. On the experimental side, present results act as a strong motivation to measure the charge density distribution of 34Si in future electron scattering experiments on unstable nuclei. In the meantime, it is of interest to perform one-neutron removal on 34Si and 36S in order to further test our theoretical spectral strength distributions over a wide energy range.
Das, Uday; Naskar, Jishu; Mukherjee, Alok Kumar
2015-12-01
A terminally protected acyclic tetrapeptide has been synthesized, and the crystal structure of its hydrated form, Boc-Tyr-Aib-Tyr-Ile-OMe·2H2O (1), has been determined directly from powder X-ray diffraction data. The backbone conformation of tetrapeptide (1) exhibiting two consecutive β-turns is stabilized by two 4 → 1 intramolecular N-H · · · O hydrogen bonds. In the crystalline state, the tetrapeptide molecules are assembled through water-mediated O-H · · · O hydrogen bonds to form two-dimensional molecular sheets, which are further linked by intermolecular C-H · · · O hydrogen bonds into a three-dimensional supramolecular framework. The molecular electrostatic potential (MEP) surface of (1) has been used to supplement the crystallographic observations. The nature of intermolecular interactions in (1) has been analyzed quantitatively through the Hirshfeld surface and two-dimensional fingerprint plot. The DFT optimized molecular geometry of (1) agrees closely with that obtained from the X-ray structure analysis. The present structure analysis of Boc-Tyr-Aib-Tyr-Ile-OMe·2H2 O (1) represents a case where ab-initio crystal structure of an acyclic tetrapeptide with considerable molecular flexibility has been accomplished from laboratory X-ray powder diffraction data.
McKemmish, Laura K; Tennyson, Jonathan
2016-01-01
Accurate knowledge of the rovibronic near-infrared and visible spectra of vanadium monoxide (VO) is very important for studies of cool stellar and hot planetary atmospheres. Here, the required ab initio dipole moment and spin-orbit coupling curves for VO are produced. This data forms the basis of a new VO line list considering 13 different electronic states and containing over 277 million transitions. Open shell transition, metal diatomics are challenging species to model through ab initio quantum mechanics due to the large number of low-lying electronic states, significant spin-orbit coupling and strong static and dynamic electron correlation. Multi-reference configuration interaction methodologies using orbitals from a complete active space self-consistent-field (CASSCF) calculation are the standard technique for these systems. We use different state-specific or minimal-state CASSCF orbitals for each electronic state to maximise the calculation accuracy. The off-diagonal dipole moment controls the intensity...
The Pu–U–Am system: An ab initio informed CALPHAD thermodynamic study
Energy Technology Data Exchange (ETDEWEB)
Perron, A., E-mail: perron1@llnl.gov [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Turchi, P.E.A.; Landa, A.; Söderlind, P. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Ravat, B.; Oudot, B.; Delaunay, F. [CEA-Centre de Valduc, 21120 Is sur Tille (France)
2015-03-15
Highlights: • The ab initio informed CALPHAD assessment of the Am–U system has been realized. • A strong tendency toward phase separation across the whole composition range is predicted. • The ab initio informed Pu–U–Am thermodynamic database has been developed. • The solubility of Am and U in the liquid phase is improved by adding Pu. • The δ-Pu (fcc) phase is strongly stabilized by Am, on the contrary to the bcc phase. - Abstract: Phase diagram and thermodynamic properties of the Am–U system, that are experimentally unknown, are calculated using the CALPHAD method with input from ab initio electronic-structure calculations for the fcc and bcc phases. A strong tendency toward phase separation across the whole composition range is predicted. In addition, ab initio informed Pu–U and Am–Pu thermodynamic assessments are combined to build a Pu–U–Am thermodynamic database. Regarding the Pu-rich corner of the ternary system, predictions indicate that Am acts as a powerful δ-Pu (fcc) stabilizer. In the U-rich corner, similar predictions are made but to a lesser extent. In both cases, the bcc phase is destabilized and the fcc phase is enhanced. Finally, results and methodology are discussed and compared with previous assessments and guidelines are provided for further experimental studies.
Spin-orbit decomposition of ab initio wavefunctions
Johnson, Calvin W
2014-01-01
Although the modern shell-model picture of atomic nuclei is built from single-particle orbits with good total angular momentum $j$, leading to $j$-$j$ coupling, phenomenological models suggested decades ago that for $0p$-shell nuclides a simpler picture can be realized via coupling of total spin $S$ and total orbital angular momentum $L$. I revisit this idea with large-basis, no-core shell model (NCSM) calculations using modern \\textit{ab initio} two-body interactions, and dissect the resulting wavefunctions into their component $L$- and $S$-components. Remarkably, there is broad agreement with calculations using the phenomenological Cohen-Kurath forces, despite a gap of nearly fifty years and six orders of magnitude in basis dimensions. I suggest $L$-$S$ may be a useful tool for analyzing \\textit{ab initio} wavefunctions of light nuclei, for example in the case of rotational bands.
Spin-orbit decomposition of ab initio nuclear wave functions
Johnson, Calvin W.
2015-03-01
Although the modern shell-model picture of atomic nuclei is built from single-particle orbits with good total angular momentum j , leading to j -j coupling, decades ago phenomenological models suggested that a simpler picture for 0 p -shell nuclides can be realized via coupling of the total spin S and total orbital angular momentum L . I revisit this idea with large-basis, no-core shell-model calculations using modern ab initio two-body interactions and dissect the resulting wave functions into their component L - and S -components. Remarkably, there is broad agreement with calculations using the phenomenological Cohen-Kurath forces, despite a gap of nearly 50 years and six orders of magnitude in basis dimensions. I suggest that L -S decomposition may be a useful tool for analyzing ab initio wave functions of light nuclei, for example, in the case of rotational bands.
Toward the Ab-initio Description of Medium Mass Nuclei
Barbieri, C; Soma, V; Duguet, T; Navratil, P
2012-01-01
As ab-initio calculations of atomic nuclei enter the A=40-100 mass range, a great challenge is how to approach the vast majority of open-shell (degenerate) isotopes. We add realistic three-nucleon interactions to the state of the art many-body Green's function theory of closed-shells, and find that physics of neutron driplines is reproduced with very good quality. Further, we introduce the Gorkov formalism to extend ab-initio theory to semi-magic, fully open-shell, isotopes. Proof-of-principle calculations for Ca-44 and Ni-74 confirm that this approach is indeed feasible. Combining these two advances (open-shells and three-nucleon interactions) requires longer, technical, work but it is otherwise within reach.
Serine Proteases an Ab Initio Molecular Dynamics Study
De Santis, L
1999-01-01
In serine proteases (SP's), the H-bond between His-57 and Asp-102, and that between Gly-193 and the transition state intermediate play a crucial role for enzymatic function. To shed light on the nature of these interactions, we have carried out ab initio molecular dynamics simulations on complexes representing adducts between the reaction intermediate and elastase (one protein belonging to the SP family). Our calculations indicate the presence of a low--barrier H-bond between His-57 and Asp-102, in complete agreement with NMR experiments on enzyme--transition state analog complexes. Comparison with an ab initio molecular dynamics simulation on a model of the substrate--enzyme adduct indicates that the Gly-193--induced strong stabilization of the intermediate is accomplished by charge/dipole interactions and not by H-bonding as previously suggested. Inclusion of the protein electric field in the calculations does not affect significantly the charge distribution.
The density matrix renormalization group for ab initio quantum chemistry
Wouters, Sebastian
2014-01-01
During the past 15 years, the density matrix renormalization group (DMRG) has become increasingly important for ab initio quantum chemistry. Its underlying wavefunction ansatz, the matrix product state (MPS), is a low-rank decomposition of the full configuration interaction tensor. The virtual dimension of the MPS, the rank of the decomposition, controls the size of the corner of the many-body Hilbert space that can be reached with the ansatz. This parameter can be systematically increased until numerical convergence is reached. The MPS ansatz naturally captures exponentially decaying correlation functions. Therefore DMRG works extremely well for noncritical one-dimensional systems. The active orbital spaces in quantum chemistry are however often far from one-dimensional, and relatively large virtual dimensions are required to use DMRG for ab initio quantum chemistry (QC-DMRG). The QC-DMRG algorithm, its computational cost, and its properties are discussed. Two important aspects to reduce the computational co...
Ab initio theories for light nuclei and neutron stars
Gezerlis, Alexandros
2016-09-01
In this talk I will touch upon several features of modern ab initio low-energy nuclear theory. I will start by discussing what ``ab initio'' means in this context. Specifically, I will spend some time going over nucleon-nucleon and three-nucleon interactions and their connections with the underlying theory of Quantum Chromodynamics. I will then show how these interactions are used to describe light nuclei using essentially exact few-body methods. I will then discuss heavier systems, especially those of astrophysical relevance, as well as the methods used to tackle them. This work was supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada and the Canada Foundation for Innovation (CFI).
Rational design of electrolyte components by ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Johansson, Patrik; Jacobsson, Per [Department of Applied Physics, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)
2006-02-28
This paper is a small review of the use of computer simulations and especially the use of standard quantum-mechanical ab initio electronic structure calculations to rationally design and investigate different choices of chemicals/systems for lithium battery electrolytes. Covered systems and strategies to enhance the performance of electrolytes will range from assisting the interpretation of vibrational spectroscopy experiments over development of potentials for molecular dynamics simulations, to the design of new lithium salts and the lithium ion coordination in liquid, polymer, and gel polymer electrolytes. Examples of studied properties include the vibrational spectra of anions and ion pairs to characterize the nature and extent of the interactions present, the lithium ion affinities of anions, important for the salt solvation and the ability to provide a high concentration of charge carriers, the HOMO energies of the anions to estimate the stability versus oxidation, the anion volumes that correlate to the anion mobility, the lithium ion coordination and dynamics to reveal the limiting steps of lithium ion transport, etc. (author)
Ab initio studies of niobium defects in uranium
Energy Technology Data Exchange (ETDEWEB)
Xiang, S; Huang, H; Hsiung, L
2007-06-01
Uranium (U), with the addition of small amount of niobium (Nb), is stainless. The Nb is fully miscible with the high temperature phase of U and tends to segregate upon cooling below 647 C. The starting point of segregation is the configuration of Nb substitutional or interstitial defects. Using density-functional-theory based ab initio calculations, the authors find that the formation energy of a single vacancy is 1.08 eV, that of Nb substitution is 0.59 eV, that of Nb interstitial at octahedral site is 1.58 eV, and that of Nb interstitial at tetrahedral site is 2.35 eV; all with reference to a reservoir of {gamma} phase U and pure Nb. The formation energy of Nb defects correlates with the local perturbation of electron distribution; higher formation energy to larger perturbation. Based on this study, Nb atoms thermodynamically prefer to occupy substitutional sites in {gamma} phase U, and they prefer to be in individual substitutional defects than clusters.
Ab initio modelling of boron related defects in amorphous silicon
Energy Technology Data Exchange (ETDEWEB)
Oliveira, Tiago A.; Torres, Vitor J.B. [Department of Physics, University of Aveiro, Campus Santiago, 3810-193 Aveiro (Portugal)
2012-10-15
We have modeled boron related point defects in amorphous silicon, using an ab initio method, the Density functional theory-pseudopotential code Aimpro. The boron atoms were embedded in 64 atom amorphous silicon cubic supercells. The calculations were performed using boron defects in 15 different supercells. These supercells were developed using a modified Wooten-Winer-Weaire bond switching mechanism. In average, the properties of the 15 supercells agree with the observed radial and bond angle distributions, as well the electronic and vibrational density of states and Raman spectra. In amorphous silicon it has been very hard to find real self-interstitials, since for almost all the tested configurations, the amorphous lattice relaxes overall. We found that substitutional boron prefers to be 4-fold coordinated. We find also an intrinsic hole-trap in the non-doped amorphous lattice, which may explain the low efficiency of boron doping. The local vibrational modes are, in average, higher than the correspondent crystalline values (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Nuclear forces and ab initio calculations of atomic nuclei
Meißner, Ulf-G.
2014-01-01
Nuclear forces and the nuclear many-body problem have been some of Gerry Brown's main topics in his so productive life as a theoretical physicist. In this talk, I outline how Gerry's work laid the foundations of the modern theory of nuclear forces and ab initio calculations of atomic nuclei. I also present some recent developments obtained in the framework of nuclear lattice simulations.
GAUSSIAN 76: An ab initio Molecular Orbital Program
Binkley, J. S.; Whiteside, R.; Hariharan, P. C.; Seeger, R.; Hehre, W. J.; Lathan, W. A.; Newton, M. D.; Ditchfield, R.; Pople, J. A.
1978-01-01
Gaussian 76 is a general-purpose computer program for ab initio Hartree-Fock molecular orbital calculations. It can handle basis sets involving s, p and d-type Gaussian functions. Certain standard sets (STO-3G, 4-31G, 6-31G*, etc.) are stored internally for easy use. Closed shell (RHF) or unrestricted open shell (UHF) wave functions can be obtained. Facilities are provided for geometry optimization to potential minima and for limited potential surface scans.
Ab Initio-Based Predictions of Hydrocarbon Combustion Chemistry
2015-07-15
144306 (2010)] and the cubic -‐ spline -‐fitted PES reported by Xu, Xie, Zhang, Lin, and Guo...SUBTITLE 13. SUPPLEMENTARY NOTES 12. DISTRIBUTION AVAILIBILITY STATEMENT 6. AUTHORS 7. PERFORMING ORGANIZATION NAMES AND ADDRESSES 15. SUBJECT TERMS b ...accurate global PESs and for direct dynamics simulations using interpolating moving least squares (IMLS) that guarantee high fidelity to ab initio data. A
Ab initio molecular dynamics using hybrid density functionals
Guidon, Manuel; Schiffmann, Florian; Hutter, Jürg; Vandevondele, Joost
2008-06-01
Ab initio molecular dynamics simulations with hybrid density functionals have so far found little application due to their computational cost. In this work, an implementation of the Hartree-Fock exchange is presented that is specifically targeted at ab initio molecular dynamics simulations of medium sized systems. We demonstrate that our implementation, which is available as part of the CP2K/Quickstep program, is robust and efficient. Several prescreening techniques lead to a linear scaling cost for integral evaluation and storage. Integral compression techniques allow for in-core calculations on systems containing several thousand basis functions. The massively parallel implementation respects integral symmetry and scales up to hundreds of CPUs using a dynamic load balancing scheme. A time-reversible multiple time step scheme, exploiting the difference in computational efficiency between hybrid and local functionals, brings further time savings. With extensive simulations of liquid water, we demonstrate the ability to perform, for several tens of picoseconds, ab initio molecular dynamics based on hybrid functionals of systems in the condensed phase containing a few thousand Gaussian basis functions.
Ab initio vibrations in nonequilibrium nanowires
DEFF Research Database (Denmark)
Jauho, Antti-Pekka; Engelund, Mads; Markussen, T
2010-01-01
We review recent results on electronic and thermal transport in two different quasi one-dimensional systems: Silicon nanowires (SiNW) and atomic gold chains. For SiNW's we compute the ballistic electronic and thermal transport properties on equal footing, allowing us to make quantitative predicti......We review recent results on electronic and thermal transport in two different quasi one-dimensional systems: Silicon nanowires (SiNW) and atomic gold chains. For SiNW's we compute the ballistic electronic and thermal transport properties on equal footing, allowing us to make quantitative...... predictions for the thermoelectric properties, while for the atomic gold chains we evaluate microscopically the damping of the vibrations, due to the coupling of the chain atoms to the modes in the bulk contacts. Both approaches are based on the combination of density-functional theory, and nonequilibrium...... Green's functions....
Energy Technology Data Exchange (ETDEWEB)
Bernard, St
1998-12-31
The quest for metallic hydrogen is a major goal for both theoretical and experimental condensed matter physics. Hydrogen and deuterium have been compressed up to 200 GPa in diamond anvil cells, without any clear evidence for a metallic behaviour. Loubeyere has recently suggested that hydrogen could metallize, at pressures within experimental range, in a new Van der Waals compound: Ar(H{sub 2}){sub 2} which is characterized at ambient pressure by an open and anisotropic sublattice of hydrogen molecules, stabilized by an argon skeleton. This thesis deals with a detailed ab initio investigation, by Car-Parrinello molecular dynamics methods, of the evolution under pressure of this compound. In a last chapter, we go to much higher pressures and temperatures, in order to compare orbital and orbital free ab initio methods for the dense hydrogen plasma. (author) 109 refs.
Lucas, José María; de Andrés, Jaime; Albertí, Margarita; Bofill, Josep Maria; Bassi, Davide; Aguilar, Antonio
2010-11-07
Reactive collisions between n-C(3)H(7)Cl molecules and lithium ions both in their ground electronic state have been studied in the 0.05-7.00 eV center of mass energy range using an octopole radio frequency guided-ion beam apparatus developed in our laboratory and recently modified. At low collision energies, dehydrohalogenation reactions leading to Li(C(3)H(6))(+) and Li(HCl)(+) are the main reaction channels, while on increasing energies C(3)H(7)(+) and C(2)H(3)(+) formation become dominant. Cross section energy dependences in arbitrary units for all these reactions have been measured. Also, ab initio electronic structure calculations at the MP2 level have been performed to obtain information about the potential energy surface on which the reactive processes take place. The reactants' entrance channel leads to the formation of a stable [Li-n-C(3)H(7)Cl](+) ion-molecule adduct that, following an intrinsic-reaction-coordinate pathway and surmounting a transition state, isomerizes to [Li-i-C(3)H(7)Cl](+). From this second minimum, dehydrohalogenation reactions for both n-C(3)H(7)Cl and i-C(3)H(7)Cl share a common reaction pathway leading to the same products. All potential barriers explored by reactions always lie below the reactants' energy. The entrance reaction channel [Li-n-C(3)H(7)Cl](+) adduct also leads adiabatically to C(3)H(7)(+) formation which, on increasing collision energy generates C(2)H(3)(+)via a unimolecular decomposition. A qualitative interpretation of the experimental results based on our ab initio calculations is also given.
Resonance and aromaticity: an ab initio valence bond approach.
Rashid, Zahid; van Lenthe, Joop H; Havenith, Remco W A
2012-05-17
Resonance energy is one of the criteria to measure aromaticity. The effect of the use of different orbital models is investigated in the calculated resonance energies of cyclic conjugated hydrocarbons within the framework of the ab initio Valence Bond Self-Consistent Field (VBSCF) method. The VB wave function for each system was constructed using a linear combination of the VB structures (spin functions), which closely resemble the Kekulé valence structures, and two types of orbitals, that is, strictly atomic (local) and delocalized atomic (delocal) p-orbitals, were used to describe the π-system. It is found that the Pauling-Wheland's resonance energy with nonorthogonal structures decreases, while the same with orthogonalized structures and the total mean resonance energy (the sum of the weighted off-diagonal contributions in the Hamiltonian matrix of orthogonalized structures) increase when delocal orbitals are used as compared to local p-orbitals. Analysis of the interactions between the different structures of a system shows that the resonance in the 6π electrons conjugated circuits have the largest contributions to the resonance energy. The VBSCF calculations also show that the extra stability of phenanthrene, a kinked benzenoid, as compared to its linear counterpart, anthracene, is a consequence of the resonance in the π-system rather than the H-H interaction in the bay region as suggested previously. Finally, the empirical parameters for the resonance interactions between different 4n+2 or 4n π electrons conjugated circuits, used in Randić's conjugated circuits theory or Herdon's semi-emprical VB approach, are quantified. These parameters have to be scaled by the structure coefficients (weights) of the contributing structures.
Ab Initio Calculations for the BaTiO3 (001) Surface Structure
Institute of Scientific and Technical Information of China (English)
XUE Xu-Yan; WANG Chun-Lei; ZHONG Wei-Lie
2004-01-01
@@ The ab initio method within the local density approximation is applied to calculate cubic BaTiO3 (001) surface relaxation and rumpling for two different terminations (BaO and TiO2). Our calculations demonstrate that cubic perovskite BaTiO3 crystals possess surface polarization, accompanied by the presence of the relevant electric field.We analyse their electronic structures (band structure, density of states and the electronic density redistribution with emphasis on the covalency effects). The results are also compared with that of the previous ab initio calculations. Considerable increases of Ti-O chemical bond covalency nearby the surface have been observed.The band gap reduces especially for the TiO2 termination.
Projector augmented wave method: ab initio molecular dynamics with full wave functions
Indian Academy of Sciences (India)
Peter E Blöchl; Clemens J Först; Johannes Schimpl
2003-01-01
A brief introduction to the projector augmented wave method is given and recent developments are reviewed. The projector augmented wave method is an all-electron method for efficient ab initio molecular dynamics simulations with full wave functions. It extends and combines the traditions of existing augmented wave methods and the pseudopotential approach. Without sacrificing efficiency, the PAW method avoids transferability problems of the pseudopotential approach and it has been valuable to predict properties that depend on the full wave functions.
Energy Technology Data Exchange (ETDEWEB)
Piskunov, S. [Institute of Solid State Physics, University of Latvia, Kengaraga 8, LV-1063 Riga (Latvia); Kotomin, E.A. [Institute of Solid State Physics, University of Latvia, Kengaraga 8, LV-1063 Riga (Latvia) and Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany)]. E-mail: kotomin@latnet.lv; Fuks, D. [Materials Engineering Department, Ben-Gurion University of the Negev, POB 653, Beer-Sheva (Israel); Dorfman, S. [Department of Physics, Technion- Israel Institute of Technology, Haifa 32000 (Israel)
2005-04-25
Understanding of the atomic and electronic structure of Ba{sub c}Sr{sub 1-c}TiO{sub 3} (BST) solid solutions is important for several applications including the non-volatile ferroelectric memories (dynamic random access memory, DRAM). We present results of ab initio calculations of several spatial arrangements of Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} solid solutions based on DFT-HF B3PW hybrid method. We calculate the atomic and electronic structure, the effective charges, interatomic bond populations, the electronic density distribution, and densities of states for three layered structures with the same composition. The suggested method reproduces experimental lattice parameters of both pure BaTiO{sub 3} and SrTiO{sub 3}. The calculated optical band gaps for the pure SrTiO{sub 3} and BaTiO{sub 3} are in a good agreement with experimental data, much better than those from the standard LDA or HF calculations. In the studied BST structures with the equiatomic composition (c = 0.5) the gap is reduced by ca. 0.2 eV. The electron density maps demonstrate the covalency effects in the Ti-O bonding. The electron density near the Sr atoms is stronger localized, as compared with the Ba ions.
Shiga, Motoyuki; Tachikawa, Masanori; Miura, Shinichi
2000-12-01
We present an accurate calculational scheme for many-body systems composed of electrons and nuclei, by path integral molecular dynamics technique combined with the ab initio molecular orbital theory. Based upon the scheme, the simulation of a water molecule at room temperature is demonstrated, applying all-electron calculation at the Hartree-Fock level of theory.
Kedziera, Dariusz; Mentel, Łukasz; Żuchowski, Piotr S.; Knoop, Steven
2015-06-01
We have obtained accurate ab initio +4Σ quartet potentials for the diatomic metastable triplet helium+alkali-metal (Li, Na, K, Rb) systems, using all-electron restricted open-shell coupled cluster singles and doubles with noniterative triples corrections CCSD(T) calculations and accurate calculations of the long-range C6 coefficients. These potentials provide accurate ab initio quartet scattering lengths, which for these many-electron systems is possible, because of the small reduced masses and shallow potentials that result in a small amount of bound states. Our results are relevant for ultracold metastable triplet helium+alkali-metal mixture experiments.
Spin-orbit decomposition of ab initio wavefunctions
Johnson, Calvin W.
2014-01-01
Although the modern shell-model picture of atomic nuclei is built from single-particle orbits with good total angular momentum $j$, leading to $j$-$j$ coupling, phenomenological models suggested decades ago that for $0p$-shell nuclides a simpler picture can be realized via coupling of total spin $S$ and total orbital angular momentum $L$. I revisit this idea with large-basis, no-core shell model (NCSM) calculations using modern \\textit{ab initio} two-body interactions, and dissect the resulti...
Accelerating Ab Initio Nuclear Physics Calculations with GPUs
Potter, Hugh; Maris, Pieter; Sosonkina, Masha; Vary, James; Binder, Sven; Calci, Angelo; Langhammer, Joachim; Roth, Robert; Çatalyürek, Ümit; Saule, Erik
2014-01-01
This paper describes some applications of GPU acceleration in ab initio nuclear structure calculations. Specifically, we discuss GPU acceleration of the software package MFDn, a parallel nuclear structure eigensolver. We modify the matrix construction stage to run partly on the GPU. On the Titan supercomputer at the Oak Ridge Leadership Computing Facility, this produces a speedup of approximately 2.2x - 2.7x for the matrix construction stage and 1.2x - 1.4x for the entire run.
Ab initio study of phase equilibria in TiCx
DEFF Research Database (Denmark)
Korzhavyi, P.A.; Pourovskii, L.V.; Hugosson, H.W.
2002-01-01
The phase diagram for the vacancy-ordered structures in the substoichiometric TiCx (x = 0.5-1.0) has been established from Monte Carlo simulations with the long-range pair and multisite effective interactions obtained from ab initio calculations. Three ordered superstructures of vacancies (Ti2C, Ti......3C2, and Ti6C5) are found to be ground state configurations. Their stability has been verified by full-potential total energy calculations of the fully relaxed structures....
Ab initio structure determination via powder X-ray diffraction
Indian Academy of Sciences (India)
Digamber G Porob; T N Guru Row
2001-10-01
Structure determination by powder X-ray diffraction data has gone through a recent surge since it has become important to get to the structural information of materials which do not yield good quality single crystals. Although the method of structure completion when once the starting model is provided is facile through the Rietveld refinement technique, the structure solution ab initio os still not push-button technology. In this article a survey of the recent development in this area is provided with an illustration of the structure determination of -NaBi3V2O10.
Ab initio modeling of small proteins by iterative TASSER simulations
Directory of Open Access Journals (Sweden)
Zhang Yang
2007-05-01
Full Text Available Abstract Background Predicting 3-dimensional protein structures from amino-acid sequences is an important unsolved problem in computational structural biology. The problem becomes relatively easier if close homologous proteins have been solved, as high-resolution models can be built by aligning target sequences to the solved homologous structures. However, for sequences without similar folds in the Protein Data Bank (PDB library, the models have to be predicted from scratch. Progress in the ab initio structure modeling is slow. The aim of this study was to extend the TASSER (threading/assembly/refinement method for the ab initio modeling and examine systemically its ability to fold small single-domain proteins. Results We developed I-TASSER by iteratively implementing the TASSER method, which is used in the folding test of three benchmarks of small proteins. First, data on 16 small proteins (α-root mean square deviation (RMSD of 3.8Å, with 6 of them having a Cα-RMSD α-RMSD α-RMSD of the I-TASSER models was 3.9Å, whereas it was 5.9Å using TOUCHSTONE-II software. Finally, 20 non-homologous small proteins (α-RMSD of 3.9Å was obtained for the third benchmark, with seven cases having a Cα-RMSD Conclusion Our simulation results show that I-TASSER can consistently predict the correct folds and sometimes high-resolution models for small single-domain proteins. Compared with other ab initio modeling methods such as ROSETTA and TOUCHSTONE II, the average performance of I-TASSER is either much better or is similar within a lower computational time. These data, together with the significant performance of automated I-TASSER server (the Zhang-Server in the 'free modeling' section of the recent Critical Assessment of Structure Prediction (CASP7 experiment, demonstrate new progresses in automated ab initio model generation. The I-TASSER server is freely available for academic users http://zhang.bioinformatics.ku.edu/I-TASSER.
Benchmarks of the ab initio FCI, MCSM and NCFC methods
Abe, T; Otsuka, T; Shimizu, N; Utsuno, Y; Vary, J P
2012-01-01
We report ab initio no-core solutions for properties of light nuclei with three different approaches in order to assess the accuracy and convergence rates of each method. Full Configuration Interaction (FCI), Monte Carlo Shell Model (MCSM) and No Core Full Configuration (NCFC) approaches are solved separately for the ground state energy and other properties of seven light nuclei using the realistic JISP16 nucleon-nucleon interaction. The results are consistent among the different approaches. The methods differ significantly in how the required computational resources scale with increasing particle number for a given accuracy.
Ab-initio study of transition metal hydrides
Energy Technology Data Exchange (ETDEWEB)
Sharma, Ramesh [Dept. of Physics, Feroze Gandhi Insititute of Engineering and Technology, Raebareli-229001 (India); Shukla, Seema, E-mail: sharma.yamini62@gmail.com; Dwivedi, Shalini, E-mail: sharma.yamini62@gmail.com; Sharma, Yamini, E-mail: sharma.yamini62@gmail.com [Theoretical Condensed Matter Physics Laboratory, Dept. of Physics Feroze Gandhi College, Raebareli-229001 (India)
2014-04-24
We have performed ab initio self consistent calculations based on Full potential linearized augmented plane wave (FP-LAPW) method to investigate the optical and thermal properties of yttrium hydrides. From the band structure and density of states, the optical absorption spectra and specific heats have been calculated. The band structure of Yttrium metal changes dramatically due to hybridization of Y sp orbitals with H s orbitals and there is a net charge transfer from metal to hydrogen site. The electrical resistivity and specific heats of yttrium hydrides are lowered but the thermal conductivity is slightly enhanced due to increase in scattering from hydrogen sites.
Tailoring magnetoresistance at the atomic level: An ab initio study
Tao, Kun
2012-01-05
The possibility of manipulating the tunneling magnetoresistance (TMR) of antiferromagnetic nanostructures is predicted in the framework of ab initio calculations. By the example of a junction composed of an antiferromagnetic dimer and a spin-polarized scanning tunneling microscopy tip we show that the TMR can be tuned and even reversed in sign by lateral and vertical movements of the tip. Moreover, our finite-bias calculations demonstrate that the magnitude and the sign of the TMR can also be tuned by an external voltage. © 2012 American Physical Society.
An ab initio potential function for the ν13 vibrational mode of 1,3-butadiene
Senent, M. L.
1995-06-01
The restricted potential of the ν13 torsional mode of 1,3-butadiene has been determined from ab initio calculations. The relative energy and geometry of the second rotamer were calculated with the optimized couple cluster method with double substitutions. This ab initio level provides that the second stable structure attaches to a gauche form situated at 140.8°. The potential energy function was obtained by fitting to a symmetry-adapted Fourier series the total electronic energies of several selected conformations. These energies were calculated by the Möller-Plesset perturbation theory up to the second order (MP2) with full and partial optimization of the geometry. Torsional Raman band positions and fundamental frequencies were determined from the periodic potentials with a good agreement with experimental data. The convenience of performing fully optimized calculations to determine the restricted function is also refuted.
Whitfield, T. W.; Crain, J.; Martyna, G. J.
2006-03-01
In order to better understand the physical interactions that stabilize protein secondary structure, the neat liquid state of a peptidic fragment, N-methylacetamide (NMA), was studied using computer simulation. Three different descriptions of the molecular liquid were examined: an empirical force field treatment with classical nuclei, an empirical force field treatment with quantum mechanical nuclei, and an ab initio density functional theory (DFT) treatment. The DFT electronic structure was evaluated using the BLYP approximate functional and a plane wave basis set. The different physical effects probed by the three models, such as quantum dispersion, many-body polarization, and nontrivial charge distributions on the liquid properties, were compared. Much of the structural ordering in the liquid is characterized by hydrogen bonded chains of NMA molecules. Modest structural differences are present among the three models of liquid NMA. The average molecular dipole in the liquid under the ab initio treatment, however, is enhanced by 60% over the gas phase value.
Melting of sodium under high pressure. An ab-initio study
Energy Technology Data Exchange (ETDEWEB)
González, D. J.; González, L. E. [Departamento de Física Teórica, Atómica y Optica, Universidad de Valladolid, 47011 Valladolid (Spain)
2015-08-17
We report ab-initio molecular dynamics simulations of dense liquid/solid sodium for a pressure range from 0 to 100 GPa. The simulations have been performed with the orbital free ab-initio molecular dynamics method which, by using the electron density as the basic variable, allows to perform simulations with large samples and for long runs. The calculated melting curve shows a maximum at a pressure ≈ 30 GPa and it is followed by a long, steep decrease. These features are in good agreement with the experimental data. For various pressures along the melting curve, we have calculated several liquid static properties (pair distribution functions, static structure factors and short-range order parameters) in order to analyze the structural effects of pressure.
Ab initio calculation of valley splitting in monolayer δ-doped phosphorus in silicon
Drumm, Daniel W.; Budi, Akin; Per, Manolo C.; Russo, Salvy P.; L Hollenberg, Lloyd C.
2013-02-01
The differences in energy between electronic bands due to valley splitting are of paramount importance in interpreting transport spectroscopy experiments on state-of-the-art quantum devices defined by scanning tunnelling microscope lithography. Using vasp, we develop a plane-wave density functional theory description of systems which is size limited due to computational tractability. Nonetheless, we provide valuable data for the benchmarking of empirical modelling techniques more capable of extending this discussion to confined disordered systems or actual devices. We then develop a less resource-intensive alternative via localised basis functions in siesta, retaining the physics of the plane-wave description, and extend this model beyond the capability of plane-wave methods to determine the ab initio valley splitting of well-isolated δ-layers. In obtaining an agreement between plane-wave and localised methods, we show that valley splitting has been overestimated in previous ab initio calculations by more than 50%.
Li ion diffusion mechanisms in LiFePO4: an ab initio molecular dynamics study.
Yang, Jianjun; Tse, John S
2011-11-17
The mechanisms for thermal (self) diffusion of Li ions in fully lithiated LiFePO(4) have been investigated with spin polarized ab initio molecular dynamics calculations. The effect of electron correlation is taken into account with the GGA+U formalism. It was found that Li ion diffusion is not a continuous process but through a series of jumps from one site to another. A dominant process is the hopping between neighboring Li sites around the PO(4) groups, which results in a zigzag pathway along the crystallographic b-axis. This observation is in agreement with a recent neutron diffraction experiment. A second process involves the collaborative movements of the Fe ions leading to the formation of antisite defects and promotes Li diffusion across the Li ion channels. The finding of the second mechanism demonstrates the benefit of ab initio molecular dynamics simulation in sampling diffusion pathways that may not be anticipated.
A highly accurate {\\it ab initio} potential energy surface for methane
Owens, Alec; Yachmenev, Andrey; Tennyson, Jonathan; Thiel, Walter
2016-01-01
A new nine-dimensional potential energy surface (PES) for methane has been generated using state-of-the-art \\textit{ab initio} theory. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit and incorporates a range of higher-level additive energy corrections. These include: core-valence electron correlation, higher-order coupled cluster terms beyond perturbative triples, scalar relativistic effects and the diagonal Born-Oppenheimer correction. Sub-wavenumber accuracy is achieved for the majority of experimentally known vibrational energy levels with the four fundamentals of $^{12}$CH$_4$ reproduced with a root-mean-square error of $0.70{\\,}$cm$^{-1}$. The computed \\textit{ab initio} equilibrium C{--}H bond length is in excellent agreement with previous values despite pure rotational energies displaying minor systematic errors as $J$ (rotational excitation) increases. It is shown that these errors can be significantly reduced by adjusting the e...
Liquid Be, Ca and Ba. An orbital-free ab-initio molecular dynamics study
Energy Technology Data Exchange (ETDEWEB)
Rio, B. G. del; González, L. E. [Departamento de Física Teórica, Atómica y Óptica, Universidad de Valladolid, 47011 Valladolid (Spain)
2015-08-17
Several static and dynamic properties of liquid beryllium (l-Be), liquid calcium (l-Ca) and liquid barium (l-Ba) near their triple point have been evaluated by the orbital-free ab initio molecular dynamics method (OF-AIMD), where the interaction between valence electrons and ions is described by means of local pseudopotentials. These local pseudopotentials used were constructed through a force-matching process with those obtained from a Kohn-Sham ab initio molecular dynamics study (KS-AIMD) of a reduced system with non-local pseudopotentials. The calculated static structures show good agreement with the available experimental data, including an asymmetric second peak in the structure factor which has been linked to the existence of a marked icosahedral short-range order in the liquid. As for the dynamic properties, we obtain collective density excitations whose associated dispersion relations exhibit a positive dispersion.
Ab initio calculations on the magnetic properties of transition metal complexes
Energy Technology Data Exchange (ETDEWEB)
Bodenstein, Tilmann; Fink, Karin [Karlsruhe Institute of Technology, Institute of Nanotechnology, POB 3640, 76021 Karlsruhe (Germany)
2015-12-31
We present a protocol for the ab initio determination of the magnetic properties of mono- and polynuclear transition metal compounds. First, we obtain the low lying electronic states by multireference methods. Then, we include spin-orbit coupling and an external magnetic field for the determination of zero-field splitting and g-tensors. For the polynuclear complexes the magnetic exchange coupling constants are determined by a modified complete active space self consistent field method. Based on the results of the ab initio calculations, magnetic data such as magnetic susceptibility or magnetization are simulated and compared to experimental data. The results obtained for the polynuclear complexes are further analysed by calculations on model complexes where part of the magnetic centers are substituted by diamagnetic ions. The methods are applied to different Co and Ni containing transition metal complexes.
Ab initio calculation of valley splitting in monolayer δ-doped phosphorus in silicon.
Drumm, Daniel W; Budi, Akin; Per, Manolo C; Russo, Salvy P; L Hollenberg, Lloyd C
2013-02-27
: The differences in energy between electronic bands due to valley splitting are of paramount importance in interpreting transport spectroscopy experiments on state-of-the-art quantum devices defined by scanning tunnelling microscope lithography. Using vasp, we develop a plane-wave density functional theory description of systems which is size limited due to computational tractability. Nonetheless, we provide valuable data for the benchmarking of empirical modelling techniques more capable of extending this discussion to confined disordered systems or actual devices. We then develop a less resource-intensive alternative via localised basis functions in siesta, retaining the physics of the plane-wave description, and extend this model beyond the capability of plane-wave methods to determine the ab initio valley splitting of well-isolated δ-layers. In obtaining an agreement between plane-wave and localised methods, we show that valley splitting has been overestimated in previous ab initio calculations by more than 50%.
Thermal transport in nanocrystalline Si and SiGe by ab initio based Monte Carlo simulation.
Yang, Lina; Minnich, Austin J
2017-03-14
Nanocrystalline thermoelectric materials based on Si have long been of interest because Si is earth-abundant, inexpensive, and non-toxic. However, a poor understanding of phonon grain boundary scattering and its effect on thermal conductivity has impeded efforts to improve the thermoelectric figure of merit. Here, we report an ab-initio based computational study of thermal transport in nanocrystalline Si-based materials using a variance-reduced Monte Carlo method with the full phonon dispersion and intrinsic lifetimes from first-principles as input. By fitting the transmission profile of grain boundaries, we obtain excellent agreement with experimental thermal conductivity of nanocrystalline Si [Wang et al. Nano Letters 11, 2206 (2011)]. Based on these calculations, we examine phonon transport in nanocrystalline SiGe alloys with ab-initio electron-phonon scattering rates. Our calculations show that low energy phonons still transport substantial amounts of heat in these materials, despite scattering by electron-phonon interactions, due to the high transmission of phonons at grain boundaries, and thus improvements in ZT are still possible by disrupting these modes. This work demonstrates the important insights into phonon transport that can be obtained using ab-initio based Monte Carlo simulations in complex nanostructured materials.
An ab initio study of plutonium oxides surfaces; Etude ab initio des surfaces d'oxydes de Pu
Energy Technology Data Exchange (ETDEWEB)
Jomard, G.; Bottin, F.; Amadon, B
2007-07-01
By means of first-principles calculations, we have studied the atomic structure as well as the thermodynamic stability of various plutonium dioxide surfaces in function of their environment (in terms of oxygen partial pressure and temperature). All these simulations have been performed with the ABINIT code. It is well known that DFT fails to describe correctly plutonium-based materials since 5f electrons in such systems are strongly correlated. In order to go beyond DFT, we have treated PuO{sub 2} and {beta}-Pu{sub 2}O{sub 3} in a DFT+U framework. We show that the couple of parameters (U,J) that works well for pure Pu is also well designed for describing ground state (GS) properties of these two oxides. The major improvement with respect with DFT is that we are able to predict an insulating GS in agreement with experiments. The presence of a gap in the DOS (Density of States) of plutonium oxides should play a significant role in the predicted surface reactivity. However, performing DFT+U calculations on surfaces of plutonium oxide from scratch was too ambitious. That is why we decided, as a first step, to study the stability of the (100), (110) and (111) surfaces of PuO{sub 2} in a DFT-GGA framework. For each of these orientations, we considered various terminations. These ab initio results have been introduced in a thermodynamic model which allows us to predict the relative stability of the different terminations as a function of temperature and oxygen partial pressure (p{sub O{sub 2}}). We conclude that at room temperature and for p{sub O{sub 2}}{approx}10 atm., the polar O{sub 2}-(100) termination is favoured. The stabilization of such a polar stoichiometric surface is surprising and should be confirmed by DFT+U calculations before any final conclusion. (authors)
First fully ab initio potential energy surface of methane with a spectroscopic accuracy
Nikitin, A. V.; Rey, M.; Tyuterev, Vl. G.
2016-09-01
Full 9-dimensional ab initio potential energy surfaces for the methane molecule are constructed using extended electronic structure coupled-cluster calculations with various series of basis sets following increasing X cardinal numbers: cc-pVXZ (X = 3, 4, 5, 6), aug-cc-ACVXZ (X = 3, 4, 5), and cc-pCVXZ-F12 (X = 3, 4). High-order dynamic electron correlations including triple and quadrupole excitations as well as relativistic and diagonal Born-Oppenheimer breakdown corrections were accounted for. Analytical potential functions are parametrized as non-polynomial expansions in internal coordinates in irreducible tensor representation. Vibrational energy levels are reported using global variational nuclear motion calculations with exact kinetic energy operator and a full account of the tetrahedral symmetry of CH4. Our best ab initio surface including above-mentioned contributions provides the rms (obs.-calc.) errors of less than 0.11 cm-1 for vibrational band centers below 4700 cm-1, and ˜0.3 cm-1 for all 229 assigned experimentally determined vibrational levels up to the Icosad range <7900 cm-1 without empirically adjusted parameters. These results improve the accuracy of ab initio methane vibrational predictions by more than an order of magnitude with respect to previous works. This is an unprecedented accuracy of first-principles calculations of a five-atomic molecule for such a large data set. New ab initio potential results in significantly better band center predictions even in comparison with best available empirically corrected potential energy surfaces. The issues related to the basis set extrapolation and an additivity of various corrections at this level of accuracy are discussed.
Unified ab initio approaches to nuclear structure and reactions
Navratil, Petr; Hupin, Guillaume; Romero-Redondo, Carolina; Calci, Angelo
2016-01-01
The description of nuclei starting from the constituent nucleons and the realistic interactions among them has been a long-standing goal in nuclear physics. In addition to the complex nature of the nuclear forces, with two-, three- and possibly higher many-nucleon components, one faces the quantum-mechanical many-nucleon problem governed by an interplay between bound and continuum states. In recent years, significant progress has been made in {\\em ab initio} nuclear structure and reaction calculations based on input from QCD-employing Hamiltonians constructed within chiral effective field theory. After a brief overview of the field, we focus on ab initio many-body approaches - built upon the No-Core Shell Model - that are capable of simultaneously describing both bound and scattering nuclear states, and present results for resonances in light nuclei, reactions important for astrophysics and fusion research. In particular, we review recent calculations of resonances in the $^6$He halo nucleus, of five- and six...
Ab Initio Thermodynamic Model for Magnesium Carbonates and Hydrates
Energy Technology Data Exchange (ETDEWEB)
Chaka, Anne M.; Felmy, Andrew R.
2014-03-28
An ab initio thermodynamic framework for predicting properties of hydrated magnesium carbonate minerals has been developed using density-functional theory linked to macroscopic thermodynamics through the experimental chemical potentials for MgO, water, and CO2. Including semiempirical dispersion via the Grimme method and small corrections to the generalized gradient approximation of Perdew, Burke, and Ernzerhof for the heat of formation yields a model with quantitative agreement for the benchmark minerals brucite, magnesite, nesquehonite, and hydromagnesite. The model shows how small differences in experimental conditions determine whether nesquehonite, hydromagnesite, or magnesite is the result of laboratory synthesis from carbonation of brucite, and what transformations are expected to occur on geological time scales. Because of the reliance on parameter-free first principles methods, the model is reliably extensible to experimental conditions not readily accessible to experiment and to any mineral composition for which the structure is known or can be hypothesized, including structures containing defects, substitutions, or transitional structures during solid state transformations induced by temperature changes or processes such as water, CO2, or O2 diffusion. Demonstrated applications of the ab initio thermodynamic framework include an independent means to evaluate differences in thermodynamic data for lansfordite, predicting the properties of Mg analogs of Ca-based hydrated carbonates monohydrocalcite and ikaite which have not been observed in nature, and an estimation of the thermodynamics of barringtonite from the stoichiometry and a single experimental observation.
Ab initio thermodynamic model for magnesium carbonates and hydrates.
Chaka, Anne M; Felmy, Andrew R
2014-09-04
An ab initio thermodynamic framework for predicting properties of hydrated magnesium carbonate minerals has been developed using density-functional theory linked to macroscopic thermodynamics through the experimental chemical potentials for MgO, water, and CO2. Including semiempirical dispersion via the Grimme method and small corrections to the generalized gradient approximation of Perdew, Burke, and Ernzerhof for the heat of formation yields a model with quantitative agreement for the benchmark minerals brucite, magnesite, nesquehonite, and hydromagnesite. The model shows how small differences in experimental conditions determine whether nesquehonite, hydromagnesite, or magnesite is the result of laboratory synthesis from carbonation of brucite, and what transformations are expected to occur on geological time scales. Because of the reliance on parameter-free first-principles methods, the model is reliably extensible to experimental conditions not readily accessible to experiment and to any mineral composition for which the structure is known or can be hypothesized, including structures containing defects, substitutions, or transitional structures during solid state transformations induced by temperature changes or processes such as water, CO2, or O2 diffusion. Demonstrated applications of the ab initio thermodynamic framework include an independent means to evaluate differences in thermodynamic data for lansfordite, predicting the properties of Mg analogues of Ca-based hydrated carbonates monohydrocalcite and ikaite, which have not been observed in nature, and an estimation of the thermodynamics of barringtonite from the stoichiometry and a single experimental observation.
Energy Technology Data Exchange (ETDEWEB)
Benkhelifa, F.Z.; Lekhal, A.; Méçabih, S., E-mail: mecabihsa@yahoo.com; Abbar, B.; Bouhafs, B.
2014-12-15
We have investigated the electronic structure, magnetic and thermal properties of the ternary full-Heusler alloys Rh{sub 2}MnZ (Z=Ge, Sn, Pb) under pressure employing the full potential linearized augmented plane wave (FP-LAPW) plus local orbitals method based on the density functional theory (DFT), For the exchange–correlation effects we have adopted the generalized gradient approximation (GGA).Through the quasi-harmonic Debye model, we also study the thermodynamic properties of Rh{sub 2}MnZ (Z=Ge, Sn and Pb). The thermal expansion versus temperature and pressure, the thermodynamic parameters (Debye temperature and specific heat) with pressure P, and the heat capacity at various pressures and temperatures in the ranges of 0 GPa to 0.6 GPa and 0 K to 400 K have been obtained. - Highlights: • Ab-initio study of the electronic properties of Rh{sub 2}MnZ (Z=Ge, Sn, Pb). • Thermodynamic properties of Rh{sub 2}MnZ (Z=Ge, Sn and Pb) are predicted. • Pressure effect on the structural and electronic properties. • The effect of temperature and pressure on the Debye temperature.
Eremeev, S V; Chukurov, E N; Gruznev, D V; Zotov, A V; Saranin, A A
2015-08-05
Using ab initio calculations, atomic structure and electronic properties of Si(1 1 1)[Formula: see text]-Bi surface modified by adsorption of 1/3 monolayer of alkali metals, Li, Na, K, Rb and Cs, have been explored. Upon adsorption of all metals, a similar atomic structure develops at the surface where twisted chained Bi trimers are arranged into a honeycomb network and alkali metal atoms occupy the [Formula: see text] sites in the center of each honeycomb unit. Among other structural characteristics, the greatest variation concerns the relative heights at which alkali metals reside with respect to Bi-trimer layer. Except for Li, the other metals reside higher than Bi layer and their heights increase with atomic number. All adsorbed surface structures display similar electron band structures of which the most essential feature is metallic surface-state band with a giant spin splitting. This electronic property allows one to consider the Si(1 1 1)[Formula: see text]-Bi surfaces modified by alkali metal adsorption as a set of material systems showing promise for spintronic applications.
Eremeev, S. V.; Chukurov, E. N.; Gruznev, D. V.; Zotov, A. V.; Saranin, A. A.
2015-08-01
Using ab initio calculations, atomic structure and electronic properties of Si(1 1 1)\\sqrt{3}× \\sqrt{3} -Bi surface modified by adsorption of 1/3 monolayer of alkali metals, Li, Na, K, Rb and Cs, have been explored. Upon adsorption of all metals, a similar atomic structure develops at the surface where twisted chained Bi trimers are arranged into a honeycomb network and alkali metal atoms occupy the {{T}4} sites in the center of each honeycomb unit. Among other structural characteristics, the greatest variation concerns the relative heights at which alkali metals reside with respect to Bi-trimer layer. Except for Li, the other metals reside higher than Bi layer and their heights increase with atomic number. All adsorbed surface structures display similar electron band structures of which the most essential feature is metallic surface-state band with a giant spin splitting. This electronic property allows one to consider the Si(1 1 1)\\sqrt{3}× \\sqrt{3} -Bi surfaces modified by alkali metal adsorption as a set of material systems showing promise for spintronic applications.
Energy Technology Data Exchange (ETDEWEB)
Sandoghchi, M. [Advanced Materials Laboratory (AML), Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of); Khosroabadi, H., E-mail: khosroabadi@sharif.edu [Advanced Materials Laboratory (AML), Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of); Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365-916, Tehran (Iran, Islamic Republic of); Akhavan, M. [Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365-916, Tehran (Iran, Islamic Republic of)
2014-12-15
Highlights: • The lattice parameters changes by K doping is explained by ionic charge and the metal–metal bonding scenario. • Creation of a larger peak near the Fermi level and increase the DOS at the Fermi level by K doping. • The effects of K on DOS has been related to the magnetic transition, change of the lattice parameters and FeAs{sub 4} tetrahedron. • Investigation of the number of Fermi level crossed bands by K doping and the band changes near the Fermi level. - Abstract: The crystal and electronic structures of normal phase of Ba{sub 1−x}K{sub x}Fe{sub 2}As{sub 2} for x = 0.0, 0.5 and 1.0 have been studied by using pseudopotential Quantum Espresso code based on ab-initio density functional theory. Effects of K doping on the crystal structure and lattice parameters have been calculated and compared with the experimental and computational reported data for similar compounds. The metal–metal bonding scenario was used to explain the changes of lattice parameters by K doping. The electronic structure of this system including of density of states and band structure have been calculated and investigated by K doping. One of the interesting results is that a larger peak is appeared near the Fermi level by increasing of the K doping. These changes could produce a potential for creation of the superconducting state in this system.
Ab initio studies of ionization potentials of hydrated hydroxide and hydronium
Swartz, Charles W
2013-01-01
The ionization potential distributions of hydrated hydroxide and hydronium are computed with many-body approach for electron excitations with configurations generated by {\\it ab initio} molecular dynamics. The experimental features are well reproduced and found to be closely related to the molecular excitations. In the stable configurations, the ionization potential is mainly perturbed by water molecules within the first solvation shell. On the other hand, electron excitation is delocalized on both proton receiving and donating complex during proton transfer, which shifts the excitation energies and broadens the spectra for both hydrated ions.
Charge carrier motion in disordered conjugated polymers: a multiscale ab-initio study
Energy Technology Data Exchange (ETDEWEB)
Vukmirovic, Nenad; Wang, Lin-Wang
2009-11-10
We developed an ab-initio multiscale method for simulation of carrier transport in large disordered systems, based on direct calculation of electronic states and electron-phonon coupling constants. It enabled us to obtain the never seen before rich microscopic details of carrier motion in conjugated polymers, which led us to question several assumptions of phenomenological models, widely used in such systems. The macroscopic mobility of disordered poly(3- hexylthiophene) (P3HT) polymer, extracted from our simulation, is in agreement with experimental results from the literature.
Ab initio study of spin-dependent transport in carbon nanotubes with iron and vanadium adatoms
DEFF Research Database (Denmark)
Fürst, Joachim Alexander; Brandbyge, Mads; Jauho, Antti-Pekka
2008-01-01
We present an ab initio study of spin-dependent transport in armchair carbon nanotubes with transition metal adsorbates: iron or vanadium. The method based on density functional theory and nonequilibrium Green's functions is used to compute the electronic structure and zero-bias conductance....... The presence of the adsorbate causes scattering of electrons of mainly one spin type. The scattering is shown to be due to a coupling of the two armchair band states to the metal 3d orbitals with matching symmetry, giving rise to Fano antiresonances appearing as dips in the transmission function. The spin type...
Improved Ab Initio Molecular Dynamics by Minimal Biasing with Experimental Data
White, Andrew D; Hocky, Glen M; Voth, Gregory A
2016-01-01
Accounting for electrons and nuclei simultaneously is a key goal of computer simulation via ab initio molecular dynamics (AIMD). However, AIMD is often unable to accurately reproduce the properties of systems such as water due to inaccuracies in the underlying electronic density functionals, shortcomings that are often addressed by added empirical corrections and/or increasing the simulation temperature. We present here a maximum-entropy-based approach to directly incorporate limited experimental data via a minimal bias. The biased AIMD simulations of both water and of an excess proton in water are shown to give significantly improved properties for both the biased and unbiased observables.
Ohta, Yasuhito; Ohta, Koji; Kinugawa, Kenichi
2004-01-01
An ab initio centroid molecular dynamics (CMD) method is developed by combining the CMD method with the ab initio molecular orbital method. The ab initio CMD method is applied to vibrational dynamics of diatomic molecules, H2 and HF. For the H2 molecule, the temperature dependence of the peak frequency of the vibrational spectral density is investigated. The results are compared with those obtained by the ab initio classical molecular dynamics method and exact quantum mechanical treatment. It is shown that the vibrational frequency obtained from the ab initio CMD approaches the exact first excitation frequency as the temperature lowers. For the HF molecule, the position autocorrelation function is also analyzed in detail. The present CMD method is shown to well reproduce the exact quantum result for the information on the vibrational properties of the system.
Quantum plasmonics: from jellium models to ab initio calculations
Directory of Open Access Journals (Sweden)
Varas Alejandro
2016-08-01
Full Text Available Light-matter interaction in plasmonic nanostructures is often treated within the realm of classical optics. However, recent experimental findings show the need to go beyond the classical models to explain and predict the plasmonic response at the nanoscale. A prototypical system is a nanoparticle dimer, extensively studied using both classical and quantum prescriptions. However, only very recently, fully ab initio time-dependent density functional theory (TDDFT calculations of the optical response of these dimers have been carried out. Here, we review the recent work on the impact of the atomic structure on the optical properties of such systems. We show that TDDFT can be an invaluable tool to simulate the time evolution of plasmonic modes, providing fundamental understanding into the underlying microscopical mechanisms.
An Efficient Approach to Ab Initio Monte Carlo Simulation
Leiding, Jeff
2013-01-01
We present a Nested Markov Chain Monte Carlo (NMC) scheme for building equilibrium averages based on accurate potentials such as density functional theory. Metropolis sampling of a reference system, defined by an inexpensive but approximate potential, is used to substantially decorrelate configurations at which the potential of interest is evaluated, thereby dramatically reducing the number needed to build ensemble averages at a given level of precision. The efficiency of this procedure is maximized on-the-fly through variation of the reference system thermodynamic state (characterized here by its inverse temperature \\beta^0), which is otherwise unconstrained. Local density approximation (LDA) results are presented for shocked states in argon at pressures from 4 to 60 GPa. Depending on the quality of the reference potential, the acceptance probability is enhanced by factors of 1.2-28 relative to unoptimized NMC sampling, and the procedure's efficiency is found to be competitive with that of standard ab initio...
Ab initio quantum dynamics using coupled-cluster
Kvaal, Simen
2012-01-01
The curse of dimensionality (COD) limits the current state-of-the-art {\\it ab initio} propagation methods for non-relativistic quantum mechanics to relatively few particles. For stationary structure calculations, the coupled-cluster (CC) method overcomes the COD in the sense that the method scales polynomially with the number of particles while still being size-consistent and extensive. We generalize the CC method to the time domain while allowing the single-particle functions to vary in an adaptive fashion as well, thereby creating a highly flexible, polynomially scaling approximation to the time-dependent Schr\\"odinger equation. The method inherits size-consistency and extensivity from the CC method. The method is dubbed orbital-adaptive time-dependent coupled-cluster (OATDCC), and is a hierarchy of approximations to the now standard multi-configurational time-dependent Hartree method for fermions. A numerical experiment is also given.
Ab initio study of the transition-metal carbene cations
Institute of Scientific and Technical Information of China (English)
李吉海; 冯大诚; 冯圣玉
1999-01-01
The geometries and bonding characteristics of the first-row transition-metal carbene cations MCH2+ were investigated by ab initio molecular orbital theory （HF/LANL2DZ）. All of MCH2+ are coplanar. In the closed shell structures the C bonds to M with double bonds; while in the open shell structures the partial double bonds are formed, because one of the σ and π orbitals is singly occupied. It is mainly the π-type overlap between the 2px orbital of C and 4px, 3dxz, orbitals of M+ that forms the π orbitals. The dissociation energies of C—M bond appear in periodic trend from Sc to Cu. Most of the calculated bond dissociation energies are close to the experimental ones.
Ab initio and kinetic modeling studies of formic acid oxidation
DEFF Research Database (Denmark)
Marshall, Paul; Glarborg, Peter
2015-01-01
A detailed chemical kinetic model for oxidation of formic acid (HOCHO) in flames has been developed, based on theoretical work and data from literature. Ab initio calculations were used to obtain rate coefficients for reactions of HOCHO with H, O, and HO2. Modeling predictions with the mechanism...... have been compared to the experimental results of de Wilde and van Tiggelen (1968) who measured the laminar burning velocities for HOCHO flames over a range of stoichiometries and dilution ratios. The modeling predictions are generally satisfactory. The governing reaction mechanisms are outlined based...... on calculations with the kinetic model. Formic acid is consumed mainly by reaction with OH, yielding OCHO, which dissociates rapidly to CO2 + H, and HOCO, which may dissociate to CO + OH or CO2 + H, or react with H, OH, or O2 to form more stable products. The branching fraction of the HOCHO + OH reaction, as well...
Ab initio investigation of the mechanical properties of copper
Institute of Scientific and Technical Information of China (English)
Liu Yue-Lin; Gui Li-Jiang; Jin Shuo
2012-01-01
Employing the ab initio total energy method based on the density functional theory with the generalized gradient approximation,we have systematically investigated the theoretical mechanical properties of copper (Cu).The theoretical tensile strengths are calculated to be 25.3 GPa,5.9 GPa,and 37.6 GPa for the fcc Cu single crystal in the [001],[110],and [111] directions,respectively.Among the three directions,the [110] direction is the weakest one due to the occurrence of structure transition at the lower strain and the weakest interaction of atoms between the (110) planes,while the [111] direction is the strongest direction because of the strongest interaction of atoms between the (111) planes.In terms of the elastic constants of Cu single crystal,we also estimate some mechanical quantities of polycrystalline Cu,including bulk modulus B,shear modulus G,Young's modulus Ep,and Poisson's ratio v.
Ab initio quantum dynamics using coupled-cluster.
Kvaal, Simen
2012-05-21
The curse of dimensionality (COD) limits the current state-of-the-art ab initio propagation methods for non-relativistic quantum mechanics to relatively few particles. For stationary structure calculations, the coupled-cluster (CC) method overcomes the COD in the sense that the method scales polynomially with the number of particles while still being size-consistent and extensive. We generalize the CC method to the time domain while allowing the single-particle functions to vary in an adaptive fashion as well, thereby creating a highly flexible, polynomially scaling approximation to the time-dependent Schrödinger equation. The method inherits size-consistency and extensivity from the CC method. The method is dubbed orbital-adaptive time-dependent coupled-cluster, and is a hierarchy of approximations to the now standard multi-configurational time-dependent Hartree method for fermions. A numerical experiment is also given.
Ab initio Molecular Dynamics Study on Small Carbon Nanotubes
Institute of Scientific and Technical Information of China (English)
叶林晖; 刘邦贵; 王鼎盛
2001-01-01
Ab initio molecular dynamics simulations are performed on small single wall nanotubes. By structural relaxation,the equilibrium C-C bond lengths and bond angles are determined. Our result shows that for both zigzag and armchair nanotubes there are two nonequivalent bond lengths. One bond stretches from that of the graphene sheet, while the other shrinks. Small variations on bond angles are also shown. Energy bands are calculated for the optimized structures. It is found that the intrinsic curvature of the very small nanotube greatly modifies the energy band which can no longer be well described in the tight-binding zone-folding picture. In our calculation very small nanotubes are metallic. The energy per atom fits quite well with the relation of E(R) = E0 + f/R2 even for the extreme small radius. The implications of the results on the properties of small nanotubes are discussed.
High-throughput ab-initio dilute solute diffusion database
Wu, Henry; Mayeshiba, Tam; Morgan, Dane
2016-07-01
We demonstrate automated generation of diffusion databases from high-throughput density functional theory (DFT) calculations. A total of more than 230 dilute solute diffusion systems in Mg, Al, Cu, Ni, Pd, and Pt host lattices have been determined using multi-frequency diffusion models. We apply a correction method for solute diffusion in alloys using experimental and simulated values of host self-diffusivity. We find good agreement with experimental solute diffusion data, obtaining a weighted activation barrier RMS error of 0.176 eV when excluding magnetic solutes in non-magnetic alloys. The compiled database is the largest collection of consistently calculated ab-initio solute diffusion data in the world.
Energy Technology Data Exchange (ETDEWEB)
Yao, Yongxin [Iowa State Univ., Ames, IA (United States)
2009-01-01
also plays an important role, as it may directly track the movement of every atom. Simulation time is a major limit for molecular dynamics, not only because of “slow” computer speed, but also because of the accumulation error in the numerical treatment of the motion equations. There is also a great concern about the reliability of the emperical potentials if using classical molecular dynamics. Ab initio methods based on density functional theory(DFT) do not have this problem, however, it suffers from small simulation cells and is more demanding computationally. When crystal phase is involved, size effect of the simulation cell is more pronounced since long-range elastic energy would be established. Simulation methods which are more efficient in computation but yet have similar reliability as the ab initio methods, like tight-binding method, are highly desirable. While the complexity of metallic glasses comes from the atomistic level, there is also a large field which deals with the complexity from electronic level. The only “ab initio” method applicable to solid state systems is density functional theory with local density approximation( LDA) or generalized gradient approximation(GGA) for the exchange-correlation energy. It is very successful for simple sp element, where it reaches an high accuracy for determining the surface reconstruction. However, there is a large class of materials with strong electron correlation, where DFT based on LDA or GGA fails in a fundamental way. An “ab initio” method which can generally apply to correlated materials, as LDA for simple sp element, is still to be developed. The thesis is prepared to address some of the above problems.
Bannikov, V. V.; Ivanovskii, A. L.
2013-12-01
Very recently, on the example of hole- and spin-doped semiconductor LaZnAsO, quite an unexpected area of potential applications of quasi-two-dimensional 1111-like phases was proposed (C. Ding et al., Phys. Rev. B 88, 041102R (2013)) as a promising platform for searching for new diluted magnetic semiconductors (DMSs). In this work, by means of the ab initio calculations, we have examined in detail the electronic and magnetic properties of LaZnAsO alloyed with Ba and Mn. Our results demonstrate that Ba or Mn doping transforms the parent non-magnetic semiconductor LaZnAsO into a non-magnetic metal or a magnetic semiconductor, respectively. On the other hand, the joint effect of these dopants (i.e., co-doping Ba + Mn) leads to transition of La0.89Ba0.11Zn0.89Mn0.11AsO into the state of magnetic metal, which is formed by alternately stacked semiconducting non-magnetic blocks [La0.89Ba0.11O] and metallic-like magnetic blocks [Zn0.89Mn0.11As].
Ab initio quantum Monte Carlo calculations of ground-state properties of manganese's oxides
Sharma, Vinit; Krogel, Jaron T.; Kent, P. R. C.; Reboredo, Fernando A.
One of the critical scientific challenges of contemporary research is to obtain an accurate theoretical description of the electronic properties of strongly correlated systems such as transition metal oxides and rare-earth compounds, since state-of-art ab-initio methods based on approximate density functionals are not always sufficiently accurate. Quantum Monte Carlo (QMC) methods, which use statistical sampling to evaluate many-body wave functions, have the potential to answer this challenge. Owing to the few fundamental approximations made and the direct treatment of electron correlation, QMC methods are among the most accurate electronic structure methods available to date. We assess the accuracy of the diffusion Monte Carlo method in the case of rocksalt manganese oxide (MnO). We study the electronic properties of this strongly-correlated oxide, which has been identified as a suitable candidate for many applications ranging from catalysts to electronic devices. ``This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.'' Ab initio quantum Monte Carlo calculations of ground-state properties of manganese's oxides.
Atomic ionization of germanium by neutrinos from an ab initio approach
Energy Technology Data Exchange (ETDEWEB)
Chen, Jiunn-Wei [Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China); National Center for Theoretical Sciences and Leung Center for Cosmology and Particle Astrophysics, National Taiwan University, Taipei 10617, Taiwan (China); Chi, Hsin-Chang [Department of Physics, National Dong Hwa University, Shoufeng, Hualien 97401, Taiwan (China); Huang, Keh-Ning [Department of Physics, Sichuan University, Chengdu, Sichuan (China); Department of Physics, Fuzhou University, Fuzhou, Fujian (China); Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China); Liu, C.-P. [Department of Physics, National Dong Hwa University, Shoufeng, Hualien 97401, Taiwan (China); Shiao, Hao-Tse [Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China); Singh, Lakhwinder [Institute of Physics, Academia Sinica, Taipei 11529, Taiwan (China); Department of Physics, Banaras Hindu University, Varanasi 221005 (India); Wong, Henry T. [Institute of Physics, Academia Sinica, Taipei 11529, Taiwan (China); Wu, Chih-Liang; Wu, Chih-Pan [Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China)
2014-04-04
An ab initio calculation of atomic ionization of germanium by neutrinos was carried out in the framework of multiconfiguration relativistic random phase approximation and benchmarked by related atomic structure and photoabsorption data. This improves over the conventional approach based on scattering off free electrons whose validity at sub-keV energy transfer is questionable. Limits on neutrino magnetic moments are derived using reactor neutrino data taken with low threshold germanium detectors. Future applications of these atomic techniques will greatly reduce the atomic uncertainties in low-energy neutrino and dark matter detections.
Curchod, Basile F. E.; Rauer, Clemens; Marquetand, Philipp; González, Leticia; Martínez, Todd J.
2016-03-01
Full multiple spawning is a formally exact method to describe the excited-state dynamics of molecular systems beyond the Born-Oppenheimer approximation. However, it has been limited until now to the description of radiationless transitions taking place between electronic states with the same spin multiplicity. This Communication presents a generalization of the full and ab initio multiple spawning methods to both internal conversion (mediated by nonadiabatic coupling terms) and intersystem crossing events (triggered by spin-orbit coupling matrix elements) based on a spin-diabatic representation. The results of two numerical applications, a model system and the deactivation of thioformaldehyde, validate the presented formalism and its implementation.
Ab initio study of the EFG at the N sites in imidazole
Energy Technology Data Exchange (ETDEWEB)
Brown Goncalves, Marcos, E-mail: browngon@if.usp.br [Universidade de Sao Paulo, Instituto de Fisica (Brazil); Di Felice, R. [National Center on Nanostructures and Biosystems at Surfaces (S3) of INFM-CNR (Italy); Poleshchuk, O. Kh. [Tomsk State Pedagogical University (Russian Federation); Petrilli, H. M. [Universidade de Sao Paulo, Instituto de Fisica (Brazil)
2008-01-15
We study the nuclear quadrupole interaction at the nitrogen sites in the molecular and crystalline phases of the imidazole compound. We use PAW which is a state-of-the-art method to calculate the electronic structure and electric field gradient at the nucleus in the framework of the density functional theory. The quadrupole frequencies at both imino and amino N sites are in excellent agreement with measurements. This is the first time that the electric field gradient at crystalline imidazole is correctly treated by an ab initio theoretical approach.
Ab initio studies on the mechanic and magnetic properties of PdHx
Institute of Scientific and Technical Information of China (English)
Cui Xin; Liang Xi-Xia; Wang Jian-Tao; Zhao Guo-Zhong
2011-01-01
Based on ab initio total energy calculations, the structural, electronic, mechanic, and magnetic properties of PdHx are investigated. It is found that bulk modulus of PdHx is larger than the metal Pd with the hydrogen storage except Pd4H2. The calculated results for the magnetic moments show that the hydrogen addition weakens the magnetic properties of the PdHx systems. A strong magneto-volume effect is found in PdHx structures as well as Pd. The transition from paramagnetism to ferromagnetism is discussed. The corresponding densities of states for both structures are also shown to understand the magnetic behaviour.
Ab initio Path Integral Molecular Dynamics Based on Fragment Molecular Orbital Method
Fujita, Takatoshi; Watanabe, Hirofumi; Tanaka, Shigenori
2009-10-01
We have developed an ab initio path integral molecular dynamics method based on the fragment molecular orbital method. This “FMO-PIMD” method can treat both nuclei and electrons quantum mechanically, and is useful to simulate large hydrogen-bonded systems with high accuracy. After a benchmark calculation for water monomer, water trimer and glycine pentamer have been studied using the FMO-PIMD method to investigate nuclear quantum effects on structure and molecular interactions. The applicability of the present approach is demonstrated through a number of test calculations.
Monte Carlo methods in AB initio quantum chemistry quantum Monte Carlo for molecules
Lester, William A; Reynolds, PJ
1994-01-01
This book presents the basic theory and application of the Monte Carlo method to the electronic structure of atoms and molecules. It assumes no previous knowledge of the subject, only a knowledge of molecular quantum mechanics at the first-year graduate level. A working knowledge of traditional ab initio quantum chemistry is helpful, but not essential.Some distinguishing features of this book are: Clear exposition of the basic theory at a level to facilitate independent study. Discussion of the various versions of the theory: diffusion Monte Carlo, Green's function Monte Carlo, and release n
Ab-initio density functional theory study of a WO3 NH3-sensing mechanism
Institute of Scientific and Technical Information of China (English)
Hu Ming; Zhang Jie; Wang Wei-Dan; Qin Yu-Xiang
2011-01-01
WO3 bulk and various surfaces are studied by an ab-initio density functional theory technique.The band structures and electronic density states of WO3 bulk are investigated.The surface energies of different WO3 surfaces are compared and then the(002)surface with minimum energy is computed for its NH3 sensing mechanism which explains the results in the experiments.Three adsorption sites are considered.According to the comparisons of the energy and the charge change between before and after adsorption in the optimal adsorption site O1c,the NH3 sensing mechanism is obtained.
Ab initio molecular simulations on specific interactions between amyloid beta and monosaccharides
Nomura, Kazuya; Okamoto, Akisumi; Yano, Atsushi; Higai, Shin'ichi; Kondo, Takashi; Kamba, Seiji; Kurita, Noriyuki
2012-09-01
Aggregation of amyloid β (Aβ) peptides, which is a key pathogenetic event in Alzheimer's disease, can be caused by cell-surface saccharides. We here investigated stable structures of the solvated complexes of Aβ with some types of monosaccharides using molecular simulations based on protein-ligand docking and classical molecular mechanics methods. Moreover, the specific interactions between Aβ and the monosaccharides were elucidated at an electronic level by ab initio fragment molecular orbital calculations. Based on the results, we proposed which type of monosaccharide prefers to have large binding affinity to Aβ and inhibit the Aβ aggregation.
Ab initio adiabatic and quasidiabatic potential energy surfaces of H++ CN system
Indian Academy of Sciences (India)
Bhargava Anusuri; Sanjay Kumar
2016-02-01
We present restricted geometry (collinear and perpendicular approaches of proton) ab initio three dimensional potential energy surfaces for H++ CN system. The calculations were performed at the internally contracted multi-reference configuration interaction level of theory using Dunning’s correlation consistent polarized valence triple zeta basis set. Adiabatic and quasidiabatic surfaces have been computed for the ground and the first excited electronic states. Nonadiabatic effects arising from radial coupling have been analyzed in terms of nonadiabatic coupling matrix elements and coupling potentials.
Wang, Shidong; Wang, Zhao; Setyawan, Wahyu; Mingo, Natalio; Curtarolo, Stefano
2011-10-01
Several thousand compounds from the Inorganic Crystal Structure Database have been considered as nanograined, sintered-powder thermoelectrics with the high-throughput ab-initio AFLOW framework. Regression analysis unveils that the power factor is positively correlated with both the electronic band gap and the carrier effective mass, and that the probability of having large thermoelectric power factors increases with the increasing number of atoms per primitive cell. Avenues for further investigation are revealed by this work. These avenues include the role of experimental and theoretical databases in the development of novel materials.
Sumner, Isaiah; Iyengar, Srinivasan S
2007-10-18
We have introduced a computational methodology to study vibrational spectroscopy in clusters inclusive of critical nuclear quantum effects. This approach is based on the recently developed quantum wavepacket ab initio molecular dynamics method that combines quantum wavepacket dynamics with ab initio molecular dynamics. The computational efficiency of the dynamical procedure is drastically improved (by several orders of magnitude) through the utilization of wavelet-based techniques combined with the previously introduced time-dependent deterministic sampling procedure measure to achieve stable, picosecond length, quantum-classical dynamics of electrons and nuclei in clusters. The dynamical information is employed to construct a novel cumulative flux/velocity correlation function, where the wavepacket flux from the quantized particle is combined with classical nuclear velocities to obtain the vibrational density of states. The approach is demonstrated by computing the vibrational density of states of [Cl-H-Cl]-, inclusive of critical quantum nuclear effects, and our results are in good agreement with experiment. A general hierarchical procedure is also provided, based on electronic structure harmonic frequencies, classical ab initio molecular dynamics, computation of nuclear quantum-mechanical eigenstates, and employing quantum wavepacket ab initio dynamics to understand vibrational spectroscopy in hydrogen-bonded clusters that display large degrees of anharmonicities.
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.
Heats of Segregation of BCC Binaries from ab Initio and Quantum Approximate Calculations
Good, Brian S.
2004-01-01
We compare dilute-limit heats of segregation for selected BCC transition metal binaries computed using ab initio and quantum approximate energy methods. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent LMTO-based parameters. Quantum approximate segregation energies are computed with and without atomistic relaxation, while the ab initio calculations are performed without relaxation. Results are discussed within the context of a segregation model driven by strain and bond-breaking effects. We compare our results with full-potential quantum calculations and with available experimental results.
Emergence of rotational bands in ab initio no-core configuration interaction calculations
Caprio, M A; Vary, J P; Smith, R
2015-01-01
Rotational bands have been observed to emerge in ab initio no-core configuration interaction (NCCI) calculations for p-shell nuclei, as evidenced by rotational patterns for excitation energies, electromagnetic moments, and electromagnetic transitions. We investigate the ab initio emergence of nuclear rotation in the Be isotopes, focusing on 9Be for illustration, and make use of basis extrapolation methods to obtain ab initio predictions of rotational band parameters for comparison with experiment. We find robust signatures for rotational motion, which reproduce both qualitative and quantitative features of the experimentally observed bands.
Energy Technology Data Exchange (ETDEWEB)
Lavrentyev, A.A.; Gabrelian, B.V.; Vorzhev, V.B.; Nikiforov, I.Ya. [Department of Physics, Don State Technical University, Gagarin Sq. 1, Rostov-on-Don (Russian Federation); Khyzhun, O.Yu. [Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, UA-03142 Kyiv (Ukraine)], E-mail: khyzhun@ipms.kiev.ua
2009-03-20
To investigate the influence of substitution of carbon atoms for nitrogen atoms in the cubic TaC{sub x}N{sub 1-x} carbonitrides, total and partial densities of states were calculated for TaC, TaC{sub 0.5}N{sub 0.5} and TaN compounds (NaCl structure) using the self-consistent cluster (with the FEFF8 code) and ab initio band-structure augmented plane wave + local orbitals (APW + LO) methods. In the present work a rather good agreement of the theoretical FEFF8 and APW + LO data for electronic properties of the TaC{sub x}N{sub 1-x} system under consideration was obtained. The results indicate that a strong hybridization of the Ta 5d- and C(N) 2p-like states is characteristic for the valence band of the TaC{sub x}N{sub 1-x} carbonitrides. When going from TaC to TaN through the TaC{sub 0.5}N{sub 0.5} carbonitride, the main maxima of curves representing total and partial Ta 5d densities of states shift in the direction opposite to the position of the Fermi level. In the above sequence of compounds, an increase of occupation of the near-Fermi sub-band formed by contributions of Ta 5d(t{sub 2g}) states has been detected. The theoretical FEFF8 and APW + LO results for the electronic structure of the TaC{sub x}N{sub 1-x} carbonitrides were found to be in excellent agreement with the experimental data derived in the present work employing X-ray photoelectron, emission and absorption spectroscopy methods for cubic TaC{sub 0.98}, TaC{sub 0.52}N{sub 0.49} and TaN{sub 0.97} compounds.
Institute of Scientific and Technical Information of China (English)
郑浩平; 吴丽华; 李根
2013-01-01
用第一性原理、全电子、从头计算方法构造了水溶液对缬氨酸(Val)电子结构的等效势.首先用自由团簇计算法得到能量最低时水分子与缬氨酸的相对空间位形,然后用团簇埋入自洽计算(SCCE)方法计算缬氨酸在水分子势下的电子结构,最后用偶极子势代替水分子势.结果表明:由于水溶液的存在,缬氨酸费米面下八个能级每个能级平均上升了约0.775 5 eV；水溶液对缬氨酸电子结构的影响可以很好地被偶极子势模拟.因此,所得的偶极子势可以直接运用到水溶液中蛋白质电子结构的计算中.%The equivalent potential of water for the electronic structure of valine (Val) was constructed on the basis of the first-principles, all-electron, ab initio calculations. The process involved three steps. First, a search for the minimum-energy configuration of the system Val + 7H2O was carried out by free cluster calculation. Then, the electronic structure of valine with the potential of water molecules was calculated with the self-consistent cluster-embedding (SCCE) method. Finally, the effect of water was simulated on valine by dipoles. Results show that the major effect of water on the electronic structure of valine is to raise the eigenvalues of eight orbitals under Fermi surface by about 0. 775 5 eV on average. The effect of water on the electronic structure of valine can be well simulated by dipoles. The equivalent potential obtained can be applied directly to the calculation of the electronic structures of proteins in solution.
A unified scheme for ab initio molecular orbital theory and path integral molecular dynamics
Shiga, Motoyuki; Tachikawa, Masanori; Miura, Shinichi
2001-11-01
We present a general approach for accurate calculation of chemical substances which treats both nuclei and electrons quantum mechanically, adopting ab initio molecular orbital theory for the electronic structure and path integral molecular dynamics for the nuclei. The present approach enables the evaluation of physical quantities dependent on the nuclear configuration as well as the electronic structure, within the framework of Born-Oppenheimer adiabatic approximation. As an application, we give the path integral formulation of electric response properties—dipole moment and polarizability, which characterize the changes both in electronic structure and nuclear configuration at a given temperature when uniform electrostatic field is present. We also demonstrate the calculation of a water molecule using the present approach and the result of temperature and isotope effects is discussed.
The {\\it ab initio} calculation of spectra of open shell diatomic molecules
Tennyson, Jonathan; McKemmish, Laura K; Yurchenko, Sergei N
2016-01-01
The spectra (rotational, rotation-vibrational or electronic) of diatomic molecules due to transitions involving only closed-shell ($^1\\Sigma$) electronic states follow very regular, simple patterns and their theoretical analysis is usually straightforward. On the other hand, open-shell electronic states lead to more complicated spectral patterns and, moreover, often appear as a manifold of closely lying electronic states, leading to perturbations with even larger complexity. This is especially true when at least one of the atoms is a transition metal. Traditionally these complex cases have been analysed using approaches based on perturbation theory, with semi-empirical parameters determined by fitting to spectral data. Recently the needs of two rather diverse scientific areas have driven the demand for improved theoretical models of open-shell diatomic systems based on an \\emph{ab initio} approach, these areas are ultracold chemistry and the astrophysics of "cool" stars, brown dwarfs and most recently extraso...
Ab initio intermolecular potential energy surface of He-LiH
Institute of Scientific and Technical Information of China (English)
鄢国森; 杨明晖; 谢代前
1997-01-01
The intermolecular potential energy surface of He-LiH complex was studied using the full-electronic complete forth-order Miller-Plesset perturbation (MPPT) method.In ab initio calculations,the bond length of LiH was fixed at 0 159 5 nm.The potential has two local minima of Vm=-179.93 cm for the linear He LiH geormetrv at Rm=0.227 nm and Vm=-10.44 cm-1 for the linear He-HL1 geometry at Rm=0.516 nm The potemal exhibits strong anisotropy The analytic potential function with 31 parameters was determined by fitting to the calculated ab,mtio potentials The influence of variation of LiH bond length on the potential energy surface was also studied
Directory of Open Access Journals (Sweden)
S. J Hashemifar
2015-01-01
Full Text Available In this paper, the structural, magnetic, and electronic properties of two- to nine-atom copper and silver clusters and their alloys with one palladium atom are investigated by using full-potential all-electron density functional computations. After calculating minimized energy of several structural isomers of every nanocluster, it is argued that the small size nanoclusters (up to size of 6, prefer planar structures, while by increasing size a 2D-3D structural transformation is observed. The structural transformation of pure and copper-palladium clusters occurs in the size of seven and that of silver-palladium cluster in happens at the size of six. The calculated second difference and dissociation energies confirm that the two- and eight- atom pure clusters and three- and seven- atom alloyed clusters are magic clusters. The electronic and magnetic properties of stable isomers are calculated and considered after applying many body based GW correction.
Ab-initio study of magnetic properties and phase transitions in Ga (Mn) N with Monte Carlo approach
Energy Technology Data Exchange (ETDEWEB)
Sbai, Y.; Ait Raiss, A.; Salmani, E. [LMPHE (URAC 12), Faculty of Science, Mohammed V University, Av. Ibn Batouta, Rabat (Morocco); Bahmad, L., E-mail: Bahmad@fsr.ac.ma [LMPHE (URAC 12), Faculty of Science, Mohammed V University, Av. Ibn Batouta, Rabat (Morocco); Benyoussef, A. [LMPHE (URAC 12), Faculty of Science, Mohammed V University, Av. Ibn Batouta, Rabat (Morocco); Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco)
2015-12-15
On the basis of ab-initio calculations and Monte Carlo simulations the magnetic and electronic properties of Gallium nitride (GaN) doped with the transition metal Manganese (Mn) were studied. The ab initio calculations were done using the AKAI–KKR–CPA method within the Local Density Approximation (LDA) approximation. We doped our Diluted Magnetic Semiconductor (DMS), with different concentrations of magnetic impurities Mn and plotted the density of state (DOS) for each one. Showing a half-metallic behavior and ferromagnetic state especially for Ga{sub 0.95}Mn{sub 0.05}N making this DMS a strong candidate for spintronic applications. Moreover, the magnetization and susceptibility of our system as a function of the temperature has been calculated and give for various system size L to study the size effect. In addition, the transition temperature was deduced from the peak of the susceptibility. The Ab initio results are in good agreement with literature especially for (x=0.05) of Mn which gives the most interesting results. - Highlights: • The AKAI–KKR–CPA method has been applied to study the doped compound GaN:Mn. • The local density approximation (LDA) has been applied. • The ab-initio calculations have been performed. • The density of states (DOS) have been plotted for differents doping concentrations, using Monte Carlo simulations.
Marsalek, Ondrej; Markland, Thomas E
2016-02-07
Path integral molecular dynamics simulations, combined with an ab initio evaluation of interactions using electronic structure theory, incorporate the quantum mechanical nature of both the electrons and nuclei, which are essential to accurately describe systems containing light nuclei. However, path integral simulations have traditionally required a computational cost around two orders of magnitude greater than treating the nuclei classically, making them prohibitively costly for most applications. Here we show that the cost of path integral simulations can be dramatically reduced by extending our ring polymer contraction approach to ab initio molecular dynamics simulations. By using density functional tight binding as a reference system, we show that our ring polymer contraction scheme gives rapid and systematic convergence to the full path integral density functional theory result. We demonstrate the efficiency of this approach in ab initio simulations of liquid water and the reactive protonated and deprotonated water dimer systems. We find that the vast majority of the nuclear quantum effects are accurately captured using contraction to just the ring polymer centroid, which requires the same number of density functional theory calculations as a classical simulation. Combined with a multiple time step scheme using the same reference system, which allows the time step to be increased, this approach is as fast as a typical classical ab initio molecular dynamics simulation and 35× faster than a full path integral calculation, while still exactly including the quantum sampling of nuclei. This development thus offers a route to routinely include nuclear quantum effects in ab initio molecular dynamics simulations at negligible computational cost.
Energy Technology Data Exchange (ETDEWEB)
Allali, D. [Laboratory for Developing New Materials and their Characterization, University of Setif 1, 19000 Setif (Algeria); Bouhemadou, A., E-mail: a_bouhemadou@yahoo.fr [Laboratory for Developing New Materials and their Characterization, University of Setif 1, 19000 Setif (Algeria); Safi, E. Muhammad Abud Al [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Bin-Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Department of Physics, Faculty of Science and Humanitarian Studies, Salman Bin Abdalaziz University, Alkharj 11942 (Saudi Arabia); Chegaar, M. [Department of Physics, Faculty of Science, University of Setif 1, 19000 Setif (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, 29000 Mascara (Algeria); Reshak, A.H. [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilson (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia)
2014-06-15
We report ab initio density functional theory calculations of the structural, electronic and optical properties of the spinel oxides SiMg{sub 2}O{sub 4}, SiZng{sub 2}O{sub 4}, and SiCd{sub 2}O{sub 4} using the full-potential linearized augmented plane-wave method. The structural parameters calculated using both the local density and generalized gradient approximations to the exchange-correlation potential are consistent with the literature data. To calculate the electronic properties, the exchange-correlation potential is treated with various functionals, and we find that the newly developed Tran–Blaha-modified Becke–Johnson functional significantly improves the band gap. We predict a direct band gap in all of the considered SiB{sub 2}O{sub 4} compounds, and the band gaps continuously decrease as the atomic size of the B element increases. The decrease in the fundamental direct band gap (Γ–Γ) from SiMg{sub 2}O{sub 4} to SiZn{sub 2}O{sub 4} to SiCd{sub 2}O{sub 4} can be attributed to p–d mixing in the upper valence bands of SiZn{sub 2}O{sub 4} and SiCd{sub 2}O{sub 4}. The lowest conduction band is well dispersive, similar to that found for transparent conducting oxides such as ZnO. This band is mainly defined by the s and p electrons of the Si and B (B=Mg, Zn, Cd) atoms. The topmost valence band is considerably less dispersive and is defined by O-2p and B–d electrons. The charge-carrier effective masses are evaluated at the topmost valence band and at the bottommost conduction band that were calculated. The frequency-dependent complex dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity and electron energy loss function were estimated. We find that the value of the zero-frequency limit of the dielectric function ε(0) increases as the band gap decreases. The origins of the peaks and structures in the optical spectra are determined in terms of the calculated energy band structures.
Energy Technology Data Exchange (ETDEWEB)
Guemou, M., E-mail: guemoumhamed7@gmail.com [Engineering Physics Laboratory, Ibn Khaldoun University of Tiaret, Postbox 78-Zaaroura, 14000 Tiaret (Algeria); Abdiche, A.; Riane, R. [Applied Materials Laboratory, Research Center, University of Sidi Bel Abbes, 22000 Sidi Bel Abbes (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, 29000 Mascara (Algeria)
2014-03-01
In this work, we present a density-functional theory study of structural, electronic and optical properties of BAs, BN binary compounds and their ternary BN{sub x}As{sub 1−x} solid solutions. The calculations are done by using the all-electron full potential linear augmented plane-wave method (FP-LAPW) as employed in WIEN2k code. For the exchange-correlation potential, local-density approximation (LDA) and generalized gradient approximation (GGA) have been used to calculate theoretical lattice parameters, bulk modulus, and its pressure derivative. The electronic band structure of these compounds have been calculated by using the above two approximations. We have also investigated in this article the density of state and the optical properties such as the dielectric function and the refractive index of BAs, BN and BN{sub 0.25}As{sub 0.75} compounds by using the above method. The results obtained for structural and electronic properties are compared with experimental data and other computational work. It has been found that the energy bands with all these approximations are similar except the band gap values. It has also been found that our results with LDA and GGA are in good agreement with other computational work wherever these are available.
Teeninga, Hermannus
1983-01-01
This thesis describes an investigation of the electronic structure of sulfonamidyl radicals (R1SO2NR2) and some structurally related carboxamidyl radicals (R1C(0)NR2). Both types of radicals have been invoked as intermediates in several chemical reactions. The present work originates from our intere
DEFF Research Database (Denmark)
Wolf, T. J. A.; Kuhlman, Thomas Scheby; Schalk, O.
2014-01-01
Time-resolved photoelectron spectroscopy and ab initio multiple spawning were applied to the ultrafast non-adiabatic dynamics of hexamethylcyclopentadiene. The high level of agreement between experiment and theory associates wavepacket motion with a distinct degree of freedom....
Renison, C Alicia; Fernandes, Kyle D; Naidoo, Kevin J
2015-07-05
This article describes an extension of the quantum supercharger library (QSL) to perform quantum mechanical (QM) gradient and optimization calculations as well as hybrid QM and molecular mechanical (QM/MM) molecular dynamics simulations. The integral derivatives are, after the two-electron integrals, the most computationally expensive part of the aforementioned calculations/simulations. Algorithms are presented for accelerating the one- and two-electron integral derivatives on a graphical processing unit (GPU). It is shown that a Hartree-Fock ab initio gradient calculation is up to 9.3X faster on a single GPU compared with a single central processing unit running an optimized serial version of GAMESS-UK, which uses the efficient Schlegel method for s- and l-orbitals. Benchmark QM and QM/MM molecular dynamics simulations are performed on cellobiose in vacuo and in a 39 Å water sphere (45 QM atoms and 24843 point charges, respectively) using the 6-31G basis set. The QSL can perform 9.7 ps/day of ab initio QM dynamics and 6.4 ps/day of QM/MM dynamics on a single GPU in full double precision. © 2015 Wiley Periodicals, Inc.
Ab initio calculations of the optical properties of crystalline and liquid InSb
Energy Technology Data Exchange (ETDEWEB)
Sano, Haruyuki, E-mail: h-sano@ishikawa-nct.ac.jp [National Institute of Technology, Ishikawa College, Kitacyujo, Tsubata, Ishikawa 929-0392 (Japan); Mizutani, Goro [School of Materials Science, Japan Advanced Institute of Science and Technology, Tatsunokuchi, Ishikawa 923-1292 (Japan)
2015-11-15
Ab initio calculations of the electronic and optical properties of InSb were performed for both the crystalline and liquid states. Two sets of atomic structure models for liquid InSb at 900 K were obtained by ab initio molecular dynamics simulations. To reduce the effect of structural peculiarities in the liquid models, an averaging of the two sets of the calculated electronic and optical properties corresponding to the two liquid models was performed. The calculated results indicate that, owing to the phase transition from crystal to liquid, the density of states around the Fermi level increases. As a result, the energy band gap opening near the Fermi level disappears. Consequently, the optical properties change from semiconductor to metallic behavior. Namely, owing to the melting of InSb, the interband transition peaks disappear and a Drude-like dispersion is observed in the optical dielectric functions. The optical absorption at a photon energy of 3.06 eV, which is used in Blu-ray Disc systems, increases owing to the melting of InSb. This increase in optical absorption is proposed to result from the increased optical transitions below 2 eV.
Tanha, Matteus; Cappiello, Alex; Gordon, Geoffrey J; Yaron, David J
2013-01-01
A means to take advantage of molecular similarity to lower the computational cost of electronic structure theory is proposed, in which parameters are embedded into a low-cost, low-level (LL) ab initio theory and adjusted to obtain agreement with a higher level (HL) ab initio theory. This approach is explored by training such a model on data for ethane and testing the resulting model on methane, propane and butane. The electronic distribution of the molecules is varied by placing them in strong electrostatic environments consisting of random charges placed on the corners of a cube. The results find that parameters embedded in HF/STO-3G theory can be adjusted to obtain agreement, to within about 2 kcal/mol, with results of HF/6-31G theory. Obtaining this level of agreement requires the use of parameters that are functions of the bond lengths, atomic charges, and bond orders within the molecules. The argument is made that this approach provides a well-controlled means to take advantage of molecular similarity in...
Ab initio evaluations of the He solubility in liquid Li
Energy Technology Data Exchange (ETDEWEB)
Sedano, Luis A. [EURATOM-CIEMAT Assoc., Materials for Fusion Program, Bd. 43 P0.04, Avda. Complutense 22, 28040 Madrid (Spain)]. E-mail: luis.sedano@ciemat.es; Hassanein, Ahmed [Argonne Nat. Lab, 9700 South Class Av., Argonne, IL (United States)]. E-mail: hassanein@anl.gov; Sanz, Javier [ETSII-UNED, c/Juan del Rosal, 12, 28040 Madrid (E) (Spain)]. E-mail: jsanz@ind.UNED.es
2005-11-15
Modified embedding atom methods (MEAM) are developed to have predictions of the partial molar heat of solution (-H{sub s}) by direct simulation of metal cohesion, He-metal and He-He interaction. Transitions from crystalline Li to configurations, having the liquid Li structure's factors (h-bar (q)), are simulated ab initio. Once h-bar (q) reproduced, He atoms are added, one by one, to the Li system. Parallel lines for each case, with slopes clearly independent on the number of He atoms in the system, are obtained for energy versus pressure at given temperatures. Average differences between two adjacent parallels at zero pressure, once kinetic energy of the system discounted, represents the energy gained by an He atom when added to the Li system, related to the solution energy -H{sub s}. The molar excess entropy of gas in solution (S-bar {sub l}{sup ex}) is previously evaluated following diverse fundamental approaches: a 'thermodynamic liquid-hole' (TL-H) model for alkali liquids and a statistical-mechanics (Neff and McQuarrie's) model (SMM). Between 600 and 900 deg. C, a typical range of interest for the use of Li in fusion technology, the computed values for the (He) Henry's constant in Li range from 8x10{sup -14} to 10{sup -13} at. fr. Pa{sup -1}.
Ab initio calculation of the potential bubble nucleus $^{34}$Si
Duguet, T; Lecluse, S; Barbieri, C; Navrátil, P
2016-01-01
The possibility that an unconventional depletion in the center of the charge density distribution of certain nuclei occurs due to a purely quantum mechanical effect has attracted theoretical and experimental attention in recent years. We report on ab initio self-consistent Green's function calculations of one of such candidates, $^{34}$Si, together with its Z+2 neighbour $^{36}$S. Binding energies, rms radii and density distributions of the two nuclei as well as low-lying spectroscopy of $^{35}$Si, $^{37}$S, $^{33}$Al and $^{35}$P are discussed. The interpretation of one-nucleon removal and addition spectra in terms of the evolution of the underlying shell structure is also provided. The study is repeated using several chiral effective field theory Hamiltonians as a way to test the robustness of the results with respect to input inter-nucleon interactions. The prediction regarding the (non-)existence of the bubble structure in $^{34}$Si varies significantly with the nuclear Hamiltonian used. However, demandin...
Exploring the free energy surface using ab initio molecular dynamics
Samanta, Amit; Morales, Miguel A.; Schwegler, Eric
2016-04-01
Efficient exploration of configuration space and identification of metastable structures in condensed phase systems are challenging from both computational and algorithmic perspectives. In this regard, schemes that utilize a set of pre-defined order parameters to sample the relevant parts of the configuration space [L. Maragliano and E. Vanden-Eijnden, Chem. Phys. Lett. 426, 168 (2006); J. B. Abrams and M. E. Tuckerman, J. Phys. Chem. B 112, 15742 (2008)] have proved useful. Here, we demonstrate how these order-parameter aided temperature accelerated sampling schemes can be used within the Born-Oppenheimer and the Car-Parrinello frameworks of ab initio molecular dynamics to efficiently and systematically explore free energy surfaces, and search for metastable states and reaction pathways. We have used these methods to identify the metastable structures and reaction pathways in SiO2 and Ti. In addition, we have used the string method [W. E, W. Ren, and E. Vanden-Eijnden, Phys. Rev. B 66, 052301 (2002); L. Maragliano et al., J. Chem. Phys. 125, 024106 (2006)] within the density functional theory to study the melting pathways in the high pressure cotunnite phase of SiO2 and the hexagonal closed packed to face centered cubic phase transition in Ti.
Ab initio predictions of the symmetry energy and recent constraints
Sammarruca, Francesca
2017-01-01
The symmetry energy plays a crucial role in the structure and the dynamics of neutron-rich systems, including the formation of neutron skins, the location of neutron drip lines, as well as intriguing correlations with the structure of compact stars. With experimental efforts in progress or being planned to shed light on the less known aspects of the nuclear chart, microscopic predictions based on ab initio approaches are very important. In recent years, chiral effective field theory has become popular because of its firm connection with quantum chromodynamics and its systematic approach to the development of nuclear forces. Predictions of the symmetry energy obtained from modern chiral interactions will be discussed in the light of recent empirical constraints extracted from heavy ion collisions at 400 MeV per nucleon at GSI. Applications of our equations of state to neutron-rich systems will also be discussed, with particular emphasis on neutron skins, which are sensitive to the density dependence of the symmetry energy.
Ab initio no-core solutions for $^6$Li
Shin, Ik Jae; Maris, Pieter; Vary, James P; Forssén, Christian; Rotureau, Jimmy; Michel, Nicolas
2016-01-01
We solve for properties of $^6$Li in the ab initio No-Core Full Configuration approach and we separately solve for its ground state and $J^{\\pi}=2_{2}^{+}$ resonance with the Gamow Shell Model in the Berggren basis. We employ both the JISP16 and chiral NNLO$_{opt}$ realistic nucleon-nucleon interactions and investigate the ground state energy, excitation energies, point proton root-mean-square radius and a suite of electroweak observables. We also extend and test methods to extrapolate the ground state energy, point proton root-mean-square radius, and electric quadrupole moment. We attain improved estimates of these observables in the No-Core Full Configuration approach by using basis spaces up through N$_{max}$=18 that enable more definitive comparisons with experiment. Using the Density Matrix Renormalization Group approach with the JISP16 interaction, we find that we can significantly improve the convergence of the Gamow Shell Model treatment of the $^6$Li ground state and $J^{\\pi}=2_{2}^{+}$ resonance by ...
An efficient approach to ab initio Monte Carlo simulation.
Leiding, Jeff; Coe, Joshua D
2014-01-21
We present a Nested Markov chain Monte Carlo (NMC) scheme for building equilibrium averages based on accurate potentials such as density functional theory. Metropolis sampling of a reference system, defined by an inexpensive but approximate potential, was used to substantially decorrelate configurations at which the potential of interest was evaluated, thereby dramatically reducing the number needed to build ensemble averages at a given level of precision. The efficiency of this procedure was maximized on-the-fly through variation of the reference system thermodynamic state (characterized here by its inverse temperature β(0)), which was otherwise unconstrained. Local density approximation results are presented for shocked states of argon at pressures from 4 to 60 GPa, where-depending on the quality of the reference system potential-acceptance probabilities were enhanced by factors of 1.2-28 relative to unoptimized NMC. The optimization procedure compensated strongly for reference potential shortcomings, as evidenced by significantly higher speedups when using a reference potential of lower quality. The efficiency of optimized NMC is shown to be competitive with that of standard ab initio molecular dynamics in the canonical ensemble.
Engineering Room-temperature Superconductors Via ab-initio Calculations
Gulian, Mamikon; Melkonyan, Gurgen; Gulian, Armen
The BCS, or bosonic model of superconductivity, as Little and Ginzburg have first argued, can bring in superconductivity at room temperatures in the case of high-enough frequency of bosonic mode. It was further elucidated by Kirzhnitset al., that the condition for existence of high-temperature superconductivity is closely related to negative values of the real part of the dielectric function at finite values of the reciprocal lattice vectors. In view of these findings, the task is to calculate the dielectric function for real materials. Then the poles of this function will indicate the existence of bosonic excitations which can serve as a "glue" for Cooper pairing, and if the frequency is high enough, and the dielectric matrix is simultaneously negative, this material is a good candidate for very high-Tc superconductivity. Thus, our approach is to elaborate a methodology of ab-initio calculation of the dielectric function of various materials, and then point out appropriate candidates. We used the powerful codes (TDDF with the DP package in conjunction with ABINIT) for computing dielectric responses at finite values of the wave vectors in the reciprocal lattice space. Though our report is concerned with the particular problem of superconductivity, the application range of the data processing methodology is much wider. The ability to compute the dielectric function of existing and still non-existing (though being predicted!) materials will have many more repercussions not only in fundamental sciences but also in technology and industry.
The Hydration Structure of Carbon Monoxide by Ab Initio Methods
Awoonor-Williams, Ernest
2016-01-01
The solvation of carbon monoxide (CO) in liquid water is important for understanding its toxicological effects and biochemical roles. In this paper, we use ab initio molecular dynamics (AIMD) and CCSD(T)-F12 calculations to assess the accuracy of the Straub and Karplus molecular mechanical (MM) model for CO(aq). The CCSD(T)-F12 CO--H2O potential energy surfaces show that the most stable structure corresponds to water donating a hydrogen bond to the C center. The MM-calculated surface it incorrectly predicts that the O atom is a stronger hydrogen bond acceptor than the C atom. The AIMD simulations indicate that CO is solvated like a hydrophobic solute, with very limited hydrogen bonding with water. The MM model tends to overestimate the degree of hydrogen bonding and overestimates the atomic radius of the C atom. The calculated Gibbs energy of hydration is in good agreement with experiment (9.3 kJ/mol calc. vs 10.7 kJ/mol exptl.). The calculated diffusivity of CO(aq) in TIP3P-model water was 5.19 x 10-5 cm2/s ...
Ab initio transport across bismuth selenide surface barriers
Narayan, Awadhesh
2014-11-24
© 2014 American Physical Society. We investigate the effect of potential barriers in the form of step edges on the scattering properties of Bi2Se3(111) topological surface states by means of large-scale ab initio transport simulations. Our results demonstrate the suppression of perfect backscattering, while all other scattering processes, which do not entail a complete spin and momentum reversal, are allowed. Furthermore, we find that the spin of the surface state develops an out-of-plane component as it traverses the barrier. Our calculations reveal the existence of quasibound states in the vicinity of the surface barriers, which appear in the form of an enhanced density of states in the energy window corresponding to the topological state. For double barriers we demonstrate the formation of quantum well states. To complement our first-principles results we construct a two-dimensional low-energy effective model and illustrate its shortcomings. Our findings are discussed in the context of a number of recent experimental works.
Arghavani Nia, Borhan; Sedighi, Matin; Shahrokhi, Masoud; Moradian, Rostam
2013-11-01
A density functional theory study of structural, electronical and optical properties of Ca3Sb2 compound in hexagonal and cubic phases is presented. In the exchange-correlation potential, generalized gradient approximation (PBE-GGA) has been used to calculate lattice parameters, bulk modulus, cohesive energy, dielectric function and energy loss spectra. The electronic band structure of this compound has been calculated using the above two approximations as well as another form of PBE-GGA, proposed by Engle and Vosko (EV-GGA). It is found that the hexagonal phase of Ca3Sb2 has an indirect gap in the Γ→N direction; while in the cubic phase there is a direct-gap at the Γ point in the PBE-GGA and EV-GGA. Effects of applying pressure on the band structure of the system studied and optical properties of these systems were calculated.
Energy Technology Data Exchange (ETDEWEB)
Al-Douri, Y.; Ahmad, S.; Hashim, U. [Institute of Nano Electronic Engineering, University Malaysia Perlis, Kangar, Perlis (Malaysia); Reshak, Ali Hussain [Institute of Nano Electronic Engineering, University Malaysia Perlis, Kangar, Perlis (Malaysia); Institute of Physical Biology, South Bohemia University, Nove Hrady (Czech Republic); Baaziz, H.; Charifi, Z. [Physics Department, Faculty of Science and Engineering, University of M' sila (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modelisation Mathematique (LPQ3M), Universite de Mascara (Algeria); Department of Physics and Astronomy, Faculty of Science, King Saud University, Riyadh (Saudi Arabia)
2010-12-15
The structural, electronic and optical properties of cubic CdS{sub 1-x}Te{sub x} alloys, with Te-concentrations varying from 0% up to 100% are investigated. The calculations are based on the total-energy calculations using the full potential-linearized augmented plane wave (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA) for the total-energy calculations, while for electronic properties in addition to that the Engel-Vosko (EV-GGA) formalism was also applied. The ground state properties for all Te-concentrations are presented. The optical dielectric constant is also determined for both the binary and their related ternary alloys. (author)
Balan, Etienne; Lazzeri, M.; Mauri, F.; Calas, G.
2007-01-01
We review here some recent applications of ab initio calculations to the modelling of spectroscopic and energetic properties of minerals, which are key components of lateritic soils or govern their geochemical properties. Quantum mechanical ab initio calculations are based on density functional theory and density functional perturbation theory. Among the minerals investigated, zircon is a typical resistant primary mineral. Its resistance to weathering is at the origin of the peculiar geochemi...
2015-06-28
ghanshyam.vaghjiani@us.af.mil Ab initio Quantum Chemical Reaction Kinetics: Recent Applications in Combustion Chemistry Ghanshyam L. Vaghjiani* DISTRIBUTION A...Charts 3. DATES COVERED (From - To) June 2015-June 2015 4. TITLE AND SUBTITLE AB INITIO QUANTUM CHEMICAL REACTION KINETICS: RECENT APPLICATIONS IN...COMBUSTION CHEMISTRY (Briefing Charts) 5a. CONTRACT NUMBER In-House 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Ghanshyam L
An ab initio Non-Equilibrium Green Function Approach to Charge Transport: Dithiolethine
Institute of Scientific and Technical Information of China (English)
Alexander Schnurpfeil; SONG Bo; Martin Albrecht
2006-01-01
@@ We present a novel ab initio non-equilibrium approach to calculate the current across a molecular junction. The method rests on a wavefunction-based full ab initio description of the central region of the junction combined with a tight binding approximation for the electrodes in the frame of the Keldysh Green function formalism. Our procedure is demonstrated for a dithiolethine molecule located between silver electrodes. The main conducting channel is identified and the full current-voltage characteristic is calculated.
Energy Technology Data Exchange (ETDEWEB)
Arghavani Nia, Borhan, E-mail: b.arghavani@gmail.com [Department of Physics, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Sedighi, Matin [Department of Physics, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Shahrokhi, Masoud [Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Moradian, Rostam [Nano-Science and Nano-Technology Research Center, Razi University, Kermanshah (Iran, Islamic Republic of); Computational Physics Science Research Laboratory, Department of Nano-Science, Institute for Studies in Theoretical Physics and Mathematics (IPM), P.O. Box 19395-1795, Tehran (Iran, Islamic Republic of)
2013-11-15
A density functional theory study of structural, electronical and optical properties of Ca{sub 3}Sb{sub 2} compound in hexagonal and cubic phases is presented. In the exchange–correlation potential, generalized gradient approximation (PBE-GGA) has been used to calculate lattice parameters, bulk modulus, cohesive energy, dielectric function and energy loss spectra. The electronic band structure of this compound has been calculated using the above two approximations as well as another form of PBE-GGA, proposed by Engle and Vosko (EV-GGA). It is found that the hexagonal phase of Ca{sub 3}Sb{sub 2} has an indirect gap in the Γ→N direction; while in the cubic phase there is a direct-gap at the Γ point in the PBE-GGA and EV-GGA. Effects of applying pressure on the band structure of the system studied and optical properties of these systems were calculated. - Graphical abstract: A density functional theory study of structural, electronic and optical properties of Ca{sub 3}Sb{sub 2} compound in hexagonal and cubic phases is presented. Display Omitted - Highlights: • Physical properties of Ca{sub 3}Sb{sub 2} in hexagonal and cubic phases are investigated. • It is found that the hexagonal phase is an indirect gap semiconductor. • Ca{sub 3}Sb{sub 2} is a direct-gap semiconductor at the Γ point in the cubic phase. • By increasing pressure the semiconducting band gap and anti-symmetry gap are decreased.
Energy Technology Data Exchange (ETDEWEB)
Kumar, Santosh, E-mail: skjiitr@gmail.com [Department of Materials Science and Engineering, University of Seoul, 90 JunNong-dong, DongDaeMun-gu, Seoul-130743 (Korea, Republic of); Jung, JaePil, E-mail: jpjung@uos.ac.kr [Department of Materials Science and Engineering, University of Seoul, 90 JunNong-dong, DongDaeMun-gu, Seoul-130743 (Korea, Republic of)
2013-01-01
Highlights: Black-Right-Pointing-Pointer Structural, mechanical and electronic properties of Ag{sub 3}Sn determined. Black-Right-Pointing-Pointer Elastic anisotropy of Ag{sub 3}Sn is discussed comprehensively. Black-Right-Pointing-Pointer Scatter in the experimentally obtained elastic modulus values is explained. Black-Right-Pointing-Pointer Electronic properties discussed using overlap population, band structure and DOS. Black-Right-Pointing-Pointer Debye temperature of Ag{sub 3}Sn is estimated to be 251 K. - Abstract: First principle calculations based on density functional theory (DFT) are used to calculate the structural, elastic and electronic properties of tin-silver intermetallic compound (Ag{sub 3}Sn), found mainly in lead free solder joints. In present work, for the exchange-correlation energy, generalized gradient approximation (GGA) functional is used. The calculated lattice constants are found to be within 2% error of the experimental values. All single crystal elastic constants are computed from which values of shear modulus, bulk modulus, Young's modulus and Poisson's ratio for polycrystalline Ag{sub 3}Sn are calculated using Voigt and Hill approximations. To explain the scatter in the experimentally determined values of elastic constants, directional dependence of bulk modulus and Young's modulus are estimated. The values of Young's modulus calculated along different planes are found to be in same range as experimentally determined values. Various anisotropic indices like universal anisotropic index, Zener anisotropic index, shear anisotropic index and others are calculated to study elastic anisotropy. Further anisotropy in Poisson's ratio is studied by calculating their values along six lower-index planes. The value of Debye temperature calculated using elastic data of present work is found be to higher than the values obtained using resistivity measurement, which can be attributed to temperature dependence. Electronic
Sivaranjani, T.; Periandy, S.; Xavier, S.
2016-03-01
The FT-IR and FT-Raman spectra of 3-pyridinemethanol (3PYRM) have been recorded in the regions 4000-400 and 4000-100 cm-1 respectively. The vibrational analysis of 3PYRM was carried out using wavenumbers computed by HF and DFT (B3LYP) methods with 6-311++G (d, p) basis set, along with experimental values. The conformational analyses were performed and the energies of the different possible conformers were determined. The total electron density and MESP surfaces of the molecules were constructed using B3LYP/6-311++G (d, p) method to display nucleophilic and electrophilic region globally. The HOMO and LUMO energies were measured and different reactivity descriptors are discussed the active sites of the molecule. Natural Bond Orbital Analysis is discussed and possible transition are correlated with the electronic transitions. Milliken's net charges and the atomic natural charges are also predicted. The 13C and 1H NMR chemical shifts were computed at the B3LYP/6-311++G (2d, p) level by applying GIAO theory and compared with the experimental spectra recorded using the high resolution of 100 MHz and 400 MHz NMR spectrometer with electromagnetic field strength 9.1T, respectively. The temperature dependence of the thermodynamic properties; heat capacity, entropy and enthalpy for the title compounds were also determined by B3LYP/6-311++G (d, p) method.
Seda, Josef; Burda, Jaroslav V; Leszczynski, Jerzy
2005-02-01
SAC (symmetry adapted cluster)/SAC-CI and CASPT2 (multiconfigurational second-order perturbation theory) electron excitation spectra of free-base porphin and magnesium-porphin were determined using basis set functions augmented by both the polarization and diffuse functions-6-31+G(d). Such basis is recommended for correct description of the spectra because diffuse functions play fundamental roles in the formation of Rydberg MOs. The obtained results indicated that already the lowest roots in A(u), B(1u), B(2g), and B(3g) irreducible representations display Rydberg character. The calculated spectra are in a good agreement with both experimental and recently calculated electronic transitions. It is concluded that the SAC/SAC-CI level spectral lines are significantly affected by configuration selection when energy thresholds 5.0 x 10(-6) and 5.0 x 10(-7) a.u. are used for the determination of ground and excited state properties.
Energy Technology Data Exchange (ETDEWEB)
Moradian, Rostam [Physics Department, Faculty of Science, Razi University, Kermanshah (Iran, Islamic Republic of); Nano Science and Technology Research Center, Razi University, Kermanshah (Iran, Islamic Republic of); Computational Physical Science Research Laboratory, Department of Nano Science, Institute for Studies in Theoretical Physics and Mathematics (IPM), PO Box 19395-5531, Tehran (Iran, Islamic Republic of)], E-mail: moradian.rostam@gmail.com; Behzad, Somayeh; Chegel, Raad [Physics Department, Faculty of Science, Razi University, Kermanshah (Iran, Islamic Republic of)
2009-06-15
We present the results of ab initio density functional theory calculations on the energetic, and geometric and electronic structure of Li-intercalated (6,6) silicon carbide nanotube (SiCNT) bundles. Our results show that intercalation of lithium leads to the significant changes in the geometrical structure. The most prominent effect of Li intercalation on the electronic band structure is a shift of the Fermi energy which occurs as a result of charge transfer from lithium to the SiCNTs. All the Li-intercalated (6,6) SiCNT bundles are predicted to be metallic representing a substantial change in electronic properties relative to the undoped bundle, which is a wide band gap semiconductor. Both inside of the nanotube and the interstitial space are susceptible for intercalation. The present calculations suggest that the SiCNT bundle is a promising candidate for the anode material in battery applications.
DEFF Research Database (Denmark)
Bork, Nicolai Christian; Du, Lin; Reiman, Heidi;
2014-01-01
Models of formation and growth of atmospheric aerosols are highly dependent on accurate cluster binding energies. These are most often calculated by ab initio electronic structure methods but remain associated with significant uncertainties. We present a computational benchmarking study......) and compare this range to predictions from several widely used electronic structure methods, including five density functionals, Møller-Plesset perturbation theory, and five coupled cluster methods up to CCSDT quality, considering also the D3 dispersion correctional scheme. With some exceptions, we find...... that most electronic structure methods overestimate ΔG°295 K. The effects of vibrational anharmonicity is approximated using scaling factors, reducing ΔG°295 K by ca. 1.8 kJ mol(-1), whereby ΔG°295 K predictions well within the experimental range can be obtained....
Directory of Open Access Journals (Sweden)
Chelli S.
2015-12-01
Full Text Available The structural, elastic, electronic and thermodynamic properties of BaxSr1−xS ternary alloys have been investigated using the full-potential (linearized augmented plane wave method. The ground state properties, such as lattice constant, bulk modulus and elastic constants, are in good agreement with numerous experimental and theoretical data. The dependence of the lattice parameters, bulk modulus and band gap on the composition x was analyzed. Deviation of the lattice constant from Vegard’s law and the bulk modulus from linear concentration dependence (LCD was observed. The microscopic origins of the gap bowing were explained by using the approach of Zunger et al. The thermodynamic stability of BaxSr1−xS alloy was investigated by calculating the excess enthalpy of mixing, ΔHm and the calculated phase diagram showed a broad miscibility gap with a critical temperature.
Energy Technology Data Exchange (ETDEWEB)
Pustovarov, V. A. [Ural State Technical University (Russian Federation); Aliev, V. Sh.; Perevalov, T. V., E-mail: timson@isp.nsc.ru; Gritsenko, V. A., E-mail: grits@isp.nsc.ru [Russian Academy of Sciences, Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Eliseev, A. P. [Russian Academy of Sciences, Institute of Geology and Mineralogy, Siberian Branch (Russian Federation)
2010-01-15
The electronic structure of an oxygen vacancy in {alpha}-Al{sub 2}O{sub 3} and {gamma}-Al{sub 2}O{sub 3} is calculated. The calculation predicts an absorption peak at an energy of 6.4 and 6.3 eV in {alpha}-Al{sub 2}O{sub 3} and {gamma}-Al{sub 2}O{sub 3}, respectively. The luminescence and luminescence excitation spectra of amorphous Al{sub 2}O{sub 3} are measured using synchrotron radiation. The presence of a luminescence band at 2.9 eV and a peak at 6.2 eV in the luminescence excitation spectrum indicates the presence of oxygen vacancies in amorphous Al{sub 2}O{sub 3}.
Energy Technology Data Exchange (ETDEWEB)
Mahmoud, Nada T.; Khalifeh, Jamil M. [Physics Department, The University of Jordan, Amman 11942 (Jordan); Mousa, Ahmad A., E-mail: amousa@meu.edu.jo [Middle East University, P.O. Box 383, Amman 11831 (Jordan); Juwhari, Hassan K.; Hamad, Bothina A. [Physics Department, The University of Jordan, Amman 11942 (Jordan)
2013-12-01
Density Functional Theory (DFT) calculations of a series of the nonstoichiometric Fe{sub 2−x}Co{sub x}VSn full Heusler alloy were carried out utilizing the full potential linearized augmented plane wave (FP-LAPW) method to investigate the electronic, energetic, and magnetic structures of the above systems. Unlike many concentration curves, increasing the cobalt concentration had a crucial effect on the spin polarization as it flattened at 100% at x=1.50, 1.75, and 2.00 where the half- metallic behavior was located with negative formation energy. Moreover, the total magnetic moment of the host material is found to increase with increasing Co concentration. Finally, the half metallic compounds found in some structures of this series might be useful in spintronic devices.
Titantah, J. T.; Lamoen, D.; Schowalter, M.; Rosenauer, A.
2010-02-01
The atomic scattering amplitudes of the various atoms of the systems Ga1-xInxAs, GaAs1-xNx and InAs1-xNx are calculated using the density functional theory (DFT) approach. The scattering amplitudes of N, Ga, As and In in the model systems are compared with the frequently used Doyle and Turner values. Deviation from the latter values is found for small scattering vectors (sMASAs) for small scattering vectors (sMASAs are exploited within zero pressure classical Metropolis Monte Carlo (MC), finite temperature calculations to investigate the effect of quantum well size on the electron {002} structure factor (SF) of Ga1-xInxAs quantum wells.
Energy Technology Data Exchange (ETDEWEB)
Chen, Chung-De [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30076, Taiwan (China); National Tsing Hua University, Hsinchu, Taiwan (China); Huang, Yen-Chieh [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30076, Taiwan (China); Chiang, Hsin-Lin [National Tsing Hua University, Hsinchu, Taiwan (China); Hsieh, Yin-Cheng; Guan, Hong-Hsiang; Chuankhayan, Phimonphan [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30076, Taiwan (China); Chen, Chun-Jung, E-mail: cjchen@nsrrc.org.tw [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30076, Taiwan (China); National Tsing Hua University, Hsinchu, Taiwan (China); National Cheng Kung University, Tainan City 701, Taiwan (China); National Cheng Kung University, Tainan City 701, Taiwan (China)
2014-09-01
A novel direct phase-selection method to select optimized phases from the ambiguous phases of a subset of reflections to replace the corresponding initial SAD phases has been developed. With the improved phases, the completeness of built residues of protein molecules is enhanced for efficient structure determination. Optimization of the initial phasing has been a decisive factor in the success of the subsequent electron-density modification, model building and structure determination of biological macromolecules using the single-wavelength anomalous dispersion (SAD) method. Two possible phase solutions (ϕ{sub 1} and ϕ{sub 2}) generated from two symmetric phase triangles in the Harker construction for the SAD method cause the well known phase ambiguity. A novel direct phase-selection method utilizing the θ{sub DS} list as a criterion to select optimized phases ϕ{sub am} from ϕ{sub 1} or ϕ{sub 2} of a subset of reflections with a high percentage of correct phases to replace the corresponding initial SAD phases ϕ{sub SAD} has been developed. Based on this work, reflections with an angle θ{sub DS} in the range 35–145° are selected for an optimized improvement, where θ{sub DS} is the angle between the initial phase ϕ{sub SAD} and a preliminary density-modification (DM) phase ϕ{sub DM}{sup NHL}. The results show that utilizing the additional direct phase-selection step prior to simple solvent flattening without phase combination using existing DM programs, such as RESOLVE or DM from CCP4, significantly improves the final phases in terms of increased correlation coefficients of electron-density maps and diminished mean phase errors. With the improved phases and density maps from the direct phase-selection method, the completeness of residues of protein molecules built with main chains and side chains is enhanced for efficient structure determination.
Ab-initio simulations of materials using VASP: Density-functional theory and beyond.
Hafner, Jürgen
2008-10-01
During the past decade, computer simulations based on a quantum-mechanical description of the interactions between electrons and between electrons and atomic nuclei have developed an increasingly important impact on solid-state physics and chemistry and on materials science-promoting not only a deeper understanding, but also the possibility to contribute significantly to materials design for future technologies. This development is based on two important columns: (i) The improved description of electronic many-body effects within density-functional theory (DFT) and the upcoming post-DFT methods. (ii) The implementation of the new functionals and many-body techniques within highly efficient, stable, and versatile computer codes, which allow to exploit the potential of modern computer architectures. In this review, I discuss the implementation of various DFT functionals [local-density approximation (LDA), generalized gradient approximation (GGA), meta-GGA, hybrid functional mixing DFT, and exact (Hartree-Fock) exchange] and post-DFT approaches [DFT + U for strong electronic correlations in narrow bands, many-body perturbation theory (GW) for quasiparticle spectra, dynamical correlation effects via the adiabatic-connection fluctuation-dissipation theorem (AC-FDT)] in the Vienna ab initio simulation package VASP. VASP is a plane-wave all-electron code using the projector-augmented wave method to describe the electron-core interaction. The code uses fast iterative techniques for the diagonalization of the DFT Hamiltonian and allows to perform total-energy calculations and structural optimizations for systems with thousands of atoms and ab initio molecular dynamics simulations for ensembles with a few hundred atoms extending over several tens of ps. Applications in many different areas (structure and phase stability, mechanical and dynamical properties, liquids, glasses and quasicrystals, magnetism and magnetic nanostructures, semiconductors and insulators, surfaces
Sitkiewicz, Sebastian P.; Oliva, Josep M.; Dávalos, Juan Z.; Notario, Rafael; Saiz-Lopez, Alfonso; Alcoba, Diego R.; Oña, Ofelia B.; Roca-Sanjuán, Daniel
2016-12-01
The electronic states of atmospheric relevant molecules IBr and HgBr2 are reported, within the UV-Vis spectrum range (170 nm ≤λp h o t o n≤600 nm) by means of the complete-active-space self-consistent field/multi-state complete-active-space second-order perturbation theory/spin-orbit restricted-active-space state-interaction (CASSCF/MS-CASPT2/SO-RASSI) quantum-chemical approach and atomic-natural-orbital relativistic-correlation-consistent (ANO-RCC) basis sets. Several analyses of the methodology were carried out in order to reach converged results and therefore to establish a highly accurate level of theory. Good agreement is found with the experimental data with errors not higher than around 0.1 eV. The presented analyses shall allow upcoming studies aimed to accurately determine the absorption cross sections of interhalogen molecules and compounds with Hg that are relevant to better comprehend the photochemical processes taking place in the atmosphere.
Ab initio prediction on ferrotoroidic and electronic properties of olivine Li4MnFeCoNiP4O16
Institute of Scientific and Technical Information of China (English)
Feng Hong-Jian; Liu Fa-Min
2009-01-01
First-principles calculations predict that olivine Li4MnFeCoNiP4O16 has a large toroidal moment and ferrimagnetic configuration with a magnetic moment of 1.99μB per formula unit. Density functional theory pins U (DFT+U) shows an indirect band gap of 0.65 eV in this hypothetical material. The band gap is not simply related to the electronic conductivity when it is used as cathode material in rechargeable Li-ion batteries. Based on the orbital-resolved density of states for the transition-metal ions in the hypothetical material, Co, Ni and Mn are in the high-spin configuration while Fe is in the low-spin configuration, which leads to a large resulting toroidal moment deriving from the Co and Ni ions.The spin configuration of the transition-metal ions in the system breaks the space- and time-inversion symmetry and leads to the magnetoelectric property simultaneously. The ferrotoroidic domain, the fourth form of ferroic, is observed in this new material, as in the case of LiCoPO4 reported recently.
Energy Technology Data Exchange (ETDEWEB)
Ivanov, Maxim V.; Perevalov, Timofey V.; Aliev, Vladimir S.; Gritsenko, Vladimir A. [A. V. Rzhanov Institute of Semiconductor Physics SB RAS, Novosibirsk, 630090 (Russian Federation); Kaichev, Vasily V. [Boreskov Institute of Catalysis SB RAS, Novosibirsk, 630090 (Russian Federation)
2011-07-15
Electronic structure of oxygen vacancies in Ta{sub 2}O{sub 5} have been studied theoretically by first-principles calculations and experimentally by x-ray photoelectron spectroscopy. Calculations of {delta}-Ta{sub 2}O{sub 5} were performed using density functional theory within gradient-corrected approximation with the +U approach. Results indicate that the oxygen vacancy causes a defect level in the energy gap at 1.2 eV above the top of the valence band. To produce oxygen vacancies, amorphous films of Ta{sub 2}O{sub 5} were bombarded with Ar{sup +} ions. XPS results indicate that the Ar-ion bombardment leads to the generation of the oxygen vacancies in Ta{sub 2}O{sub 5} that characterize the peak at 2 eV above the valence band. The calculated spectrum of crystalline {delta}-Ta{sub 2}O{sub 5} demonstrates qualitative correspondence with the XPS spectrum of the amorphous Ta{sub 2}O{sub 5} film after Ar-ion bombardment.
Energy Technology Data Exchange (ETDEWEB)
Miloud Abid, O.; Yakoubi, A. [Laboratoire d’Etudes des Matériaux et Instrumentations Expérimentales, Université Djilali Liabes de Sidi Bel-Abbes, 22000 (Algeria); Tadjer, A. [Modeling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, Sidi Bel-Abbes (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 (Algeria); Ahmed, R. [Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, UTM Skudai, 81310 Johor (Malaysia); Murtaza, G. [Materials Modeling Laboratory, Department of Physics, Islamia College University, Peshawar (Pakistan); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Azam, Sikander [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic)
2014-12-15
Highlights: • The calculated structural parameters of RMn{sub 2}Ge{sub 2} (R = Ca, Nd and Y) compounds are found in good agreement with the experimental data. • The structural and band structure calculation reveals that these compounds are ferromagnetic brittle metals. • The elastic and thermodynamic properties for the herein studied compounds are investigated for the first time. - Abstract: Intermetallic RMn{sub 2}Ge{sub 2} ternary compounds have attracted considerable attention from researchers in recent years because they show strong indications for novel magnetic characteristics and they have the potential to reveal the mechanism of superlattices. The study of the paramagnetic, ferromagnetic and antiferromagnetic phases affirms the strong dependence to the distance between atomic species in these compounds. In this study, we investigated the structural, elastic, electronic and thermodynamic properties of the intermetallic RMn{sub 2}Ge{sub 2} (R = Ca, Nd and Y) compounds. To carry out this study, we used the full potential (FP) linearized (L) augmented plane wave plus local orbitals (APW + lo), a scheme of calculations developed within the frame work of density functional theory (DFT). To incorporate the exchange correlation (XC) energy and corresponding potential into the total energy calculations, local density approximation (LDA) parameterized by Perdew and Wang is taken into account. Analysis of the density of states (DOS) profile illustrates the conducting nature of these intermetallic compounds; with a predominantly contribution from the R and Mn-d states. At ambient conditions, calculations for elastic constants (C{sub 11}, C{sub 12}, C{sub 13}, C{sub 44}, C{sub 33} and C{sub 66}) are also performed, which point to their brittle character. In addition, the quasi harmonic Debye model was used to predict the thermal properties, together with relative expansion coefficients and heat capacity.
Thermodynamic assessment of the Ho–Te system supported by ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Ghamri, H.; Belgacem-Bouzida, A. [Laboratoire d’étude Physico-Chimique des Matériaux, Département de Physique, Faculté des Sciences, Université de Batna, Rue Chahid Boukhlouf, 05000 Batna (Algeria); Djaballah, Y., E-mail: ydjaballah@yahoo.fr [Laboratoire d’étude Physico-Chimique des Matériaux, Département de Physique, Faculté des Sciences, Université de Batna, Rue Chahid Boukhlouf, 05000 Batna (Algeria); Hidoussi, A. [Laboratoire d’étude Physico-Chimique des Matériaux, Département de Physique, Faculté des Sciences, Université de Batna, Rue Chahid Boukhlouf, 05000 Batna (Algeria)
2013-03-05
Highlights: ► We calculated enthalpies of formation of the HoTe and Ho{sub 2}Te{sub 5} compounds by using ab initio method. ► We modeled the Gibbs energy of the HoTe intermediate phase for the first time. ► The thermodynamic parameters of the all phases existing in the system were determined. ► The complete phase diagram of the system (Ho–Te) is calculated. -- Abstract: The phase diagram of the Ho–Te binary system has been assessed by using the CALPHAD (Calculation of Phase Diagrams) method on the basis of the experimental data of the phase equilibria and enthalpies of formation from ab initio electronic-structure calculations within the framework of density-functional theory. Reasonable models were constructed for all the phases of the system. The liquid phase was described as the substitutional solution model with excess energy expressed by Redlich–Kister polynomial. The compounds Ho{sub 2}Te{sub 5} and HoTe{sub 3} were expressed as stoichiometric phases. The (HoTe) phase was modeled by two-sublattices; (Ho,Va){sub 1}(Te){sub 1}. A consistent set of thermodynamic parameters has been derived, and calculated phase diagram was compared with the experimental data. A good agreement between the calculated results and experimental data was obtained.
Experimental and ab initio investigations on textured Li–Mn–O spinel thin film cathodes
Energy Technology Data Exchange (ETDEWEB)
Fischer, J., E-mail: Julian.Fischer@kit.edu [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Music, D. [RWTH Aachen University, Materials Chemistry, Kopernikusstrasse 10, 52074 Aachen (Germany); Bergfeldt, T.; Ziebert, C.; Ulrich, S.; Seifert, H.J. [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)
2014-12-01
This paper describes the tailored preparation of nearly identical lithium–manganese–oxide thin film cathodes with different global grain orientations. The thin films were synthesized by rf magnetron sputtering from a LiMn{sub 2}O{sub 4}-target in a pure argon plasma. Under appropriate processing conditions, thin films with a cubic spinel structure and a nearly similar density and surface topography but different grain orientation, i.e. (111)- and (440)-textured films, were achieved. The chemical composition was determined by inductively coupled plasma optical emission spectroscopy and carrier gas hot extraction. The constitution- and microstructure were evaluated by X-ray diffraction and Raman spectroscopy. The surface morphology and roughness were investigated by scanning electron and atomic force microscopy. The differently textured films represent an ideal model system for studying potential effects of grain orientation on the lithium ion diffusion and electrochemical behavior in LiMn{sub 2}O{sub 4}-based thin films. They are nearly identical in their chemical composition, atomic bonding behavior, surface-roughness, morphology and thickness. Our initial ab initio molecular dynamics data indicate that Li ion transport is faster in (111)-textured structure than in (440)-textured one. - Highlights: • Thin film model system of differently textured cubic Li–Mn–O spinels. • Investigation of the Li–Mn–O thin film mass density by X-ray reflectivity. • Ab initio molecular dynamics simulation on Li ion diffusion in LiMn{sub 2}O{sub 4}.
Embedding parameters in ab initio theory to develop approximations based on molecular similarity
Tanha, Matteus; Kaul, Shiva; Cappiello, Alexander; Gordon, Geoffrey J; Yaron, David J
2015-01-01
A means to take advantage of molecular similarity to lower the computational cost of electronic structure theory is explored, in which parameters are embedded into a low-cost, low-level (LL) ab initio model and adjusted to obtain agreement with results from a higher-level (HL) ab initio model. A parametrized LL (pLL) model is created by multiplying selected matrix elements of the Hamiltonian operators by scaling factors that depend on element types. Various schemes for applying the scaling factors are compared, along with the impact of making the scaling factors linear functions of variables related to bond lengths, atomic charges, and bond orders. The models are trained on ethane and ethylene, substituted with -NH2, -OH and -F, and tested on substituted propane, propylene and t-butane. Training and test datasets are created by distorting the molecular geometries and applying uniform electric fields. The fitted properties include changes in total energy arising from geometric distortions or applied fields, an...
Ab initio calculation of oxygen self-diffusion coefficient in uranium dioxide UO2
Dorado, Boris; Garcia, Philippe; Torrent, Marc
Uranium dioxide UO2 is the most widely used nuclear fuel worldwide and its atomic transport properties are relevant to practically all engineering aspects of the material. Although transport properties have already been studied in UO2 by means of first-principles calculations, the ab initio determination of self-diffusion coefficients has up to now remained unreachable because the relevant computational tools were neither available or adapted. The present work reports our results related to the ab initio calculation of the oxygen self-diffusion coefficient in UO2. We first determine the Gibbs free energies of formation of oxygen charged defects by calculating both the electronic and vibrational (hence entropic) contributions. Then, we use the transition state theory in order to compute the effective jump frequency of the defects, which in turn provides us with the value of the pre-exponential factor. The results are compared to self-diffusion data obtained experimentally with a careful monitoring of the relevant thermodynamic conditions (oxygen partial pressure, temperature, impurity content).
Ground state analytical ab initio intermolecular potential for the Cl{sub 2}-water system
Energy Technology Data Exchange (ETDEWEB)
Hormain, Laureline; Monnerville, Maurice, E-mail: maurice.monnerville@univ-lille1.fr; Toubin, Céline; Duflot, Denis; Pouilly, Brigitte; Briquez, Stéphane [Laboratoire de Physique des Lasers Atomes et Molécules, Unité Mixte de Recherche (UMR) 8523, Université Lille I, Bât. P5, 59655 Villeneuve d’Ascq Cedex (France); Bernal-Uruchurtu, Margarita I.; Hernández-Lamoneda, Ramón [Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Cuernavaca 62209, México (Mexico)
2015-04-14
The chlorine/water interface is of crucial importance in the context of atmospheric chemistry. Modeling the structure and dynamics at this interface requires an accurate description of the interaction potential energy surfaces. We propose here an analytical intermolecular potential that reproduces the interaction between the Cl{sub 2} molecule and a water molecule. Our functional form is fitted to a set of high level ab initio data using the coupled-cluster single double (triple)/aug-cc-p-VTZ level of electronic structure theory for the Cl{sub 2} − H{sub 2}O complex. The potential fitted to reproduce the three minima structures of 1:1 complex is validated by the comparison of ab initio results of Cl{sub 2} interacting with an increasing number of water molecules. Finally, the model potential is used to study the physisorption of Cl{sub 2} on a perfectly ordered hexagonal ice slab. The calculated adsorption energy, in the range 0.27 eV, shows a good agreement with previous experimental results.
Lithium Insertion In Silicon Nanowires: An ab Initio Study
Zhang, Qianfan
2010-09-08
The ultrahigh specific lithium ion storage capacity of Si nanowires (SiNWs) has been demonstrated recently and has opened up exciting opportunities for energy storage. However, a systematic theoretical study on lithium insertion in SiNWs remains a challenge, and as a result, understanding of the fundamental interaction and microscopic dynamics during lithium insertion is still lacking. This paper focuses on the study of single Li atom insertion into SiNWs with different sizes and axis orientations by using full ab initio calculations. We show that the binding energy of interstitial Li increases as the SiNW diameter grows. The binding energies at different insertion sites, which can be classified as surface, intermediate, and core sites, are quite different. We find that surface sites are energetically the most favorable insertion positions and that intermediate sites are the most unfavorable insertion positions. Compared with the other growth directions, the [110] SiNWs with different diameters always present the highest binding energies on various insertion locations, which indicates that [110] SiNWs are more favorable by Li doping. Furthermore, we study Li diffusion inside SiNWs. The results show that the Li surface diffusion has a much higher chance to occur than the surface to core diffusion, which is consistent with the experimental observation that the Li insertion in SiNWs is layer by layer from surface to inner region. After overcoming a large barrier crossing surface-to-intermediate region, the diffusion toward center has a higher possibility to occur than the inverse process. © 2010 American Chemical Society.
Efficient conformational space exploration in ab initio protein folding simulation.
Ullah, Ahammed; Ahmed, Nasif; Pappu, Subrata Dey; Shatabda, Swakkhar; Ullah, A Z M Dayem; Rahman, M Sohel
2015-08-01
Ab initio protein folding simulation largely depends on knowledge-based energy functions that are derived from known protein structures using statistical methods. These knowledge-based energy functions provide us with a good approximation of real protein energetics. However, these energy functions are not very informative for search algorithms and fail to distinguish the types of amino acid interactions that contribute largely to the energy function from those that do not. As a result, search algorithms frequently get trapped into the local minima. On the other hand, the hydrophobic-polar (HP) model considers hydrophobic interactions only. The simplified nature of HP energy function makes it limited only to a low-resolution model. In this paper, we present a strategy to derive a non-uniform scaled version of the real 20×20 pairwise energy function. The non-uniform scaling helps tackle the difficulty faced by a real energy function, whereas the integration of 20×20 pairwise information overcomes the limitations faced by the HP energy function. Here, we have applied a derived energy function with a genetic algorithm on discrete lattices. On a standard set of benchmark protein sequences, our approach significantly outperforms the state-of-the-art methods for similar models. Our approach has been able to explore regions of the conformational space which all the previous methods have failed to explore. Effectiveness of the derived energy function is presented by showing qualitative differences and similarities of the sampled structures to the native structures. Number of objective function evaluation in a single run of the algorithm is used as a comparison metric to demonstrate efficiency.
Cosmic-Ray Modulation: an Ab Initio Approach
Engelbrecht, N. E.; Burger, R. A.
2014-10-01
A better understanding of cosmic-ray modulation in the heliosphere can only be gained through a proper understanding of the effects of turbulence on the diffusion and drift of cosmic rays. We present an ab initio model for cosmic-ray modulation, incorporating for the first time the results yielded by a two-component turbulence transport model. This model is solved for periods of minimum solar activity, utilizing boundary values chosen so that model results are in fair to good agreement with spacecraft observations of turbulence quantities, not only in the solar ecliptic plane but also along the out-of-ecliptic trajectory of the Ulysses spacecraft. These results are employed as inputs for modelled slab and 2D turbulence energy spectra. The latter spectrum is chosen based on physical considerations, with a drop-off at the very lowest wavenumbers commencing at the 2D outerscale. There currently exist no models or observations for this quantity, and it is the only free parameter in this study. The modelled turbulence spectra are used as inputs for parallel mean free path expressions based on those derived from quasi-linear theory and perpendicular mean free paths from extended nonlinear guiding center theory. Furthermore, the effects of turbulence on cosmic-ray drifts are modelled in a self-consistent way, employing a recently developed model for drift along the wavy current sheet. The resulting diffusion coefficients and drift expressions are applied to the study of galactic cosmic-ray protons and antiprotons using a three-dimensional, steady-state cosmic-ray modulation code, and sample solutions in fair agreement with multiple spacecraft observations are presented.
i-PI: A Python interface for ab initio path integral molecular dynamics simulations
Ceriotti, Michele; More, Joshua; Manolopoulos, David E.
2014-03-01
Recent developments in path integral methodology have significantly reduced the computational expense of including quantum mechanical effects in the nuclear motion in ab initio molecular dynamics simulations. However, the implementation of these developments requires a considerable programming effort, which has hindered their adoption. Here we describe i-PI, an interface written in Python that has been designed to minimise the effort required to bring state-of-the-art path integral techniques to an electronic structure program. While it is best suited to first principles calculations and path integral molecular dynamics, i-PI can also be used to perform classical molecular dynamics simulations, and can just as easily be interfaced with an empirical forcefield code. To give just one example of the many potential applications of the interface, we use it in conjunction with the CP2K electronic structure package to showcase the importance of nuclear quantum effects in high-pressure water. Catalogue identifier: AERN_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AERN_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.: 138626 No. of bytes in distributed program, including test data, etc.: 3128618 Distribution format: tar.gz Programming language: Python. Computer: Multiple architectures. Operating system: Linux, Mac OSX, Windows. RAM: Less than 256 Mb Classification: 7.7. External routines: NumPy Nature of problem: Bringing the latest developments in the modelling of nuclear quantum effects with path integral molecular dynamics to ab initio electronic structure programs with minimal implementational effort. Solution method: State-of-the-art path integral molecular dynamics techniques are implemented in a Python interface. Any electronic structure code can be patched to receive the atomic
2015-01-01
Colloidal quantum dots (QDs) exhibit highly desirable size- and shape-dependent properties for applications from electronic devices to imaging. Indium phosphide QDs have emerged as a primary candidate to replace the more toxic CdSe QDs, but production of InP QDs with the desired properties lags behind other QD materials due to a poor understanding of how to tune the growth process. Using high-temperature ab initio molecular dynamics (AIMD) simulations, we report the first direct observation o...
Ab initio interaction potentials for X and B excited states of He-I{sub 2} for studying dynamics
Energy Technology Data Exchange (ETDEWEB)
Prosmiti, Rita; Garcia-Gutierrez, Leonor; Delgado-Tellez, Laura; Valdes, Alvaro; Villarreal, Pablo; Delgado-Barrio, Gerardo, E-mail: rita@imaff.cfmac.csic.e [Instituto de Fisica Fundamental (CSIC), Serrano 123, 28006 Madrid (Spain)
2009-11-01
Ab initio CCSD(T) and MRCI approaches were employed to construct potential energy surfaces of the ground and the B electronic excited states of He-I{sub 2} complex, while full quantum mechanical methods were applied to study its spectroscopy and dynamics. A description of the approach adopted, together with the results obtained and their comparison with recent experimental data, as well as further improvements are presented.
Estudo ab-initio da a-alanina em meio aquoso
Directory of Open Access Journals (Sweden)
Sambrano Júlio Ricardo
1999-01-01
Full Text Available Ab initio Hartree-Fock (HF, Density Functional (B3LYP and electron correlation (MP2 methods have been used to caracterize the aqueous medium intramolecular hydrogen bond in a-alanine. The 6-31G* and 6-31++G** were taken from Gaussian94 library. We were concerned on the structure of three conformers of a-alanine, in their neutral form plus on the structure of the zwitterionic form (Z. The Z structure is a stationary point at the HF/6-31G* level but it is not when diffuse functions and electron correlation are included. This results shows that the Z form does not exist in the gas phase. The inclusion of solvent effects changed significantly the results obtained in gas phase, therefore this inclusion make the Z form a stationary point within all level of theory, and the relative energy depends dramatically on the level of calculation.
Ab initio approach to the ion stopping power at the plasma-solid interface
Bonitz, Michael; Schlünzen, Niclas; Wulff, Lasse; Joost, Jan-Philip; Balzer, Karsten
2016-10-01
The energy loss of ions in solids is of key relevance for many applications of plasmas, ranging from plasma technology to fusion. Standard approaches are based on density functional theory or SRIM simulations, however, the applicability range and accuracy of these results are difficult to assess, in particular, for low energies. Here we present an independent approach that is based on ab initio nonequilibrium Green functions theory, e.g. that allows to incorporate electronic correlations effects of the solid. We present the first application of this method to low-temperature plasmas, concentrating on proton and alpha-particle stopping in a graphene layer. In addition to the stopping power we present time-dependent results for the local electron density, the spectral function and the photoemission spectrum that is directly accessible in optical, UV or x-ray diagnostics. http://www.itap.uni-kiel.de/theo-physik/bonitz/.
Ab initio modeling of radiation damage in MgF{sub 2} crystals
Energy Technology Data Exchange (ETDEWEB)
Abuova, F.U. [L. N. Gumilyov Eurasian National University, 3 Munaitpasova Str., Astana (Kazakhstan); Kotomin, E.A., E-mail: kotomin@latnet.lv [Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., LV-1063, Riga (Latvia); Lisitsyn, V.M. [Tomsk Polytechnical University, Tomsk 634003 (Russian Federation); Akilbekov, A.T. [L. N. Gumilyov Eurasian National University, 3 Munaitpasova Str., Astana (Kazakhstan); Piskunov, S. [Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str., LV-1063, Riga (Latvia)
2014-05-01
MgF{sub 2} with a rutile structure is important radiation-resistant material with numerous applications due to its transparency from vacuum ultraviolet to infrared range of photon energies. We present and discuss the results of calculations for basic radiation defects in this crystal. The study is based on the large scale ab initio DFT calculations using hybrid B3PW exchange–correlation functional and atomic basis set. We analyzed the electronic structure, atomic displacements, charge density distribution as well as defect formation energies using large supercells. We compared properties of close and well separated F−H (Frenkel) defect pairs as well as individual defects. We simulated also formation and energetic preference of inert F{sub 2} interstitial molecules as sinks of mobile interstitial fluorine atoms which is relevant for material radiation stability. We discussed also diffusion of the primary electronic defects—F centers.
Communication: Improved ab initio molecular dynamics by minimally biasing with experimental data
White, Andrew D.; Knight, Chris; Hocky, Glen M.; Voth, Gregory A.
2017-01-01
Accounting for electrons and nuclei simultaneously is a powerful capability of ab initio molecular dynamics (AIMD). However, AIMD is often unable to accurately reproduce properties of systems such as water due to inaccuracies in the underlying electronic density functionals. This shortcoming is often addressed by added empirical corrections and/or increasing the simulation temperature. We present here a maximum-entropy approach to directly incorporate limited experimental data via a minimal bias. Biased AIMD simulations of water and an excess proton in water are shown to give significantly improved properties both for observables which were biased to match experimental data and for unbiased observables. This approach also yields new physical insight into inaccuracies in the underlying density functional theory as utilized in the unbiased AIMD.
i-PI: A Python interface for ab initio path integral molecular dynamics simulations
Ceriotti, Michele; Manolopoulos, David E
2014-01-01
Recent developments in path integral methodology have significantly reduced the computational expense of including quantum mechanical effects in the nuclear motion in ab initio molecular dynamics simulations. However, the implementation of these developments requires a considerable programming effort, which has hindered their adoption. Here we describe i-PI, an interface written in Python that has been designed to minimise the effort required to bring state-of-the-art path integral techniques to an electronic structure program. While it is best suited to first principles calculations and path integral molecular dynamics, i-PI can also be used to perform classical molecular dynamics simulations, and can just as easily be interfaced with an empirical forcefield code. To give just one example of the many potential applications of the interface, we use it in conjunction with the CP2K electronic structure package to showcase the importance of nuclear quantum effects in high pressure water.
Ab initio research of stopping power for energetic ions in solids
He, Bin; Meng, Xu-Jun; Wang, Jian-Guo
2017-03-01
A new physical scenario is suggested to estimate the stopping power of energetic α particles in solid-density Be, Na, and Al at room temperature in an ab initio way based on the average atom model. In the scenario the stopping power is caused by the transition of free electrons to higher energy states and the ionization of bound electrons of the atom. Our results are found generally in good agreement with the recommended data in Al, Be and Na as well as the experimental data in Al. A comparison of energy loss with the recent experiment of protons in Be indicates that the scenario is more reasonable than the local density approximation in this case.
Ab initio theory for ultrafast magnetization dynamics with a dynamic band structure
Mueller, B. Y.; Haag, M.; Fähnle, M.
2016-09-01
Laser-induced modifications of magnetic materials on very small spatial dimensions and ultrashort timescales are a promising field for novel storage and spintronic devices. Therefore, the contribution of electron-electron spin-flip scattering to the ultrafast demagnetization of ferromagnets after an ultrashort laser excitation is investigated. In this work, the dynamical change of the band structure resulting from the change of the magnetization in time is taken into account on an ab initio level. We find a large influence of the dynamical band structure on the magnetization dynamics and we illustrate the thermalization and relaxation process after laser irradiation. Treating the dynamical band structure yields a demagnetization comparable to the experimental one.
An investigation of ab initio shell-model interactions derived by no-core shell model
Wang, XiaoBao; Dong, GuoXiang; Li, QingFeng; Shen, CaiWan; Yu, ShaoYing
2016-09-01
The microscopic shell-model effective interactions are mainly based on the many-body perturbation theory (MBPT), the first work of which can be traced to Brown and Kuo's first attempt in 1966, derived from the Hamada-Johnston nucleon-nucleon potential. However, the convergence of the MBPT is still unclear. On the other hand, ab initio theories, such as Green's function Monte Carlo (GFMC), no-core shell model (NCSM), and coupled-cluster theory with single and double excitations (CCSD), have made many progress in recent years. However, due to the increasing demanding of computing resources, these ab initio applications are usually limited to nuclei with mass up to A = 16. Recently, people have realized the ab initio construction of valence-space effective interactions, which is obtained through a second-time renormalization, or to be more exactly, projecting the full-manybody Hamiltonian into core, one-body, and two-body cluster parts. In this paper, we present the investigation of such ab initio shell-model interactions, by the recent derived sd-shell effective interactions based on effective J-matrix Inverse Scattering Potential (JISP) and chiral effective-field theory (EFT) through NCSM. In this work, we have seen the similarity between the ab initio shellmodel interactions and the interactions obtained by MBPT or by empirical fitting. Without the inclusion of three-body (3-bd) force, the ab initio shell-model interactions still share similar defects with the microscopic interactions by MBPT, i.e., T = 1 channel is more attractive while T = 0 channel is more repulsive than empirical interactions. The progress to include more many-body correlations and 3-bd force is still badly needed, to see whether such efforts of ab initio shell-model interactions can reach similar precision as the interactions fitted to experimental data.
Malbon, Christopher L.; Zhu, Xiaolei; Guo, Hua; Yarkony, David R.
2016-12-01
For two electronic states coupled by conical intersections, the line integral of the derivative coupling can be used to construct a complex-valued multiplicative phase factor that makes the real-valued adiabatic electronic wave function single-valued, provided that the curl of the derivative coupling is zero. Unfortunately for ab initio determined wave functions, the curl is never rigorously zero. However, when the wave functions are determined from a coupled two diabatic state Hamiltonian Hd (fit to ab initio data), the resulting derivative couplings are by construction curl free, except at points of conical intersection. In this work we focus on a recently introduced diabatization scheme that produces the Hd by fitting ab initio determined energies, energy gradients, and derivative couplings to the corresponding Hd determined quantities in a least squares sense, producing a removable approximation to the ab initio determined derivative coupling. This approach and related numerical issues associated with the nonremovable ab initio derivative couplings are illustrated using a full 33-dimensional representation of phenol photodissociation. The use of this approach to provide a general framework for treating the molecular Aharonov Bohm effect is demonstrated.
Energy Technology Data Exchange (ETDEWEB)
Palacios, P. [Instituto de Energia Solar and Dpt. de Tecnologias Especiales, ETSI de Telecomunicacion, UPM. Ciudad Universitaria s/n, 28040 Madrid (Spain); Instituto de Catalisis y Petroleoquimica, CSIC. Marie Curie 2, Cantoblanco, 28049 Madrid (Spain)], E-mail: pablop@etsit.upm.es; Aguilera, I.; Wahnon, P. [Instituto de Energia Solar and Dpt. de Tecnologias Especiales, ETSI de Telecomunicacion, UPM. Ciudad Universitaria s/n, 28040 Madrid (Spain)
2008-08-30
In this work, we present frozen phonon and linear response ab-initio research into the vibrational properties of the CuGaS{sub 2} chalcopyrite and transition metal substituted (CuGaS{sub 2})M alloys. These systems are potential candidates for developing a novel solar-cell material with enhanced optoelectronic properties based in the implementation of the intermediate-band concept. We have previously carried out ab-initio calculations of the electronic properties of these kinds of chalcopyrite metal alloys showing a narrow transition metal band isolated in the semiconductor band gap. The substitutes used in the present work are the 3d metal elements, Titanium and Chromium. For the theoretical calculations we use standard density functional theory at local density and generalized gradient approximation levels. We found that the optical phonon branches of the transition metal chalcopyrite, are very sensitive to the specific bonding geometry and small changes in the transition metal environment.
Realization of prediction of materials properties by ab initio computer simulation
Indian Academy of Sciences (India)
Yoshiyuki Kawazoe
2003-01-01
Ab initio treatment is becoming realistic to predict physical, chemical, and even mechanical properties of academically and industrially interesting materials. There is, however, some limitation in size and time of the system up to the order of several hundred atoms and ∼ 1 pico second, even if we use the fastest supercomputer efficiently. Therefore, it is very difficult to simulate realistic materials with grain boundaries and important reactions like diffusion in materials. To improve this situation, two ways have been invented. One way is to upgrade approximations to match the necessary levels according to inhomogeneous electron gas theory beyond the present day standard, i.e. local density approximation (LDA). The reason is simply that the system we are interested in is composed of many particles interacting with Coulomb forces governed by quantum mechanics. (Complete knowledge is available, and only what we should do is to make better approximations to explain the phenomena!). Another is to extract the necessary parameters from the ab initio calculations on systems with limited number of atoms, and apply these results into cluster variation, direct, or any other sophisticated methods based on classical concepts such as statistical mechanics. In this paper, several typical examples recently worked out by our research group are introduced to indicate that these methodologies are actually possible to be successfully used to predict materials properties before experiments based on the present day state-of-art supercomputing systems. It includes scientific visualization of the results of ab initio molecular dynamics simulation on atom insertion process to C60 and to carbon nanotube, tight-binding calculation of single electron conductance properties in nanotube to create nano-scale diode virtually by computer, which will be a base of future nanoscale electric device in nanometer size, Li + H reaction without Born–Oppenheimer approximation, structural phase
Heuvel, Willem Van den; Soncini, Alessandro
2015-01-01
We present an ab initio methodology dedicated to the determination of the electronic structure and magnetic properties of ground and low-lying excited states, i.e., the crystal field levels, in lanthanide(III) complexes. Currently, the most popular and successful ab initio approach is the CASSCF/RASSI-SO method, consisting of the optimization of multiple complete active space self-consistent field (CASSCF) spin eigenfunctions, followed by full diagonalization of the spin--orbit coupling (SOC) Hamiltonian in the basis of the CASSCF spin states featuring spin-dependent orbitals. Based on two simple observations valid for Ln(III) complexes, namely: (i) CASSCF 4f atomic orbitals are expected to change very little when optimized for different multiconfigurational states belonging to the 4f-electronic configuration, (ii) due to strong SOC the total spin is not a good quantum number, we propose here an efficient ab initio strategy which completely avoids any multiconfigurational calculation, by optimizing a unique s...
Energy Technology Data Exchange (ETDEWEB)
Reshak, Ali Hussain, E-mail: maalidph@yahoo.co.uk [Institute of Physical Biology-South Bohemia University, Nove Hrady 37333 (Czech Republic); School of Material Engineering, Malaysia University of Perlis, P.O Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis (Malaysia); Kityk, I.V. [Electrical Engineering Department, Technical University of Czestochowa, Al. Armii Krajowej 17/19, Czestochowa (Poland); Khenata, R. [Laboratoire de Physique Quantique et de Modelisation Mathematique de la Matiere (LPQ3 M), universite de Mascara, Mascara 29000 (Algeria); Department of Physics and Astronomy, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Auluck, S. [National Physical Laboratory Dr. K S Krishnan Marg, New Delhi 110012 (India)
2011-06-16
Highlights: > Theoretical study of effect of vary Te content on band structure, density of states, linear and nonlinear optical susceptibilities of CdSe{sub 1-x}Te{sub x}. > Increasing Te content leads to a decrease in the energy band gap. > Significant enhancement of the electronic properties as a function of tellurium concentration - Abstract: An all electron full potential linearized augmented plane wave method, within a framework of GGA (EV-GGA) approach, has been used for an ab initio theoretical study of the effect of increasing tellurium content on the band structure, density of states, and the spectral features of the linear and nonlinear optical susceptibilities of the cadmium-selenide-telluride ternary alloys CdSe{sub 1-x}Te{sub x} (x = 0.0, 0.25, 0.5, 0.75 and 1.0). Our calculations show that increasing Te content leads to a decrease in the energy band gap. We find that the band gaps are 0.95 (1.76), 0.89 (1.65), 0.83 (1.56), 0.79 (1.44) and 0.76 (1.31) eV for x = 0.0, 0.25, 0.5, 0.75 and 1.0 in the cubic structure. As these alloys are known to have a wurtzite structure for x less than 0.25, the energy gaps are 0.8 (1.6) eV and 0.7 (1.55) eV for the wurtzite structure (x = 0.0, 0.25) for the GGA (EV-GGA) exchange correlation potentials. This reduction in the energy gaps enhances the functionality of the CdSe{sub 1-x}Te{sub x} alloys, at least for these concentrations, leading to an increase in the effective second-order susceptibility coefficients from 16.75 pm/V (CdSe) to 18.85 pm/V (CdSe{sub 0.75}Te{sub 0.25}), 27.23 pm/V (CdSe{sub 0.5}Te{sub 0.5}), 32.25 pm/V (CdSe{sub 0.25}Te{sub 0.75}), and 37.70 pm/V (CdTe) for the cubic structure and from 12.65 pm/V (CdSe) to 21.11 pm/V (CdSe{sub 0.75}Te{sub 0.25}) in the wurtzite structure. We find a nonlinear relationship between the absorption/emission energies and composition, and a significant enhancement of the electronic properties as a function of tellurium concentration. This variation will help in
Femtosecond Laser Processing of Germanium: An Ab Initio Molecular Dynamics Study
Ji, Pengfei
2016-01-01
An ab initio molecular dynamics study of femtosecond laser processing of germanium is presented in this paper. The method based on the finite temperature density functional theory is adopted to probe the structural change, thermal motion of the atoms, dynamic property of the velocity autocorrelation, and the vibrational density of states. Starting from a cubic system at room temperature (300 K) containing 64 germanium atoms with an ordered arrangement of 1.132 nm in each dimension, the femtosecond laser processing is simulated by imposing the Nose Hoover thermostat to the electronic subsystem lasting for ~100 fs and continuing with microcanonical ensemble simulation of ~200 fs. The simulation results show solid, liquid and gas phases of germanium under adjusted intensities of the femtosecond laser irradiation. We find the irradiated germanium distinguishes from the usual germanium crystal by analyzing their melting and dynamic properties.
Relaxation of the excited -(2-hydroxy benzylidene) aniline molecule: An ab initio and TD DFT study
Indian Academy of Sciences (India)
Biswajit Chowdhury; Rina De; Pinaky Sett; Joydeep Chowdhury
2010-11-01
The photophysical behaviour of N-(2-hydroxy benzylidene) aniline or most commonly known as salicylideneaniline (SA) has been investigated using the ab initio and DFT levels of theory. The quantum chemical calculations show that the optimized non planar enol (1) form of the SA molecule is the most stable conformer in the ground state and is marked by the twisting of the phenolic and anilino rings of the molecule. The geometry optimizations and the subsequent frequency calculations of the excited singlet electronic states of the various tautomeric forms of SA molecule were performed with the CIS level of theory. A detail theoretical investigation on the relaxation dynamics of the SA molecule has been presented. Possible explanation on the excitation wavelength dependence of the photochromic yield of the molecule is also reported.
Ab-initio molecular dynamics study of lanthanides in liquid sodium
Li, Xiang; Samin, Adib; Zhang, Jinsuo; Unal, C.; Mariani, R. D.
2017-02-01
To mitigate the fuel cladding chemical interaction (FCCI) phenomena in liquid sodium cooled fast reactors, a fundamental understanding of the lanthanide (Ln) transport through liquid Nasbnd Cs filled pores in Usbnd Zr fuel is necessary. In this study, we investigate three abundant Ln fission products diffusion coefficients in liquid Na at multiple temperatures. By utilization of Ab-initio Molecular Dynamics, the Ln diffusivities are found to be in the magnitude order of liquid diffusion (10-5cm2 /s) and the temperature dependence of the diffusivity for different lanthanides in liquid sodium was explored. It is also observed that dilute concentration of Pr and Nd led to a significant change in Na diffusivity. The structural and electronic properties of Nasbnd Ln metallic systems have been investigated. The total coordination number shows dependence on both the temperature and the composition.
Rafiee, Marjan A; Hadipour, Nasser L; Naderi-manesh, Hossein
2004-03-01
In this paper, ab initio calculated NQR parameters for some quinoline-containing derivatives are presented. The calculations are carried out in a search for the relationships between the charge distribution of these compounds and their ability to interact with haematin. On the basis of NQR parameters, pi-electron density on the nitrogen atom of the quinoline ring plays a dominant role in determining the ability of quinolines to interact with haematin. This point was confirmed with investigation of Fe+3 cation-pi quinoline ring interactions in 2- and 4-aminoquinoline. However, our results do not show any preference for those carbon atoms of the quinoline ring which previous reports have noted. In order to calculate the NQR parameters, the electric field gradient (EFG) should be evaluated at the site of a quadrupolar nucleus in each compound. EFGs are calculated by the Gaussian 98 program using the B3LYP/6-31 G* level of theory.
Ab-initio study of magnetism behavior in TiO2 semiconductor with structural defects
Zarhri, Z.; Houmad, M.; Ziat, Y.; El Rhazouani, O.; Slassi, A.; Benyoussef, A.; El Kenz, A.
2016-05-01
Magnetic, electronic and structural properties of titanium dioxide material with different structural defects are studied using the first-principles ab-initio calculations and the Korringa-Kohn-Rostoker method (KKR) combined with the coherent potential approximation (CPA) method in connection with the local density approximation (LDA). We investigated all structural defects in rutile TiO2 such as Titanium interstitial (Tii), Titanium anti-sites (Tio), Titanium vacancies (VTi), Oxygen interstitial (Oi), Oxygen anti-sites (OTi) and oxygen vacancies (Vo). Mechanisms of hybridization and interaction between magnetic atoms are investigated. The transition temperature is computed using the Mean Field Approximation (MFA).Magnetic stability energy of ferromagnetic and disordered local moment states is calculated to determine the most stable state. Titanium anti-sites have a half-metallic aspect. We also studied the change type caused by structural defects in this material.
Structure and lattice dynamics of rare-earth ferroborate crystals: Ab initio calculation
Chernyshev, V. A.; Nikiforov, A. E.; Petrov, V. P.; Serdtsev, A. V.; Kashchenko, M. A.; Klimin, S. A.
2016-08-01
The ab initio calculation of the crystal structure and the phonon spectrum of crystals RFe3(BO3)4 ( R = Pr, Nd, Sm) has been performed in the framework of the density functional theory. The ion coordinates in the unit cell, the lattice parameters, the frequencies and the types of fundamental vibrations, and also the intensities of lines in the Raman spectrum and infrared reflection spectra have been found. The elastic constants of the crystals have been calculated. For low-frequency A 2 mode in PrFe3(BO3)4, a "seed" vibration frequency that strongly interacts with the electronic excitation on a praseodymium ion was found. The calculation results satisfactory agree with the experimental data.
Dadsetani, Mehrdad; Nejatipour, Hajar; Ebrahimian, Ali
2015-05-01
Using the ab initio methods for solving the Bethe-Salpeter equation on the basis of the FPLAPW method, optical properties of crystalline phenanthrene were calculated, in a comparison to its isomer, anthracene. It was found that despite the similarity of the structural, electronic, and the overall optical properties in a 40 eV energy range, phenanthrene and anthracene show significant differences in their optical spectra in the energy range below band gaps. Phenanthrene has two spin singlet excitonic features whereas anthracene shows one. The singlet and the lowest triplet binding energies of phenanthrene were found to be larger than anthracene. In this study, in addition, a comparison has been made between the optical spectra in RPA and the existing experimental data.
Wachter, Georg; Lemell, Christoph; Burgdörfer, Joachim; Sato, Shunsuke A.; Tong, Xiao-Min; Yabana, Kazuhiro
2014-08-01
We theoretically investigate the generation of ultrafast currents in insulators induced by strong few-cycle laser pulses. Ab initio simulations based on time-dependent density functional theory give insight into the atomic-scale properties of the induced current signifying a femtosecond-scale insulator-metal transition. We observe the transition from nonlinear polarization currents during the laser pulse at low intensities to tunnelinglike excitation into the conduction band at higher laser intensities. At high intensities, the current persists after the conclusion of the laser pulse considered to be the precursor of the dielectric breakdown on the femtosecond scale. We show that the transferred charge sensitively depends on the orientation of the polarization axis relative to the crystal axis, suggesting that the induced charge separation reflects the anisotropic electronic structure. We find good agreement with very recent experimental data on the intensity and carrier-envelope phase dependence [A. Schiffrin et al., Nature (London) 493, 70 (2013)].
High-pressure elastic properties of cubic Ir2P from ab initio calculations
Sun, Xiao-Wei; Bioud, Nadhira; Fu, Zhi-Jian; Wei, Xiao-Ping; Song, Ting; Li, Zheng-Wei
2016-10-01
A study of the high-pressure elastic properties of new synthetic Ir2P in the anti-fluorite structure is conducted using ab initio calculations based on density functional theory. The elastic constants C11, C12 and C44 for the cubic Ir2P are obtained by the stress-strain method and the elastic stability calculations under pressure indicate that it is stable at least 100 GPa. Additionally, the electronic density of states, the aggregate elastic moduli, that is bulk modulus, shear modulus, and Young's modulus along with the Debye temperature, Poisson's ratio, and elastic anisotropy factor are all successfully obtained. Moreover, the pressure dependence of the longitudinal and shear wave velocities in three different directions [100], [110], and [111] for Ir2P are also predicted for the first time.
Iftimie, R; Schofield, J P; Iftimie, Radu; Salahub, Dennis; Schofield, Jeremy
2003-01-01
In this article, we propose an efficient method for sampling the relevant state space in condensed phase reactions. In the present method, the reaction is described by solving the electronic Schr\\"{o}dinger equation for the solute atoms in the presence of explicit solvent molecules. The sampling algorithm uses a molecular mechanics guiding potential in combination with simulated tempering ideas and allows thorough exploration of the solvent state space in the context of an ab initio calculation even when the dielectric relaxation time of the solvent is long. The method is applied to the study of the double proton transfer reaction that takes place between a molecule of acetic acid and a molecule of methanol in tetrahydrofuran. It is demonstrated that calculations of rates of chemical transformations occurring in solvents of medium polarity can be performed with an increase in the cpu time of factors ranging from 4 to 15 with respect to gas-phase calculations.
Ab initio study of Ni2MnGa under shear deformation
Directory of Open Access Journals (Sweden)
Zelený Martin
2015-01-01
Full Text Available The effect of shear deformation on Ni2MnGa magnetic shape memory alloy has been investigated using ab initio electronic structure calculations. We used the projector-augmented wave method for the calculations of total energies and stresses as functions of applied affine shear deformation. The studied nonmodulated martensite (NM phase exhibits a tetragonally distorted L21 structure with c/a > 1. A large strain corresponding to simple shears in {001}, {100} and {100} systems was applied to describe a full path between two equivalent NM lattices. We also studied {101} shear which is related to twining of NM phase. Twin reorientation in this system is possible, because applied positive shear results in path with significantly smaller energetic barrier than for negative shear and for shears in other studied systems. When the full relaxation of lattice parameters is allowed, the barriers further strongly decrease and the structures along the twinning path can be considered as orthorhombic.
Rosenow, Phil
2016-01-01
The extent of hydrogen coverage of the Si(001)c(4x2) surface in the presence of hydrogen gas has been studied with dispersion corrected density functional theory. Electronic energy contributions are well described using a hybrid functional. The temperature dependence of the coverage in thermodynamic equilibrium was studied computing the phonon spectrum in a supercell approach. As an approximation to these demanding computations, an interpolated phonon approach was found to give comparable accuracy. The simpler ab initio thermodynamic approach is not accurate enough for the system studied, even if corrections by the Einstein model for surface vibrations are considered. The on-set of H2 desorption from the fully hydrogenated surface is predicted to occur at temperatures around 750 K. Strong changes in hydrogen coverage are found between 1000 and 1200 K in good agreement with previous reflectance anisotropy spectroscopy experiments. These findings allow a rational choice for the surface state in the computationa...
Ab initio study of the phononic origin of negative thermal expansion
Argaman, Uri; Eidelstein, Eitan; Levy, Ohad; Makov, Guy
2016-11-01
Negative thermal expansion is an uncommon phenomenon of theoretical interest. Multiple hypotheses regarding its microscopic origins have been suggested. In this paper, the thermal expansion of a representative semiconductor, Si, and a representative metal, Ti, are calculated ab initio using density-functional perturbation theory. The phonon modes' contributions to the thermal expansion are analyzed and the negative thermal expansion is shown to be dominated by negative mode Grüneisen parameters at specific points on the Brillouin zone boundaries. Thus, the elastic (Debye) theory for negative thermal expansion is shown to be irrelevant for these phenomena. The anomalous behavior of these modes in Ti is shown to be unaffected by an electronic topological transition as previously suggested, instead it arises from complex interplay of atomic displacements of the anomalous mode.
Ab initio STUDIES ON MAGNETISM OF 3d TRANSITION METAL DIMERS
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Ab initio calculations with the self-consistent full-potential linearized augmented-plane-wave method (FLAPW), under generalized gradient approximation, have been carried out to describe the electronic and magnetic properties of 3d transition metal dimers. It predicted the antiferromagneticity of Cr2 and ferromagneticity of other species. The Mn2 dimer was shown to be ferromagnetic coupling with a local magnetic moment of 5μB. Retaining the value of its free atom state. The V2 and Ni2 exhibited low spin-polarization with local magnetic moment of only 1μB per atom. On the other hand, Fe2 and Co2 were highly spin-polarized with local magnetic moments of 3 and 2μB.
Ab Initio Calculations of Deuterium Isotope Effects on Chemical Shifts of Salt-Bridged Lysines
DEFF Research Database (Denmark)
Ullah, Saif; Ishimoto, Takayoshi; Williamson, Mike P.;
2011-01-01
Deuterium isotope effects measure the change in chemical shift on substitution of a proton by deuterium. They have been calculated by direct treatment of the H/D nuclear quantum effect using a multicomponent ab initio molecular orbital method based on a non-Born−Oppenheimer approximation....... This method enables the determination of both the electronic and the protonic (deuteronic) wave functions simultaneously and can directly calculate the geometrical difference induced by H/D isotope effects. The calculations show that the one-bond deuterium isotope effects on 15N nuclear shielding, 1Δ15N......(D), in ammonium and amines decrease as a counterion or water molecule moves closer to the nitrogen. 1Δ15N(D) and 2Δ1H(D) of the NH3+ groups of lysine residues in the B1 domain of protein G have been calculated using truncated side chains and also determined experimentally by NMR. Comparisons show...
Convergence from cluster to surface:ab initio calculations of Pd_n clusters
Institute of Scientific and Technical Information of China (English)
徐昕; 王南钦; 吕鑫; 陈明旦; 张乾二
1995-01-01
The"Metallic State Principle"and a way to constitute the metallic basis set are proposed,the latter is a modification of atomic basis set based on the free electron theory in solid state physics.Pd_n dusters have been carefully studied by means of ab initio calculations with atomic and metallic basis sets.Three rules,namely the"Ground State Principle",the"Lowest-Spin State Principle"and the"Metallic StatePrinciple"have been investigated and the calculation results based on these three rules are compared with eachother in terms of metallic configuration of bulk Pd,d-band width,Fermi level,etc.The calculation resultsdemonstrate that the characteristic properties of bulk Pd may be reproduced to some extent even with a smallduster if the"Metallic State Principle"is adopted.
Mundy, Christopher J; Curioni, Alessandro; Goldman, Nir; Will Kuo, I-F; Reed, Evan J; Fried, Laurence E; Ianuzzi, Marcella
2008-05-14
We report herein ab initio molecular dynamics simulations of graphite under shock compression in conjunction with the multiscale shock technique. Our simulations reveal that a novel short-lived layered diamond intermediate is formed within a few hundred of femtoseconds upon shock loading at a shock velocity of 12 kms (longitudinal stress>130 GPa), followed by formation of cubic diamond. The layered diamond state differs from the experimentally observed hexagonal diamond intermediate found at lower pressures and previous hydrostatic calculations in that a rapid buckling of the graphitic planes produces a mixture of hexagonal and cubic diamond (layered diamond). Direct calculation of the x-ray absorption spectra in our simulations reveals that the electronic structure of the final state closely resembles that of compressed cubic diamond.
A set of molecular models based on quantum mechanical ab initio calculations and thermodynamic data
Eckl, Bernhard; Hasse, Hans
2009-01-01
A parameterization strategy for molecular models on the basis of force fields is proposed, which allows a rapid development of models for small molecules by using results from quantum mechanical (QM) ab initio calculations and thermodynamic data. The geometry of the molecular models is specified according to the atom positions determined by QM energy minimization. The electrostatic interactions are modeled by reducing the electron density distribution to point dipoles and point quadrupoles located in the center of mass of the molecules. Dispersive and repulsive interactions are described by Lennard-Jones sites, for which the parameters are iteratively optimized to experimental vapor-liquid equilibrium (VLE) data, i.e. vapor pressure, saturated liquid density, and enthalpy of vaporization of the considered substance. The proposed modeling strategy was applied to a sample set of ten molecules from different substance classes. New molecular models are presented for iso-butane, cyclohexane, formaldehyde, dimethyl...
Ab initio study of transport properties in defected carbon nanotubes: an O(N) approach
Energy Technology Data Exchange (ETDEWEB)
Biel, Blanca; GarcIa-Vidal, F J; Flores, Fernando [Departamento de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Rubio, Angel [European Theoretical Spectroscopy Facility (ETSF), Departamento de Fisica de Materiales, Universidad PaIs Vasco, Edificio Korta, Avenida Tolosa 72, 20018 San Sebastian (Spain)], E-mail: blanca.biel@cea.fr
2008-07-23
A combination of ab initio simulations and linear-scaling Green's functions techniques is used to analyze the transport properties of long (up to 1 {mu}m) carbon nanotubes with realistic disorder. The energetics and the influence of single defects (monovacancies and divacancies) on the electronic and transport properties of single-walled armchair carbon nanotubes are analyzed as a function of the tube diameter by means of the local orbital first-principles Fireball code. Efficient O(N) Green's functions techniques framed within the Landauer-Buettiker formalism allow a statistical study of the nanotube conductance averaged over a large sample of defected tubes and thus extraction of the nanotube localization length. The cases of zero and room temperature are both addressed.
Directory of Open Access Journals (Sweden)
Karl-Heinz Böhm
2014-04-01
Full Text Available We present ab-initio calculations of secondary isotope effects on NMR chemical shieldings. The change of the NMR chemical shift of a certain nucleus that is observed if another nucleus is replaced by a different isotope can be calculated by computing vibrational corrections on the NMR parameters using electronic structure methods. We demonstrate that the accuracy of the computational results is sufficient to even distinguish different conformers. For this purpose, benchmark calculations for fluoro(2-2Hethane in gauche and antiperiplanar conformation are carried out at the HF, MP2 and CCSD(T level of theory using basis sets ranging from double- to quadruple-zeta quality. The methodology is applied to the secondary isotope shifts for 2-fluoronorbornane in order to resolve an ambiguity in the literature on the assignment of endo- and exo-2-fluoronorbornanes with deuterium substituents in endo-3 and exo-3 positions, also yielding insight into mechanistic details of the corresponding synthesis.
An ab initio potential energy surface and vibrational energy levels of HXeBr
Institute of Scientific and Technical Information of China (English)
Zheng Guo Huang; En Cui Yang; Dai Qian Xie
2008-01-01
A three-dimensional global potential energy surface for the electronic ground state of HXeBr molecule is constructed from morethan 4200 ab initio points. These points are generated using an internally contracted multi-reference configuration interactionmethod with the Davidson correction (icMRCI + Q) and large basis sets. The stabilities and dissociation barriers are identified fromthe potential energy surfaces. The three-body dissociation channel is found to be the dominate dissociation channel for HXeBr.Based on the obtained potentials, low-lying vibrational energy levels of HXeBr calculated using the Lanczos algorithm is found tobe in good agreement with the available experimental band origins.2008 Zheng Guo Huang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Ab initio theory for current-induced molecular switching: Melamine on Cu(001)
Ohto, Tatsuhiko
2013-05-28
Melamine on Cu(001) is mechanically unstable under the current of a scanning tunneling microscope tip and can switch among configurations. However, these are not equally accessible, and the switching critical current depends on the bias polarity. In order to explain such rich phenomenology, we have developed a scheme to evaluate the evolution of the reaction paths and activation barriers as a function of bias, which is rooted in the nonequilibrium Green\\'s function method implemented within density functional theory. This, combined with the calculation of the inelastic electron tunneling spectroscopy signal, allows us to identify the vibrational modes promoting the observed molecular conformational changes. Finally, once our ab initio results are used within a resonance model, we are able to explain the details of the switching behavior, such as its dependence on the bias polarity, and the noninteger power relation between the reaction rate constants and both the bias voltage and the electric current. © 2013 American Physical Society.
Yoo, Dong Su; Chae, Kisung; Chung, Yong-Chae
2012-04-01
Ab initio calculations were performed on a fully epitaxial bcc Co (001)/rock salt MgO (001)/bcc Co (001) magnetic tunnel junction system for two cases where the magnetization is parallel to bcc Co [100] and to bcc Co [110]. Structural optimization reveals that the two cases are equivalent systems and that the Co electrodes contract in the z-direction whereas the MgO insulating barrier expands. The magnetic moments of each monolayer vary slightly in each case; furthermore, only the magnetic moment at the surface of the Co atom shows any enhancement (12%). The layer decomposed density of states profiles reveals that the bonding character of the junction interface is derived mainly from the 2p-3d hybridization of the MgO and Co interfacial atoms.
Energy Technology Data Exchange (ETDEWEB)
Śmiałek, M. A., E-mail: smialek@pg.gda.pl [Department of Control and Energy Engineering, Faculty of Ocean Engineering and Ship Technology, Gdańsk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdańsk (Poland); Łabuda, M.; Guthmuller, J. [Department of Theoretical Physic and Quantum Information, Faculty of Applied Physics and Mathematics, Gdańsk University of Technology, Gabriela Narutowicza 11/12, 80-233 Gdańsk (Poland); Hubin-Franskin, M.-J.; Delwiche, J. [Département de Chimie, Université de Liège, Institut de Chimie-Bât. B6C, B-4000 Liège (Belgium); Duflot, D. [Laboratoire de Physique des Lasers, Atomes et Molécules (PhLAM), UMR CNRS 8523, Université Lille1 Sciences et Technologies, F-59655 Villeneuve d' Ascq Cedex (France); Mason, N. J. [Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom); Hoffmann, S. V.; Jones, N. C. [ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, Building 1520, DK-8000 Aarhus C (Denmark); Limão-Vieira, P., E-mail: plimaovieira@fct.unl.pt [Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal)
2014-09-14
The highest resolution vacuum ultraviolet photoabsorption spectrum of ethyl formate, C{sub 2}H{sub 5}OCHO, yet reported is presented over the wavelength range 115.0–275.5 nm (10.75–4.5 eV) revealing several new spectral features. Valence and Rydberg transitions and their associated vibronic series, observed in the photoabsorption spectrum, have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of ethyl formate and are compared with a newly recorded He(I) photoelectron spectrum (from 10.1 to 16.1 eV). New vibrational structure is observed in the first photoelectron band. The photoabsorption cross sections have been used to calculate the photolysis lifetime of ethyl formate in the upper stratosphere (20–50 km)
Energy Technology Data Exchange (ETDEWEB)
Keegan, Ronan M. [STFC Rutherford Appleton Laboratory, Didcot OX11 0FA (United Kingdom); Bibby, Jaclyn; Thomas, Jens [University of Liverpool, Liverpool L69 7ZB (United Kingdom); Xu, Dong [Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037 (United States); Zhang, Yang [University of Michigan, Ann Arbor, MI 48109 (United States); Mayans, Olga [University of Liverpool, Liverpool L69 7ZB (United Kingdom); Winn, Martyn D. [Science and Technology Facilities Council Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Rigden, Daniel J., E-mail: drigden@liv.ac.uk [University of Liverpool, Liverpool L69 7ZB (United Kingdom); STFC Rutherford Appleton Laboratory, Didcot OX11 0FA (United Kingdom)
2015-02-01
Two ab initio modelling programs solve complementary sets of targets, enhancing the success of AMPLE with small proteins. AMPLE clusters and truncates ab initio protein structure predictions, producing search models for molecular replacement. Here, an interesting degree of complementarity is shown between targets solved using the different ab initio modelling programs QUARK and ROSETTA. Search models derived from either program collectively solve almost all of the all-helical targets in the test set. Initial solutions produced by Phaser after only 5 min perform surprisingly well, improving the prospects for in situ structure solution by AMPLE during synchrotron visits. Taken together, the results show the potential for AMPLE to run more quickly and successfully solve more targets than previously suspected.
Electrical resistivity of NaPb compound-forming liquid alloy using ab initio pseudopotentials
Indian Academy of Sciences (India)
Anil Thakur; N S Negi; P K Ahluwalla
2005-08-01
The study of electrical resistivity of compound-forming liquid alloy, NaPb, is presented as a function of concentration. Hard sphere diameters of Na and Pb are obtained through the interionic pair potentials evaluated using Troullier and Martins ab initio pseudopotential, which have been used to calculate the partial structure factors (). Considering the liquid alloy to be a ternary mixture, Ziman formula, modified for complex formation has been used for calculating resistivity of binary liquid alloys. Form factors are calculated using ab initio pseudopotentials. The results suggest that Ziman formalism, when used with ab initio pseudopotentials, are quite successful in explaining the electrical resistivity data of compound-forming binary liquid alloys.
Chan, Garnet Kin-Lic; Nakatani, Naoki; Li, Zhendong; White, Steven R
2016-01-01
Current descriptions of the ab initio DMRG algorithm use two superficially different languages: an older language of the renormalization group and renormalized operators, and a more recent language of matrix product states and matrix product operators. The same algorithm can appear dramatically different when written in the two different vocabularies. In this work, we carefully describe the translation between the two languages in several contexts. First, we describe how to efficiently implement the ab-initio DMRG sweep using a matrix product operator based code, and the equivalence to the original renormalized operator implementation. Next we describe how to implement the general matrix product operator/matrix product state algebra within a pure renormalized operator-based DMRG code. Finally, we discuss two improvements of the ab initio DMRG sweep algorithm motivated by matrix product operator language: Hamiltonian compression, and a sum over operators representation that allows for perfect computational par...
Density-matrix based determination of low-energy model Hamiltonians from ab initio wavefunctions.
Changlani, Hitesh J; Zheng, Huihuo; Wagner, Lucas K
2015-09-14
We propose a way of obtaining effective low energy Hubbard-like model Hamiltonians from ab initio quantum Monte Carlo calculations for molecular and extended systems. The Hamiltonian parameters are fit to best match the ab initio two-body density matrices and energies of the ground and excited states, and thus we refer to the method as ab initio density matrix based downfolding. For benzene (a finite system), we find good agreement with experimentally available energy gaps without using any experimental inputs. For graphene, a two dimensional solid (extended system) with periodic boundary conditions, we find the effective on-site Hubbard U(∗)/t to be 1.3 ± 0.2, comparable to a recent estimate based on the constrained random phase approximation. For molecules, such parameterizations enable calculation of excited states that are usually not accessible within ground state approaches. For solids, the effective Hamiltonian enables large-scale calculations using techniques designed for lattice models.
ab initio Studies on Molecular Conductor (BEDSe-TTF)2[Fe(CN)5NO
Institute of Scientific and Technical Information of China (English)
YAO Kai-Lun; TU Hai-Bo; WANG Wei-Zhong
2001-01-01
In this paper the ab initio study using pseudopotential plane wave method with the local spin density functional approximation is presented for the molecular conductor (BEDSe-TTF)2[Fe(CN)5NO]. The mean electronic density distributions are obtained, and we find that the extended π orbital of the selenium does not affect the properties of material as assumed in other papers and the "side-by-side" type S...S interaction is the primary interaction between donors. From band structure calculations we analyze the influence of the NO groups on the electronic structure and magnetic properties of molecule. It is shown that the itinerant electrons important to electronic properties in these types of hybrids are delocalized electrons contributed by NO groups, instead of by the 3d electrons of Fe. Additionally, we have found that the localized magnetic moment is also contributed by the NO groups in this molecular conductor. From total energy calculations the molecular structure with the lowest energy is found due to the interaction between split spins, and the particular positions of the NO groups are obtained.
Energy Technology Data Exchange (ETDEWEB)
Willaime, F. [Division de l' energie nucleaire, CEA Centre de Saclay, 91191 Gif-sur-Yvette (France); Deutsch, T.; Pochet, P. [INAC, Direction des sciences de la matiere, CEA Centre de Grenoble, 38054 Grenoble Cedex 9 (France)
2010-07-01
Ab-initio calculation methods, for the purposes of computing electronic structures, have made it possible, since the early nineties, to simulate the properties of perfect crystalline materials (materials free of any defect). By improving such methods, and with the increasing power of supercomputers, it has now become feasible to simulate the properties of elementary defects, which may seldom be accessed directly through experiments. This has opened up a vast, fruitful field of multi-scale simulations, where such data yield the basis for realistic simulations of the kinetics of materials evolution. The kinetic Monte-Carlo method thus provides the means to model phenomena acting at the scale of a second, or even of a year. In the issue of self-diffusion in silicon, multi-scale simulation has been successful in predicting an asymmetrical behaviour: a speeding up of vacancy diffusion under compression and a tailing off under tension, and conversely, a speeding up of interstitial diffusion under tension and a falling off under compression. Multi-scale modeling has also been successful in simulating irradiation defects in iron. (A.C.)
Lopuszynski, Michal; Majewski, Jacek A.
2007-01-01
We present theoretical studies for the third-order elastic constants $C_{ijk}$ in zinc-blende nitrides AlN, GaN, and InN. Our predictions for these compounds are based on detailed ab initio calculations of strain-energy and strain-stress relations in the framework of the density functional theory. To judge the computational accuracy, we compare the ab initio calculated results for $C_{ijk}$ with experimental data available for Si and GaAs. We also underline the relation of the third-order ela...
Keegan, Ronan M; Bibby, Jaclyn; Thomas, Jens; Xu, Dong; Zhang, Yang; Mayans, Olga; Winn, Martyn D; Rigden, Daniel J
2015-02-01
AMPLE clusters and truncates ab initio protein structure predictions, producing search models for molecular replacement. Here, an interesting degree of complementarity is shown between targets solved using the different ab initio modelling programs QUARK and ROSETTA. Search models derived from either program collectively solve almost all of the all-helical targets in the test set. Initial solutions produced by Phaser after only 5 min perform surprisingly well, improving the prospects for in situ structure solution by AMPLE during synchrotron visits. Taken together, the results show the potential for AMPLE to run more quickly and successfully solve more targets than previously suspected.
Energy Technology Data Exchange (ETDEWEB)
Ganster, P
2004-10-15
A calcium aluminosilicate glass of molar composition 67 % SiO{sub 2} - 12 % Al{sub 2}O{sub 3} - 21 % CaO was modelled by classical and ab initio molecular dynamics. The size effect study in classical MD shows that the systems of 100 atoms are more ordered than the larger ones. These effects are mainly due to the 3-body terms in the empirical potentials. Nevertheless, these effects are small and the structures generated are in agreement with experimental data. In such kind of glass, we denote an aluminium avoidance and an excess of non bridging oxygens which can be compensated by tri coordinated oxygens. When the dynamics of systems of 100 and 200 atoms is followed by ab initio MD, some local arrangements occurs (bond length, angular distributions). Thus, more realistic vibrational properties are obtained in ab initio MD. The modelling of thin films shows that aluminium atoms extend to the most external part of the surface and they are all tri-coordinated. Calcium atoms are set in the sub layer part of the surface and they produce a depolymerization of the network. In classical MD, tri-coordinated aluminium atoms produce an important electric field above the surface. With non bridging oxygens, they constitute attractive sites for single water molecules. (author)
High pressure behaviour of uranium dicarbide (UC2): Ab-initio study
Sahoo, B. D.; Mukherjee, D.; Joshi, K. D.; Kaushik, T. C.
2016-08-01
The structural stability of uranium dicarbide has been examined under hydrostatic compression employing evolutionary structure search algorithm implemented in the universal structure predictor: evolutionary Xtallography (USPEX) code in conjunction with ab-initio electronic band structure calculation method. The ab-initio total energy calculations involved for this purpose have been carried out within both generalized gradient approximations (GGA) and GGA + U approximations. Our calculations under GGA approximation predict the high pressure structural sequence of tetragonal → monoclinic → orthorhombic for this material with transition pressures of ˜8 GPa and 42 GPa, respectively. The same transition sequence is predicted by calculations within GGA + U also with transition pressures placed at ˜24 GPa and ˜50 GPa, respectively. Further, on the basis of comparison of zero pressure equilibrium volume and equation of state with available experimental data, we find that GGA + U approximation with U = 2.5 eV describes this material better than the simple GGA approximation. The theoretically predicted high pressure structural phase transitions are in disagreement with the only high experimental study by Dancausse et al. [J. Alloys. Compd. 191, 309 (1993)] on this compound which reports a tetragonal to hexagonal phase transition at a pressure of ˜17.6 GPa. Interestingly, during lowest enthalpy structure search using USPEX, we do not see any hexagonal phase to be closer to the predicted monoclinic phase even within 0.2 eV/f. unit. More experiments with varying carbon contents in UC2 sample are required to resolve this discrepancy. The existence of these high pressure phases predicted by static lattice calculations has been further substantiated by analyzing the elastic and lattice dynamic stability of these structures in the pressure regimes of their structural stability. Additionally, various thermo-physical quantities such as equilibrium volume, bulk modulus, Debye
The keto-enol equilibrium in substituted acetaldehydes: focal-point analysis and ab initio limit
Balabin, Roman M.
2011-10-01
High-level ab initio electronic structure calculations up to the CCSD(T) theory level, including extrapolations to the complete basis set (CBS) limit, resulted in high precision energetics of the tautomeric equilibrium in 2-substituted acetaldehydes (XH2C-CHO). The CCSD(T)/CBS relative energies of the tautomers were estimated using CCSD(T)/aug-cc-pVTZ, MP3/aug-cc-pVQZ, and MP2/aug-cc-pV5Z calculations with MP2/aug-cc-pVTZ geometries. The relative enol (XHC = CHOH) stabilities (ΔE e,CCSD(T)/CBS) were found to be 5.98 ± 0.17, -1.67 ± 0.82, 7.64 ± 0.21, 8.39 ± 0.31, 2.82 ± 0.52, 10.27 ± 0.39, 9.12 ± 0.18, 5.47 ± 0.53, 7.50 ± 0.43, 10.12 ± 0.51, 8.49 ± 0.33, and 6.19 ± 0.18 kcal mol-1 for X = BeH, BH2, CH3, Cl, CN, F, H, NC, NH2, OCH3, OH, and SH, respectively. Inconsistencies between the results of complex/composite energy computations methods Gn/CBS (G2, G3, CBS-4M, and CBS-QB3) and high-level ab initio methods (CCSD(T)/CBS and MP2/CBS) were found. DFT/aug-cc-pVTZ results with B3LYP, PBE0 (PBE1PBE), TPSS, and BMK density functionals were close to the CCSD(T)/CBS levels (MAD = 1.04 kcal mol-1).
Benassi, R.; Bertarini, C.; Hilfert, L.; Kempter, G.; Kleinpeter, E.; Spindler, J.; Taddei, F.; Thomas, S.
2000-03-01
The structure of a number of 2- exo-methylene substituted quinazolines and benzodiazepines, respectively, 1, 3a, b, 4( X=-CN, -COOEt ) and their 2-cyanoimino substituted analogues 2, 3c, d( X=-CN, -SO 2C 6H 4-Me (p) was completely assigned by the whole arsenal of 1D and 2D NMR spectroscopic methods. The E/ Z isomerism at the exo-cyclic double bond was determined by both NMR spectroscopy and confirmed by ab initio quantum chemical calculations; the Z isomer is the preferred one, its amount proved dependent on steric hindrance. Due to the push-pull effect in this part of the molecules the restricted rotation about the partial C 2,C 11 and C 2,N 11 double bonds, could also be studied and the barrier to rotation measured by dynamic NMR spectroscopy. The free energies of activation of this dynamic process proved very similar along the compounds studied but being dependent on the polarity of the solvent. Quantum chemical calculations at the ab initio level were employed to prove the stereochemistry at the exo-cyclic partial double bonds of 1- 4, to calculate the barriers to rotation but also to discuss in detail both the ground and the transition state of the latter dynamic process in order to better understand electronic, inter- and intramolecular effects on the barrier to rotation which could be determined experimentally. In the cyanoimino substituted compounds 2, 3c, d, the MO ab initio calculations evidence the isomer interconversion to be better described by the internal rotation process than by the lateral shift mechanism.
Kakizaki, Akira; Takayanagi, Toshiyuki; Shiga, Motoyuki
2007-11-01
Path integral molecular dynamics simulations for the H6+ and D6+ cluster cations have been carried out in order to understand the floppy nature of their molecular structure due to quantum-mechanical fluctuation. A full-dimensional analytical potential energy surface for the ground electronic state of H6+ has been developed on the basis of accurate ab initio electronic structure calculations at the CCSD(T)/cc-pVTZ level. It is found that the outer H 2(D 2) nuclei rotate almost freely and that the probability density distributions of the central H 2(D 2) nuclei show strong spatial delocalization.
Study on the effects of fluorine and oxygen deficiency on YBa2Cu3O7 by ab initio method
Institute of Scientific and Technical Information of China (English)
刘洪霖; 曹晓卫; 瞿丽曼; 陈念贻
1997-01-01
The calculations of clusters modeling the fluorine-doping and oxygen deficiency of YBa2Cu3O2,have been performed by the method of all-electron ab initio Hartree-Fock with self-consistent crystal field Results show that in CuO planes electric charge significantly increases,the chemical valence of Cu decreases and the covalent bonding of Cu-O greatly weakens owing to oxygen deficiency,while the effect of F restores the local electronic structure of YBa2Cu3O7 The reported opinion that F occupied the oxygen vacancy in Cu-O chains seems disputable according to the calculated bonding characteristics.
Linker, Gerrit-Jan; van Loosdrecht, Paul H. M.; van Duijnen, Piet; Broer, Ria
2010-01-01
We performed ab initio quantum chemical calculations for the geometrical and electronic structure of the EDO-TTF (ethylenedioxy-tetrathiafulvalene) molecule using HF, CASSCF and DFT methods. We compare these in vacuo results with the properties of the (EDO-TTF)(2)PF6 crystal at near room temperature
Switchable magnetic moment in cobalt-doped graphene bilayer on Cu(111): An ab initio study
Souza, Everson S.; Scopel, Wanderlã L.; Miwa, R. H.
2016-06-01
In this work, we have performed an ab initio theoretical investigation of substitutional cobalt atoms in the graphene bilayer supported on the Cu(111) surface (Co/GBL/Cu). Initially, we examined the separated systems, namely, graphene bilayer adsorbed on Cu(111) (GBL/Cu) and a free standing Co-doped GBL (Co/GBL). In the former system, the GBL becomes n -type doped, where we map the net electronic charge density distribution along the GBL-Cu(111) interface. The substitutional Co atom in Co/GBL lies between the graphene layers, and present a net magnetic moment mostly due to the unpaired Co-3 dz2 electrons. In Co/GBL/Cu, we found that the Cu(111) substrate rules (i) the energetic stability, and (ii) the magnetic properties of substitutional Co atoms in the graphene bilayer. In (i), the substitutional Co atom becomes energetically more stable lying on the GBL surface, and in (ii), the magnetic moment of Co/GBL has been quenched due to the Cu(111) → Co/GBL electronic charge transfer. We verify that such a charge transfer can be tuned upon the application of an external electric field, and thus mediated by a suitable change on the electronic occupation of the Co-dz2 orbitals, we found a way to switch-on and -off the magnetization of the Co-doped GBL adsorbed on the Cu(111) surface.
Ab initio random structure search for 13-atom clusters of fcc elements.
Chou, J P; Hsing, C R; Wei, C M; Cheng, C; Chang, C M
2013-03-27
The 13-atom metal clusters of fcc elements (Al, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au) were studied by density functional theory calculations. The global minima were searched for by the ab initio random structure searching method. In addition to some new lowest-energy structures for Pd13 and Au13, we found that the effective coordination numbers of the lowest-energy clusters would increase with the ratio of the dimer-to-bulk bond length. This correlation, together with the electronic structures of the lowest-energy clusters, divides the 13-atom clusters of these fcc elements into two groups (except for Au13, which prefers a two-dimensional structure due to the relativistic effect). Compact-like clusters that are composed exclusively of triangular motifs are preferred for elements without d-electrons (Al) or with (nearly) filled d-band electrons (Ni, Pd, Cu, Ag). Non-compact clusters composed mainly of square motifs connected by some triangular motifs (Rh, Ir, Pt) are favored for elements with unfilled d-band electrons.
Energy Technology Data Exchange (ETDEWEB)
Alipour, Mojtaba, E-mail: malipour@shirazu.ac.ir [Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of); Mohajeri, Afshan, E-mail: amohajeri@shirazu.ac.ir [Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of)
2011-08-25
Graphical abstract: The electronic properties such as the static dipole polarizability, anisotropy of the polarizability, and dipole moment of yttrium bromide, YBr (X{sup 1}{Sigma}) have been theoretically studied. Highlights: {yields} Conventional ab initio and density functional theory methods were employed to study linear optical properties of YBr molecule. {yields} Properties derivatives and their level of theory dependence were studied. {yields} Electron correlation effects and rovibrational corrections have also been discussed. - Abstract: We have employed conventional ab initio and density functional theory methods to study the electronic properties such as the mean static dipole polarizability, {alpha}-bar, anisotropy of the polarizability, {Delta}{alpha}, and dipole moment, {mu}, of yttrium bromide. The bond length dependence of properties is determined at different levels of theory and appropriate expansions around experimental internuclear distance have been presented. Moreover, the first and second geometrical derivatives for each property are quantified and their level of theory dependence has been analyzed. To study the effect of molecular rotation and vibration on the electronic properties, the rovibrational corrections have also been carried out. It is found that these corrections are less pronounced for considered properties of YBr. In all calculations, the electron correlation effects have been considered and discussed. The obtained results show that the electron correlation is more significant in the calculation of the mean and the anisotropy of dipole polarizability.
Raman and ab initio studies of simple and binary 1-alkyl-3-methylimidazolium ionic liquids
DEFF Research Database (Denmark)
Berg, R.W.; Deetlefs, M.; Seddon, K.R.;
2005-01-01
Raman spectra of the ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim][PF6]), 1-hexyl-3-methylimidazolium chloride ([C(6)mim]Cl), and 1-hexyl-3-methylimidazolium hexafluorophosphate ([C(6)mim][PF6]), and binary mixtures thereof, have been assigned using ab initio MP2...
Ab initio study of energy-level alignments in polymer-dye blends
Pasveer, W.F.; Bobbert, P.A.; Michels, M.A.J.; Langeveld-Voss, B.M.W.; Schoo, H.F.M.; Bastiaansen, J.J.A.M.
2003-01-01
Polymers with a small amount of dye blended in offer an attractive possibility to change the color of the emitted light by changing the dye. We present ab initio calculations within density-functional theory of the HOMO/ LUMO energies for dipyrrolomethane dyes, polyphenylenevinylene and polyfluorene
Ab initio study of long-period superstructures in close-packed A3B compounds
DEFF Research Database (Denmark)
Rosengaard, N. M.; Skriver, Hans Lomholt
1994-01-01
We have performed ab initio calculations of the stability of one-dimensional long-period superstructures in Cu3Pd, Cu3Al, and Ag3Mg by means of an interface Green's function technique based on the linear-muffin-tin-orbitals method within the tight-binding and atomic-sphere approximations. The ene...
Mechanical properties of carbynes investigated by ab initio total-energy calculations
DEFF Research Database (Denmark)
Castelli, Ivano E.; Salvestrini, Paolo; Manini, Nicola
2012-01-01
As sp carbon chains (carbynes) are relatively rigid molecular objects, can we exploit them as construction elements in nanomechanics? To answer this question, we investigate their remarkable mechanical properties by ab initio total-energy simulations. In particular, we evaluate their linear...... response to small longitudinal and bending deformations and their failure limits for longitudinal compression and elongation....
Ab initio Defect Energetics in LaBO3 Perovskite Solid Oxide Fuel Cell Materials
DEFF Research Database (Denmark)
Lee, Yueh-Lin; Morgan, Dane; Kleis, Jesper;
2009-01-01
Perovskite materials of the form ABO3 are a promising family of compounds for use in solid oxide fuel cell (SOFC) cathodes. Study of the physics of these compounds under SOFC conditions with ab initio methods is particularly challenging due to high temperatures, exchange of oxygen with O2 gas...
Ab-initio modeling of an anion $C_{60}^-$ pseudopotential for fullerene-based compounds
Vrubel, I I; Ivanov, V K
2015-01-01
A pseudopotential of $C_{60}^-$ has been constructed from ab-initio quantum-mechanical calculations. Since the obtained pseudopotential can be easily fitted by rather simple analytical approximation it can be effectively used both in classical and quantum molecular dynamics of fullerene-based compounds.
An ab initio Valence Bond Study on Cyclopenta-Fused Naphthalenes and Fluoranthenes
Havenith, R.W.A.; van Lenthe, J.H.; Jenneskens, L.W.
2005-01-01
To probe the effect of external cyclopenta-fusion on a naphthalene core, ab initio valence bond (VB) calculations have been performed, using strictly atomic benzene p-orbitals and p-orbitals that are allowed to delocalize, on naphthalene (1), acenaphthylene (2), pyracylene (3), cyclopenta[b,c]-acena
Computer simulation of acetonitrile and methanol with ab initio-based pair potentials
Hloucha, M.; Sum, A. K.; Sandler, S. I.
2000-10-01
This study address the adequacy of ab initio pair interaction energy potentials for the prediction of macroscopic properties. Recently, Bukowski et al. [J. Phys. Chem. A 103, 7322 (1999)] performed a comprehensive study of the potential energy surfaces for several pairs of molecules using symmetry-adapted perturbation theory. These ab initio energies were then fit to an appropriate site-site potential form. In an attempt to bridge the gap between ab initio interaction energy information and macroscopic properties prediction, we performed Gibbs ensemble Monte Carlo (GEMC) simulations using their developed pair potentials for acetonitrile and methanol. The simulations results show that the phase behavior of acetonitrile is well described by just the pair interaction potential. For methanol, on the other hand, pair interactions are insufficient to properly predict its vapor-liquid phase behavior, and its saturated liquid density. We also explored simplified forms for representing the ab initio interaction energies by refitting a selected range of the data to a site-site Lennard-Jones and to a modified Buckingham (exponential-6) potentials plus Coulombic interactions. These were also used in GEMC simulations in order to evaluate the quality and computational efficiency of these different potential forms. It was found that the phase behavior prediction for acetonitrile and methanol are highly dependent on the details of the interaction potentials developed.
DEFF Research Database (Denmark)
Cybulski, Hubert; Fernandez, Berta; Henriksen, Christian
2012-01-01
We evaluate the phenylacetylene-argon intermolecular potential energy surface by fitting a representative number of ab initio interaction energies to an analytic function. These energies are calculated at a grid of intermolecular geometries, using the CCSD(T) method and the aug-cc-pVDZ basis set ...
Ab Initio Investigations of the C2F4S Isomers and of Their Interconversions
DEFF Research Database (Denmark)
Shim, Irene; Vallano-Lorenzo, Sandra; Lisbona-Martin, Pilar
2003-01-01
The transition states and the activation energies for the unobserved isomerization reactions between the three possible C2F4S isomers with divalent sulfur, trifluorothioacetyl fluoride 1, tetrafluorothiirane 2, and trifluoroethenesulfenyl fluoride 3, have been determined by ab initio Hartree-Fock...
Ab initio calculations on the structure of pyridine in its lowest triplet state
Buma, W.J.; Groenen, E.J.J.; Schmidt, J.
1990-01-01
Recently we have experimentally shown that pyridine-d5, as a guest in a single crystal of benzene-d6, adopts a boatlike structure upon excitation into the lowest triplet state T0. Here MRDCI ab initio calculations are presented that reveal that the observed nonplanarity of the molecule is not caused
Chan, Garnet Kin-Lic; Keselman, Anna; Nakatani, Naoki; Li, Zhendong; White, Steven R.
2016-07-01
Current descriptions of the ab initio density matrix renormalization group (DMRG) algorithm use two superficially different languages: an older language of the renormalization group and renormalized operators, and a more recent language of matrix product states and matrix product operators. The same algorithm can appear dramatically different when written in the two different vocabularies. In this work, we carefully describe the translation between the two languages in several contexts. First, we describe how to efficiently implement the ab initio DMRG sweep using a matrix product operator based code, and the equivalence to the original renormalized operator implementation. Next we describe how to implement the general matrix product operator/matrix product state algebra within a pure renormalized operator-based DMRG code. Finally, we discuss two improvements of the ab initio DMRG sweep algorithm motivated by matrix product operator language: Hamiltonian compression, and a sum over operators representation that allows for perfect computational parallelism. The connections and correspondences described here serve to link the future developments with the past and are important in the efficient implementation of continuing advances in ab initio DMRG and related algorithms.
Ab initio calculations on the inclusion complexation of cyclobis(paraquat- p-phenylene)
Zhang, Ke-Chun; Liu, Lei; Mu, Ting-Wei; Guo, Qing-Xiang
2001-01-01
Semiempirical PM3, ab initio HF/3-21g ∗, and DFT B3LYP/6-31g ∗ calculations in vacuum and in solution were performed on the inclusion complexation of cyclobis(paraquat- p-phenylene) with nine symmetric aromatic substrates. A good correlation was found between the theoretical stabilization energies and experimental free energy changes upon complexation.
Chan, Garnet Kin-Lic; Keselman, Anna; Nakatani, Naoki; Li, Zhendong; White, Steven R
2016-07-01
Current descriptions of the ab initio density matrix renormalization group (DMRG) algorithm use two superficially different languages: an older language of the renormalization group and renormalized operators, and a more recent language of matrix product states and matrix product operators. The same algorithm can appear dramatically different when written in the two different vocabularies. In this work, we carefully describe the translation between the two languages in several contexts. First, we describe how to efficiently implement the ab initio DMRG sweep using a matrix product operator based code, and the equivalence to the original renormalized operator implementation. Next we describe how to implement the general matrix product operator/matrix product state algebra within a pure renormalized operator-based DMRG code. Finally, we discuss two improvements of the ab initio DMRG sweep algorithm motivated by matrix product operator language: Hamiltonian compression, and a sum over operators representation that allows for perfect computational parallelism. The connections and correspondences described here serve to link the future developments with the past and are important in the efficient implementation of continuing advances in ab initio DMRG and related algorithms.
DEFF Research Database (Denmark)
Abild-Pedersen, Frank; Nørskov, Jens Kehlet; Rostrup-Nielsen, Jens;
2006-01-01
Mechanisms and energetics of graphene growth catalyzed by nickel nanoclusters were studied using ab initio density functional theory calculations. It is demonstrated that nickel step-edge sites act as the preferential growth centers for graphene layers on the nickel surface. Carbon is transported...
New ab initio based pair potential for accurate simulation of phase transitions in ZnO
Wang, Shuaiwei; Fan, Zhaochuan; Koster, Rik S.; Fang, Changming; Van Huis, Marijn A.; Yalcin, Anil O.; Tichelaar, Frans D.; Zandbergen, Henny W.; Vlugt, Thijs J H
2014-01-01
A set of interatomic pair potentials is developed for ZnO based on the partially charged rigid ion model (PCRIM). The derivation of the potentials combines lattice inversion, empirical fitting, and ab initio energy surface fitting. We show that, despite the low number of parameters in this model (8)
Ab Initio Calculations and Raman and SERS Spectral Analyses of Amphetamine Species
DEFF Research Database (Denmark)
Berg, Rolf W.; Nørbygaard, Thomas; White, Peter C.
2011-01-01
. The spectra of amphetamine and amphetamine-H+ sampleswere obtained and assigned according to a comparison of the experimental spectra and the ab initio MO calculations, performed using the Gaussian 03W program (Gaussian, Inc., Pittsburgh, PA). The analyses were based on complete geometry minimization...
Periodic Trends in Lanthanide Compounds through the Eyes of Multireference ab Initio Theory.
Aravena, Daniel; Atanasov, Mihail; Neese, Frank
2016-05-01
Regularities among electronic configurations for common oxidation states in lanthanide complexes and the low involvement of f orbitals in bonding result in the appearance of several periodic trends along the lanthanide series. These trends can be observed on relatively different properties, such as bonding distances or ionization potentials. Well-known concepts like the lanthanide contraction, the double-double (tetrad) effect, and the similar chemistry along the lanthanide series stem from these regularities. Periodic trends on structural and spectroscopic properties are examined through complete active space self-consistent field (CASSCF) followed by second-order N-electron valence perturbation theory (NEVPT2) including both scalar relativistic and spin-orbit coupling effects. Energies and wave functions from electronic structure calculations are further analyzed in terms of ab initio ligand field theory (AILFT), which allows one to rigorously extract angular overlap model ligand field, Racah, and spin-orbit coupling parameters directly from high-level ab initio calculations. We investigated the elpasolite Cs2NaLn(III)Cl6 (Ln(III) = Ce-Nd, Sm-Eu, Tb-Yb) crystals because these compounds have been synthesized for most Ln(III) ions. Cs2NaLn(III)Cl6 elpasolites have been also thoroughly characterized with respect to their spectroscopic properties, providing an exceptionally vast and systematic experimental database allowing one to analyze the periodic trends across the lanthanide series. Particular attention was devoted to the apparent discrepancy in metal-ligand covalency trends between theory and spectroscopy described in the literature. Consistent with earlier studies, natural population analysis indicates an increase in covalency along the series, while a decrease in both the nephelauxetic (Racah) and relativistic nephelauxetic (spin-orbit coupling) reduction with increasing atomic number is calculated. These apparently conflicting results are discussed on the
Timko, Jeff; Kuyucak, Serdar
2012-11-28
Polarization is an important component of molecular interactions and is expected to play a particularly significant role in inhomogeneous environments such as pores and interfaces. Here we investigate the effects of polarization in the gramicidin A ion channel by performing quantum mechanics/molecular mechanics molecular dynamics (MD) simulations and comparing the results with those obtained from classical MD simulations with non-polarizable force fields. We consider the dipole moments of backbone carbonyl groups and channel water molecules as well as a number of structural quantities of interest. The ab initio results show that the dipole moments of the carbonyl groups and water molecules are highly sensitive to the hydrogen bonds (H-bonds) they participate in. In the absence of a K(+) ion, water molecules in the channel are quite mobile, making the H-bond network highly dynamic. A central K(+) ion acts as an anchor for the channel waters, stabilizing the H-bond network and thereby increasing their average dipole moments. In contrast, the K(+) ion has little effect on the dipole moments of the neighboring carbonyl groups. The weakness of the ion-peptide interactions helps to explain the near diffusion-rate conductance of K(+) ions through the channel. We also address the sampling issue in relatively short ab initio MD simulations. Results obtained from a continuous 20 ps ab initio MD simulation are compared with those generated by sampling ten windows from a much longer classical MD simulation and running each window for 2 ps with ab initio MD. Both methods yield similar results for a number of quantities of interest, indicating that fluctuations are fast enough to justify the short ab initio MD simulations.
Systematic ab initio study of half-Heusler materials for optoelectronic applications
Energy Technology Data Exchange (ETDEWEB)
Gruhn, Thomas; Felser, Claudia [Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg University, Mainz (Germany)
2010-07-01
The development of new, optimized optoelectronic devices depends crucially on the availability of semiconductors with taylored electronic and structural properties. At the moment, the majority of applications is based on a rather small set of semiconducting materials, while many more semiconductors exist in the huge class of ternary compounds. Especially, the class of 8-electron half-Heusler materials comprises a large number semiconducters with various properties. With the help of ab initio density functional theory we have studied essentially all 8-electron half-Heusler compounds that are of technological relevance. For more than 650 compounds we have determined the optimum configuration by varying the lattice constant and permuting the elements over the sublattices. Within this exceptionally large data set we have studied the band structure and the lattice constants as a function of the electronegativities of the elements, the arrangement of the atoms, and the atomic radii. The results are used to select suitable materials for the buffer layer in thin-film solar cells with a Cu(In,Ga)Se{sub 2} (CIGS) absorber layer. Considering the bandgap and the geometrical matching with the CIGS film, we have obtained a set of 29 compounds that are promissing materials for cadmium-free CIGS buffer layer.
Ab initio theory of exchange interactions and the Curie temperature of bulk Gd
Turek, I; Bihlmayer, G; Bluegel, S
2003-01-01
An ab initio approach to the magnetic properties of bulk hexagonal Gd is developed that is based on the local spin-density approximation with the 4f electrons treated as localized core electrons. The effective one-electron problem is solved using the tight-binding linear muffin-tin orbital method in the atomic-sphere approximation with the valence basis consisting of s-, p-and d-type orbitals. The approach leads to a correct description of the ground-state properties like the stability of the ferromagnetic structure, the magnetic moment and the equilibrium lattice constant. Application of a real-space Green-function formalism yields the exchange pair interactions between distant neighbours that are inevitable for quantitative studies of magnetic excitations. The distance dependence and anisotropy of the exchange pair interactions are presented and the Curie temperature in the mean-field approximation is evaluated. The obtained value of 334 K is in much better agreement with the experimental value of 293 K tha...
Ab Initio Enhanced calphad Modeling of Actinide-Rich Nuclear Fuels
Energy Technology Data Exchange (ETDEWEB)
Morgan, Dane [Univ. of Wisconsin, Madison, WI (United States); Yang, Yong Austin [Univ. of Wisconsin, Madison, WI (United States)
2013-10-28
The process of fuel recycling is central to the Advanced Fuel Cycle Initiative (AFCI), where plutonium and the minor actinides (MA) Am, Np, and Cm are extracted from spent fuel and fabricated into new fuel for a fast reactor. Metallic alloys of U-Pu-Zr-MA are leading candidates for fast reactor fuels and are the current basis for fast spectrum metal fuels in a fully recycled closed fuel cycle. Safe and optimal use of these fuels will require knowledge of their multicomponent phase stability and thermodynamics (Gibbs free energies). In additional to their use as nuclear fuels, U-Pu-Zr-MA contain elements and alloy phases that pose fundamental questions about electronic structure and energetics at the forefront of modern many-body electron theory. This project will validate state-of-the-art electronic structure approaches for these alloys and use the resulting energetics to model U-Pu-Zr-MA phase stability. In order to keep the work scope practical, researchers will focus on only U-Pu-Zr-{Np,Am}, leaving Cm for later study. The overall objectives of this project are to: Provide a thermodynamic model for U-Pu-Zr-MA for improving and controlling reactor fuels; and, Develop and validate an ab initio approach for predicting actinide alloy energetics for thermodynamic modeling.
Hafner, Jürgen
2010-09-29
During the last 20 years computer simulations based on a quantum-mechanical description of the interactions between electrons and atomic nuclei have developed an increasingly important impact on materials science, not only in promoting a deeper understanding of the fundamental physical phenomena, but also enabling the computer-assisted design of materials for future technologies. The backbone of atomic-scale computational materials science is density-functional theory (DFT) which allows us to cast the intractable complexity of electron-electron interactions into the form of an effective single-particle equation determined by the exchange-correlation functional. Progress in DFT-based calculations of the properties of materials and of simulations of processes in materials depends on: (1) the development of improved exchange-correlation functionals and advanced post-DFT methods and their implementation in highly efficient computer codes, (2) the development of methods allowing us to bridge the gaps in the temperature, pressure, time and length scales between the ab initio calculations and real-world experiments and (3) the extension of the functionality of these codes, permitting us to treat additional properties and new processes. In this paper we discuss the current status of techniques for performing quantum-based simulations on materials and present some illustrative examples of applications to complex quasiperiodic alloys, cluster-support interactions in microporous acid catalysts and magnetic nanostructures.
Relaxation of Small Molecules：an ab initio Study
Institute of Scientific and Technical Information of China (English)
CAOYi－Gang; A.Antons; 等
2002-01-01
Using an ab inito total energy and force method,we have relaxed several group IV and group V elemental clusters,in detail the arsenic and antimony dimers,silicon,phosphorus,arsenic and antimony tetraners,The obtained bond lengths and cohesive energies are more accurate than other calculating methods,and in excellent agreement with the experimental results.
Sun, Hosung; Freed, Karl F.
1984-01-01
The exact ab initio effective valence shell Hamiltonian, which is mimicked by semiempirical theories of valence, is calculated for CH at 11 bond lengths using quasidegenerate many-body perturbation theory to incorporate extensive correlation contributions. Least squares fits of the bond length dependence of the calculated CH matrix elements provide simple formulas which are compared with the intuitive forms introduced into semiempirical theories. Some of the semiempirical formulas, e.g., one-center, one-electron integrals and two-center, two-electron integrals, are in good agreement with our correlated ab initio calculations, while others display substantial departures. For example, the bond length dependence of one-center, two-electron integrals, which are assumed to be independent of bond length in semiempirical theories, is substantial but physically understandable. Corrections are found to the assumed proportionality of resonance and overlap integrals. The bond length dependence of nonclassical three-electron integrals is presented along with the hybrid and exchange integrals that are ignored in zero differential overlap methods.
Zhu, L.; Yao, K. L.; Liu, Z. L.
2007-10-01
Ab initio computations within the full potential linearized augmented plane wave method with the generalized gradient approximation plus Hubbard potential approach were applied in the study of the electronic structures of the compound [Gd2(mal)3(H2O)6] . The present calculations show that the major part of the spin magnetic moment is from Gd(III) ions, and the origin of the ferromagnetic intermolecular interaction of the two interacting Gd(III) ions comes from the spin polarization effect through the oxo-carboxylato and carboxylato bridges. By analysis of the band structure, we find that the compound has a metallic property.
Energy Technology Data Exchange (ETDEWEB)
Kim, B.
1990-10-01
This report discusses the following topics: molecular structure of NO{sub 3} radical studied by laser induced fluorescence; photodissociation and fluorescence spectroscopy of NO{sub 3} in molecular beam; vertical electronic spectrum of NO{sub 3}:{sup 2}A{prime}{sub 2}, {sup 2}E{double prime}({sup 2}A{sub 2}{sup 2}B{sub 1}), and {sup 2}E{prime} states; and Ab initio study of the vibrational spectra of NO{sub 3}.
Lasoroski, Aurélie; Vuilleumier, Rodolphe; Pollet, Rodolphe
2014-07-07
The electronic relaxation of gadolinium complexes used as MRI contrast agents was studied theoretically by following the short time evolution of zero-field-splitting parameters. The statistical analysis of ab initio molecular dynamics trajectories provided a clear separation between static and transient contributions to the zero-field-splitting. For the latter, the correlation time was estimated at approximately 0.1 ps. The influence of the ligand was also probed by replacing one pendant arm of our reference macrocyclic complex by a bulkier phosphonate arm. In contrast to the transient contribution, the static zero-field-splitting was significantly influenced by this substitution.
Andrés, J. L.; Lledós, A.; Duran, M.; Bertrán, J.
1988-12-01
Ab initio SCF calculations have been carried out on the fluoride exchange reaction F -+CH 3F→FCH 3+F -. An external uniform electric field along the FCF axis has been incorporated by proper changes in the one-electron part of the Fock matrix. The reaction profile has been found to be dramatically modified with increase in strength of the applied field. The electric field is found to be essential to describe the potential energy hypersurface so that it intervenes in the reaction coordinate. It is concluded that strong electric fields open a new way to catalyze reactions.
Ab-initio study of high temperature lattice dynamics of BCC zirconium (β-Zr) and uranium (γ-U)
Energy Technology Data Exchange (ETDEWEB)
Ghosh, Partha S., E-mail: parthasarathi13@gmail.com; Arya, A., E-mail: parthasarathi13@gmail.com; Dey, G. K., E-mail: parthasarathi13@gmail.com [Materials Science Division, Bhabha Atomic Research Centre, Mumbai-400085 (India)
2014-04-24
Using self consistent ab-initio lattice dynamics calculations, we show that bcc structures of Zr and U phases become stable at high temperature by phonon-phonon interactions. The calculated temperature dependent phonon dispersion curve (PDC) of β-Zr match excellently with experimental PDC. But the calculated PDC for γ-U shows negative phonon frequencies even at solid to liquid transition temperature. We show that this discrepancy is due to an overestimation of instability depth of bcc U phase which is removed by incorporation of spin-orbit coupling in the electronic structure calculations.
The ab initio calculation of spectra of open shell diatomic molecules
Tennyson, Jonathan; Lodi, Lorenzo; McKemmish, Laura K.; Yurchenko, Sergei N.
2016-05-01
The spectra (rotational, rotation-vibrational or electronic) of diatomic molecules due to transitions involving only closed-shell (1Σ ) electronic states follow very regular, simple patterns and their theoretical analysis is usually straightforward. On the other hand, open-shell electronic states lead to more complicated spectral patterns and, moreover, often appear as a manifold of closely lying electronic states, leading to perturbed spectra of even greater complexity. This is especially true when at least one of the atoms is a transition metal. Traditionally these complex cases have been analysed using approaches based on perturbation theory, with semi-empirical parameters determined by fitting to spectral data. Recently the needs of two rather diverse scientific areas have driven the demand for improved theoretical models of open-shell diatomic systems based on an ab initio approach; these areas are ultracold chemistry and the astrophysics of ‘cool’ stars, brown dwarfs and most recently extrasolar planets. However, the complex electronic structure of these molecules combined with the accuracy requirements of high-resolution spectroscopy render such an approach particularly challenging. This review describes recent progress in developing methods for directly solving the effective Schrödinger equation for open-shell diatomic molecules, with a focus on molecules containing a transtion metal. It considers four aspects of the problem: (i) the electronic structure problem; (ii) non-perturbative treatments of the curve couplings; (iii) the solution of the nuclear motion Schrödinger equation; (iv) the generation of accurate electric dipole transition intensities. Examples of applications are used to illustrate these issues.
An ab initio quantum chemical investigation of the structure and stability of ozone-water complexes
Energy Technology Data Exchange (ETDEWEB)
Kumar, Pradeep [Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016 (India); Sathyamurthy, N., E-mail: nsath@iitk.ac.in [Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016 (India); Indian Institute of Science Education and Research Mohali, Sector 81, SAS Nagar, Manauli 140306 (India)
2013-03-29
Highlights: ► Eclipse geometry most stable for the 1:1 ozone-water complex. ► Cyclic structure most stable for the 1:2 complex. ► Shift in the vertical electronic excitation energy of ozone due to hydration. - Abstract: Ab initio quantum chemical calculations have been carried out to investigate the structure and stability of 1:1 and 1:2 ozone-water complexes. All the geometries have been optimized at the CCSD level of theory using aug-cc-pVDZ and aug-cc-pVTZ basis sets. The importance of correlation-consistent basis sets in deciding the nature of critical points on these complexes is emphasized. An analysis based on the dipole moment of the complexes and the charge distribution on atoms follows. The effect of ozone molecule on the structure and properties of water dimer is also investigated. Values of the vertical electronic excitation energy and the corresponding transition dipole moment have been calculated for the ozone-water complexes using the multi-reference-configuration-interaction method and the aug-cc-pVTZ basis set. The calculated shift in vibrational frequencies due to complex formation is compared with the earlier reported experimental and theoretical values.
Laser spectroscopy and ab initio studies of metal-containing free radicals
Greetham, G M
2000-01-01
strontium-containing free radical is reported, that of SrCCH. This new excited electronic state is accessed by the orbitally-forbidden B-tilde' sup 2 DELTA-X-tilde sup 2 SIGMA sup + transition. Spin-orbit and vibrational structure have been seen in spectra of SrCCH and SrCCD and confirmed the assignment. Finally, observation of a new transition in an unidentified gallium-containing molecule is reported. Two progressions corresponding to two different vibrational modes of the molecule are seen in the spectrum. Potential spectral carriers, including Ga sub x clusters and other gallium-containing molecules formed by reaction with impurities, are discussed in an attempt to explain the observed spectrum. This work describes the use of laser spectroscopy and ab initio calculations in the investigation of several new electronic transitions in metal-containing free radicals. These free radicals were prepared in a supersonic jet by laser ablation of solid metal samples in the presence of appropriate precursor molecule...
Directory of Open Access Journals (Sweden)
Lei Li
2015-01-01
Full Text Available The ab initio calculations about the properties of the interstitials doping in the rutile TiO2 and their impact on the transport coefficients are reported. As the doping of the Zr or Ti interstitials in the TiO2, the lattice Ti4+ ions acquire the excess electrons so reduced to the Ti3+ or Ti2+ ions. However, the Cu interstitials could not lose enough electrons to reduce the lattice Ti4+ ions. Furthermore, the Ti or Cu interstitials in the ZrO2 also are unable to promote the lattice Zr4+ ions to form the lattice Zr3+ or Zr2+ ions. The high transport coefficients are observed in the defected TiO2 with the Ti or Zr interstitials as the high concentration of the Ti3+ or Ti2+ ions. So, the Zr interstitials are the favorable choice for the extra-doping to improve the transport properties in the TiO2-based resistive random access memory.
Formation of star nanowires of sulfur-doped zinc oxide: Ab initio calculations
Lin, Qiu-Bao; Wu, Shun-Qing; Zhu, Zi-Zhong
2016-09-01
ZnO nanowires are hexagonally shaped under normal growth conditions, but are transformed from a hexagon to hexagram ones when sulfur dopants are added into the growth solution. The formation mechanism of the hexagram-shaped ZnO nanowires is further studied by the ab initio calculations in this paper. The present calculations support the fact that the hexagonally shaped ZnO nanowires are transformed to hexagram shaped ones when the O atoms on the side surfaces of the nanowires are replaced by S atoms in certain quantities. It indicates that the ratio of sulfur content plays an important role in the hexagram formation. The results of the electronic charge densities indicate that the charge transfer makes the S-Zn bond longer than that of O-Zn. The new charge distribution on the side planes due to the S atoms replacement leads to the formation of the hexagram-shaped nanowires. The calculation on the electronic properties shows that a sulfur-doped hexagram ZnO nanowire is an indirect band gap semiconductor with a narrow gap. When dopant is increased, the gap will decrease.
Silicon and Germanium Nanostructures for Photovoltaic Applications: Ab-Initio Results
Directory of Open Access Journals (Sweden)
Pulci Olivia
2010-01-01
Full Text Available Abstract Actually, most of the electric energy is being produced by fossil fuels and great is the search for viable alternatives. The most appealing and promising technology is photovoltaics. It will become truly mainstream when its cost will be comparable to other energy sources. One way is to significantly enhance device efficiencies, for example by increasing the number of band gaps in multijunction solar cells or by favoring charge separation in the devices. This can be done by using cells based on nanostructured semiconductors. In this paper, we will present ab-initio results of the structural, electronic and optical properties of (1 silicon and germanium nanoparticles embedded in wide band gap materials and (2 mixed silicon-germanium nanowires. We show that theory can help in understanding the microscopic processes important for devices performances. In particular, we calculated for embedded Si and Ge nanoparticles the dependence of the absorption threshold on size and oxidation, the role of crystallinity and, in some cases, the recombination rates, and we demonstrated that in the case of mixed nanowires, those with a clear interface between Si and Ge show not only a reduced quantum confinement effect but display also a natural geometrical separation between electron and hole.
Neukirch, Amanda; Nei, Wanyi; Pedesseau, Laurent; Even, Jacky; Katan, Claudine; Mohite, Aditya; Tretiak, Segrei
2015-03-01
The need for an inexpensive, clean, and plentiful source of energy has generated large amounts of research in an assortment of solution processed organic and hybrid organic-inorganic solar cells. A relative newcomer to the field of solution processed photovoltaics is the lead halide perovskite solar cell. In the past 5 years, the efficiencies of devices made from this material have increased from 3.5% to nearly 20%. Despite the rapid development of organic-inorganic perovskite solar cells, a thorough understanding of the fundamental photophysical processes driving the high performance of these devices is not well understood. I am using state-of-the-art ab initio computational techniques in order to characterize the properties at the interface of perovskite devices in order to aide in materials design and device engineering. I will present an in-depth analysis of the electronic and optical properties of bulk and surface states of pure and mixed halide systems. The high-level static quantum mechanical calculations, including spin-orbit-coupling and the many body GW approach, identify the key electronic states involved in photoinduced dynamics. This knowledge provides important information on how the optical properties change with variations to the system. Supported by the DOE, the LANL LDRD program XW11, and CNLS.
Brandt, Erik G.; Agosta, Lorenzo; Lyubartsev, Alexander P.
2016-07-01
Small-sized wet TiO2 nanoparticles have been investigated by ab initio molecular dynamics simulations. Chemical and physical adsorption of water on the TiO2-water interface was studied as a function of water content, ranging from dry nanoparticles to wet nanoparticles with monolayer coverage of water. The surface reactivity was shown to be a concave function of water content and driven by surface defects. The local coordination number at the defect was identified as the key factor to decide whether water adsorption proceeds through dissociation or physisorption on the surface. A consistent picture of TiO2 nanoparticle wetting at the microscopic level emerges, which corroborates existing experimental data and gives further insight into the molecular mechanisms behind nanoparticle wetting. These calculations will facilitate the engineering of metal oxide nanoparticles with a controlled catalytic water activity.Small-sized wet TiO2 nanoparticles have been investigated by ab initio molecular dynamics simulations. Chemical and physical adsorption of water on the TiO2-water interface was studied as a function of water content, ranging from dry nanoparticles to wet nanoparticles with monolayer coverage of water. The surface reactivity was shown to be a concave function of water content and driven by surface defects. The local coordination number at the defect was identified as the key factor to decide whether water adsorption proceeds through dissociation or physisorption on the surface. A consistent picture of TiO2 nanoparticle wetting at the microscopic level emerges, which corroborates existing experimental data and gives further insight into the molecular mechanisms behind nanoparticle wetting. These calculations will facilitate the engineering of metal oxide nanoparticles with a controlled catalytic water activity. Electronic supplementary information (ESI) available: Simulation data on equilibration of energies and structures (root-mean-square-deviations and
Allen, B. Danette; Alexandrov, Natalia
2016-01-01
Incremental approaches to air transportation system development inherit current architectural constraints, which, in turn, place hard bounds on system capacity, efficiency of performance, and complexity. To enable airspace operations of the future, a clean-slate (ab initio) airspace design(s) must be considered. This ab initio National Airspace System (NAS) must be capable of accommodating increased traffic density, a broader diversity of aircraft, and on-demand mobility. System and subsystem designs should scale to accommodate the inevitable demand for airspace services that include large numbers of autonomous Unmanned Aerial Vehicles and a paradigm shift in general aviation (e.g., personal air vehicles) in addition to more traditional aerial vehicles such as commercial jetliners and weather balloons. The complex and adaptive nature of ab initio designs for the future NAS requires new approaches to validation, adding a significant physical experimentation component to analytical and simulation tools. In addition to software modeling and simulation, the ability to exercise system solutions in a flight environment will be an essential aspect of validation. The NASA Langley Research Center (LaRC) Autonomy Incubator seeks to develop a flight simulation infrastructure for ab initio modeling and simulation that assumes no specific NAS architecture and models vehicle-to-vehicle behavior to examine interactions and emergent behaviors among hundreds of intelligent aerial agents exhibiting collaborative, cooperative, coordinative, selfish, and malicious behaviors. The air transportation system of the future will be a complex adaptive system (CAS) characterized by complex and sometimes unpredictable (or unpredicted) behaviors that result from temporal and spatial interactions among large numbers of participants. A CAS not only evolves with a changing environment and adapts to it, it is closely coupled to all systems that constitute the environment. Thus, the ecosystem that
Ab initio STM and STS simulations on magnetic and nonmagnetic metallic surfaces
Energy Technology Data Exchange (ETDEWEB)
Dick, Alexey
2008-04-14
The aim of this work was to provide an in-depth understanding of a new generation of scan- ning tunneling microscopy experiments, performed employing different regimes of the STM: the spectroscopy-mode (the so-called Fourier Transformed STM, FT-STM), and the spin-sensitive mode (the so-called spin-polarized STM, SP-STM). In the present thesis ab initio tools are proposed that are based on DFT calculations to theoretically predict and analyze such types of the STM. The first part of this thesis focusses on the simulation of FT-STM, the mode that allows to probe local dispersion properties of the electrons at the surface. In order to provide the theoretical counterpart of the experimental FT-STM spectra we have introduced a new implicit approach that is derived from Tersoff-Hamann theory of the STM. The importance of an accurate description of surface wavefunctions at 5-15 A above the surface as well as the spurious quantum- size effects have been discussed in detail together with approaches to obtain converged FT-STM images. We applied our method to FT-STM experiments performed on Ag(110) surfaces. In the second part of the thesis we discuss the modeling of the spin-resolved STM, the mode that allows to characterize the magnetic structure of a surface. As a case system we studied here the magnetically-ordered transition-metal nitride surface Mn{sub 3}N{sub 2}(010). Because SP-STM experiments did not allow a conclusive understanding of the surface structure, we have first employed ab initio thermodynamics to figure out the most stable magnetic and atomic configuration of the surface that are consistent with experiments. To simulate SP-STM images on the most stable Mn{sub 3}N{sub 2}(010) surface we have employed the spin-generalized transfer-Hamiltonian formalism, assuming that the tip wavefunctions have dominant radial symmetry (s-like tip). (orig.)
Study of atomic structure of liquid Hg-In alloys using ab-initio molecular dynamics
Energy Technology Data Exchange (ETDEWEB)
Sharma, Nalini; Ahluwalia, P. K. [Department of Physics, Himachal Pradesh University, Shimla(HP)-171005 (India); Thakur, Anil [Department of Physics, Govt. P. G. College Solan (HP)-173212 (India)
2015-05-15
Ab-initio molecular dynamics simulations are performed to study the structural properties of liquid Hg-In alloys. The interatomic interactions are described by ab-initio pseudopotentials given by Troullier and Martins. Five liquid Hg-In mixtures (Hg{sub 10}In{sub 90}, Hg{sub 30}In{sub 70}, Hg{sub 50}In{sub 50}, Hg{sub 70}In{sub 30} and Hg{sub 90}In{sub 10}) at 299K are considered. The radial distribution function g(r) and structure factor S(q) of considered alloys are compared with respective experimental results for liquid Hg (l-Hg) and (l-In). The radial distribution function g(r) shows the presence of short range order in the systems considered. Smooth curves of Bhatia-Thornton partial structure factors factor shows the presence of liquid state in the considered alloys.
Conformational space of clindamycin studied by ab initio and full-atom molecular dynamics.
Kulczycka-Mierzejewska, Katarzyna; Trylska, Joanna; Sadlej, Joanna
2016-01-01
Molecular dynamics (MD) simulations allow determining internal flexibility of molecules at atomic level. Using ab initio Born-Oppenheimer molecular dynamics (BOMD), one can simulate in a reasonable time frame small systems with hundreds of atoms, usually in vacuum. With quantum mechanics/molecular mechanics (QM/MM) or full-atom molecular dynamics (FAMD), the influence of the environment can also be simulated. Here, we compare three types of MD calculations: ab initio BOMD, hybrid QM/MM, and classical FAMD. As a model system, we use a small antibiotic molecule, clindamycin, which is one of the lincosamide antibiotics. Clindamycin acquires two energetically stable forms and we investigated the transition between these two experimentally known conformers. We performed 60-ps BOMD simulations in vacuum, 50-ps QM/MM, and 100-ns FAMD in explicit water. The transition between two antibiotic conformers was observed using both BOMD and FAMD methods but was not noted in the QM/MM simulations.
Raman spectroscopy, ab-initio model calculations, and conformational, equilibria in ionic liquids
DEFF Research Database (Denmark)
Berg, Rolf W.
2009-01-01
spectroscopy and ab-initio molecular orbital calculations. A discussion is given, based mainly on some recent FT- Raman spectroscopic results on the model ionic liquid system of 1-butyl-3-methyl-imidazolium ([C4C1Im]+X-) salts. The rotational isomerism of the [C4C1Im]+ cation is described: the presence of anti......A review of the recent developments in the study and understanding of room temperature ionic liquids are given. An intimate picture of how and why these liquids are not crystals at ambient conditions is attempted, based on evidence from crystallographical results combined with vibrational.......3 Brief introduction to ab-initio model calculations .... 312 12.4 Case study on Raman spectroscopy and structure of imidazolium-based ionic liquids ..... 312 12.5 Raman spectra and structure of [C4C1Im]+ liquids ..... 315 12.6 Normal mode analysis and rotational isomerism of the [C4C1Im]+ cation...
Ab Initio No-Core Shell Model Calculations Using Realistic Two- and Three-Body Interactions
Energy Technology Data Exchange (ETDEWEB)
Navratil, P; Ormand, W E; Forssen, C; Caurier, E
2004-11-30
There has been significant progress in the ab initio approaches to the structure of light nuclei. One such method is the ab initio no-core shell model (NCSM). Starting from realistic two- and three-nucleon interactions this method can predict low-lying levels in p-shell nuclei. In this contribution, we present a brief overview of the NCSM with examples of recent applications. We highlight our study of the parity inversion in {sup 11}Be, for which calculations were performed in basis spaces up to 9{Dirac_h}{Omega} (dimensions reaching 7 x 10{sup 8}). We also present our latest results for the p-shell nuclei using the Tucson-Melbourne TM three-nucleon interaction with several proposed parameter sets.
Emergent properties of nuclei from ab initio coupled-cluster calculations
Hagen, G; Hjorth-Jensen, M; Papenbrock, T
2016-01-01
Emergent properties such as nuclear saturation and deformation, and the effects on shell structure due to the proximity of the scattering continuum and particle decay channels are fascinating phenomena in atomic nuclei. In recent years, ab initio approaches to nuclei have taken the first steps towards tackling the computational challenge of describing these phenomena from Hamiltonians with microscopic degrees of freedom. This endeavor is now possible due to ideas from effective field theories, novel optimization strategies for nuclear interactions, ab initio methods exhibiting a soft scaling with mass number, and ever-increasing computational power. This paper reviews some of the recent accomplishments. We also present new results. The recently optimized chiral interaction NNLO$_{\\rm sat}$ is shown to provide an accurate description of both charge radii and binding energies in selected light- and medium-mass nuclei up to $^{56}$Ni. We derive an efficient scheme for including continuum effects in coupled-clust...
Interatomic potentials for Al and Ni from experimental data and ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Mishin, Y.; Farkas, D.; Miehl, M.J.; Papaconstantopoulos, D.A.
1999-07-01
New embedded-atom potentials for Al and Ni have been developed by fitting to both experimental data and the results of ab initio calculations. The ab initio data were obtained in the form of energies of different alternative computer-generated crystalline structures of these metals. The potentials accurately reproduce basic equilibrium properties of Al and Ni such as the elastic constants, phonon dispersion curves, vacancy formation and migration energies, stacking fault energies, and surface energies. The equilibrium energies of various alternative structures not included in the fitting database are calculated with these potentials. The results are compared with predictions of total-energy tight-binding calculations for the same structures. The embedded-atom potentials correctly reproduce the structural stability trends, which suggests that they are transferable to different local environments encountered in atomistic simulations of lattice defects.
Low-temperature metallic liquid hydrogen: an ab-initio path-integral molecular dynamics perspective
Chen, Ji; Li, Xin-Zheng; Zhang, Qianfan; Probert, Matthew; Pickard, Chris; Needs, Richard; Michaelides, Angelos; Wang, Enge
2013-03-01
Experiments and computer simulations have shown that the melting temperature of solid hydrogen drops with pressure above about 65 GPa, suggesting that a low temperature liquid state might exist. It has also been suggested that this liquid state might be non-molecular and metallic, although evidence for such behaviour is lacking. Using a combination of ab initio path-integral molecular dynamics and the two-phase methods, we have simulated the melting of solid hydrogen under finite temperatures. We found an atomic solid phase from 500 to 800 GPa which melts at < 200 K. Beyond this and up to pressures of 1,200 GPa a metallic atomic liquid is stable at temperatures as low as 50 K. The quantum motion of the protons is critical to the low melting temperature in this system as ab initio simulations with classical nuclei lead to a considerably higher melting temperature of ~300 K across the entire pressure range considered.
Electrical Resistivity of Na-K Binary Liquid Alloy Using Ab-Initio Pseudopotentials
Institute of Scientific and Technical Information of China (English)
Anil Thakur; P. K. Ahluwalia
2005-01-01
@@ The study of electrical resistivity of simple binary liquid alloy Na-K is presented as a function of concentration.Hard sphere diameters of sodium (Na) and potassium (K) are obtained through the inter ionic pair potentials evaluated using Troullier and Martins ab-initio pseudopotentials, which have been used to calculate partial structure factors S(q). The Ziman formula for calculating resistivity of binary liquid alloys has been used. Form factors are calculated using ab-initio pseudopotentials. The results suggest that the first principle approach for calculating pseudopotentials with in the frame work of Ziman formalism is quite successful in explaining the electrical resistivity data of compound forming binary liquid alloys.
Bridging a gap between continuum-QCD and ab initio predictions of hadron observables
Directory of Open Access Journals (Sweden)
Daniele Binosi
2015-03-01
Full Text Available Within contemporary hadron physics there are two common methods for determining the momentum-dependence of the interaction between quarks: the top-down approach, which works toward an ab initio computation of the interaction via direct analysis of the gauge-sector gap equations; and the bottom-up scheme, which aims to infer the interaction by fitting data within a well-defined truncation of those equations in the matter sector that are relevant to bound-state properties. We unite these two approaches by demonstrating that the renormalisation-group-invariant running-interaction predicted by contemporary analyses of QCD's gauge sector coincides with that required in order to describe ground-state hadron observables using a nonperturbative truncation of QCD's Dyson–Schwinger equations in the matter sector. This bridges a gap that had lain between nonperturbative continuum-QCD and the ab initio prediction of bound-state properties.
{\\it Ab initio} nuclear structure - the large sparse matrix eigenvalue problem
Vary, James P; Ng, Esmond; Yang, Chao; Sosonkina, Masha
2009-01-01
The structure and reactions of light nuclei represent fundamental and formidable challenges for microscopic theory based on realistic strong interaction potentials. Several {\\it ab initio} methods have now emerged that provide nearly exact solutions for some nuclear properties. The {\\it ab initio} no core shell model (NCSM) and the no core full configuration (NCFC) method, frame this quantum many-particle problem as a large sparse matrix eigenvalue problem where one evaluates the Hamiltonian matrix in a basis space consisting of many-fermion Slater determinants and then solves for a set of the lowest eigenvalues and their associated eigenvectors. The resulting eigenvectors are employed to evaluate a set of experimental quantities to test the underlying potential. For fundamental problems of interest, the matrix dimension often exceeds $10^{10}$ and the number of nonzero matrix elements may saturate available storage on present-day leadership class facilities. We survey recent results and advances in solving t...
[Photoelectron Spectra of CCl2-: Ab Initio Calculation and Franck-Condon Analysis].
Wu, Jun
2015-12-01
Geometry optimization and harmonic vibrational frequency calculations were performed on the X¹A₁ state of CCl₂ and X²B₁ state of CCl₂⁻ at the B3LYP, MP2, CCSD levels. Franck-Condon analysis and spectral simulations were carried out on the photoelectron band of CCl₂⁻ including Duschinsky effects. The simulated spectra obtained are in excellent agreement with the experiment. Note that Duschinsky effect between bending vibration and the symmetric stretch modes should be considered in the CCl₂ (X¹A₁)-CCl₂⁻ (X²B₁) photodetachment process. By combining ab initio calculations with Franck-Condon analyses, the assignment of spectrum observed is firmly established to the X¹A₁-X²B₁ photodetachment process of the CCl₂⁻ radical, and the recommended geometric parameters of which in the literature are confirmed again base on ab initio theory and IFCA process.
Ab initio molecular dynamics simulation of liquid water by quantum Monte Carlo
Energy Technology Data Exchange (ETDEWEB)
Zen, Andrea, E-mail: a.zen@ucl.ac.uk [Dipartimento di Fisica, “La Sapienza” - Università di Roma, piazzale Aldo Moro 5, 00185 Rome (Italy); London Centre for Nanotechnology, University College London, London WC1E 6BT (United Kingdom); Luo, Ye, E-mail: xw111luoye@gmail.com; Mazzola, Guglielmo, E-mail: gmazzola@phys.ethz.ch; Sorella, Sandro, E-mail: sorella@sissa.it [SISSA–International School for Advanced Studies, Via Bonomea 26, 34136 Trieste (Italy); Democritos Simulation Center CNR–IOM Istituto Officina dei Materiali, 34151 Trieste (Italy); Guidoni, Leonardo, E-mail: leonardo.guidoni@univaq.it [Dipartimento di Fisica, “La Sapienza” - Università di Roma, piazzale Aldo Moro 5, 00185 Rome (Italy); Dipartimento di Scienze Fisiche e Chimiche, Università degli Studi dell’ Aquila, via Vetoio, 67100 L’ Aquila (Italy)
2015-04-14
Although liquid water is ubiquitous in chemical reactions at roots of life and climate on the earth, the prediction of its properties by high-level ab initio molecular dynamics simulations still represents a formidable task for quantum chemistry. In this article, we present a room temperature simulation of liquid water based on the potential energy surface obtained by a many-body wave function through quantum Monte Carlo (QMC) methods. The simulated properties are in good agreement with recent neutron scattering and X-ray experiments, particularly concerning the position of the oxygen-oxygen peak in the radial distribution function, at variance of previous density functional theory attempts. Given the excellent performances of QMC on large scale supercomputers, this work opens new perspectives for predictive and reliable ab initio simulations of complex chemical systems.
Ab-initio molecular modeling of interfaces in tantalum-carbon system
Energy Technology Data Exchange (ETDEWEB)
Balani, Kantesh; Mungole, Tarang [Materials Science and Engineering, Indian Institute of Technology, Kanpur-208016 (India); Bakshi, Srinivasa Rao [Mechanical and Materials Engineering, Florida International University, Miami, Florida 33174 (United States); Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Agarwal, Arvind [Mechanical and Materials Engineering, Florida International University, Miami, Florida 33174 (United States)
2012-03-15
Processing of ultrahigh temperature TaC ceramic material with sintering additives of B{sub 4}C and reinforcement of carbon nanotubes (CNTs) gives rise to possible formation of several interfaces (Ta{sub 2}C-TaC, TaC-CNT, Ta{sub 2}C-CNT, TaB{sub 2}-TaC, and TaB{sub 2}-CNT) that could influence the resultant properties. Current work focuses on interfaces developed during spark plasma sintering of TaC-system and performing ab initio molecular modeling of the interfaces generated during processing of TaC-B{sub 4}C and TaC-CNT composites. The energy of the various interfaces has been evaluated and compared with TaC-Ta{sub 2}C interface. The iso-surface electronic contours are extracted from the calculations eliciting the enhanced stability of TaC-CNT interface by 72.2%. CNTs form stable interfaces with Ta{sub 2}C and TaB{sub 2} phases with a reduction in the energy by 35.8% and 40.4%, respectively. The computed Ta-C-B interfaces are also compared with experimentally observed interfaces in high resolution TEM images.
Optimized energy landscape exploration using the ab initio based activation-relaxation technique
Machado-Charry, Eduardo; Béland, Laurent Karim; Caliste, Damien; Genovese, Luigi; Deutsch, Thierry; Mousseau, Normand; Pochet, Pascal
2011-07-01
Unbiased open-ended methods for finding transition states are powerful tools to understand diffusion and relaxation mechanisms associated with defect diffusion, growth processes, and catalysis. They have been little used, however, in conjunction with ab initio packages as these algorithms demanded large computational effort to generate even a single event. Here, we revisit the activation-relaxation technique (ART nouveau) and introduce a two-step convergence to the saddle point, combining the previously used Lanczós algorithm with the direct inversion in interactive subspace scheme. This combination makes it possible to generate events (from an initial minimum through a saddle point up to a final minimum) in a systematic fashion with a net 300-700 force evaluations per successful event. ART nouveau is coupled with BigDFT, a Kohn-Sham density functional theory (DFT) electronic structure code using a wavelet basis set with excellent efficiency on parallel computation, and applied to study the potential energy surface of C20 clusters, vacancy diffusion in bulk silicon, and reconstruction of the 4H-SiC surface.
Patil, Amol Baliram; Bhanage, Bhalchandra Mahadeo
2016-06-21
The nature of bonding interactions between the cation and the anion of an ionic liquid is at the heart of understanding ionic liquid properties. A particularly interesting case is a special class of ionic liquids known as protic ionic liquids. The extent of proton transfer in protic ionic liquids has been observed to vary according to the interacting species. Back proton transfer renders protic ionic liquids volatile and to be considered as inferior ionic liquids. We try to address this issue by employing modern ab initio valence bond theory calculations. The results indicate that the bonding in the cation and the anion of a prototypical ionic liquid, ethylammonium nitrate, is fundamentally different. It is neither characteristic of covalent/polar covalent bonding nor ionic bonding but rather charge shift bonding as a resonance hybrid of two competing ionic molecular electronic structure configurations. An investigation of other analogous protic ionic liquids reveals that this charge shift bonding seems to be a typical characteristic of protic ionic liquids while the ionic solid analogue compound ammonium nitrate has less charge shift bonding character as compared to protic ionic liquids. Further the extent of charge shift bonding character has been found to be congruent with the trends in many physicochemical properties such as melting point, conductivity, viscosity, and ionicity of the studied ionic liquids indicating that percentage charge shift character may serve as a key descriptor for large scale computational screening of ionic liquids with desired properties.
Rafiee, Marjan; Javaheri, Masoumeh
2015-01-01
Tyrosinase is a multifunctional copper-containing enzyme. It can catalyze two distinct reactions of melanin synthesis and benzaldehyde derivatives, which are potential tyrosinase inhibitors. To find the relationships between charge distributions of benzaldehyde and their pharmaceutical behavior, the present study aimed at investigating nuclear quadrupole coupling constants of quadrupolare nuclei in the functional benzaldehyde group and calculating some its derivatives. In addition, the differences between the electronic structures of various derivatives of this depigmenting drug were examined. All ab initio calculations were carried out using Gaussian 03. The results predicted benzaldehyde derivatives to be bicentral inhibitors; nevertheless, the oxygen or hydrogen contents of the aldehyde group were not found to be the only active sites. Furthermore with the presence of the aldehyde group, the terminal methoxy group in C4 was found to contribute to tyrosinase inhibitory activities. In addition, an oxygen atom with high charge density in the side chain was found to play an important role in its inhibitory effect. PMID:27844007
Directory of Open Access Journals (Sweden)
Marjan Rafiee
2015-09-01
Full Text Available Tyrosinase is a multifunctional copper-containing enzyme. It can catalyze two distinct reactions of melanin synthesis and benzaldehyde derivatives, which are potential tyrosinase inhibitors. To find the relationships between charge distributions of benzaldehyde and their pharmaceutical behavior, the present study aimed at investigating nuclear quadrupole coupling constants of quadrupolare nuclei in the functional benzaldehyde group and calculating some its derivatives. In addition, the differences between the electronic structures of various derivatives of this depigmenting drug were examined. All ab initio calculations were carried out using Gaussian 03. The results predicted benzaldehyde derivatives to be bicentral inhibitors; nevertheless, the oxygen or hydrogen contents of the aldehyde group were not found to be the only active sites. Furthermore with the presence of the aldehyde group, the terminal methoxy group in C4 was found to contribute to tyrosinase inhibitory activities. In addition, an oxygen atom with high charge density in the side chain was found to play an important role in its inhibitory effect.
Communication: Towards ab initio self-energy embedding theory in quantum chemistry
Energy Technology Data Exchange (ETDEWEB)
Lan, Tran Nguyen, E-mail: latran@umich.edu [Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109 (United States); Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States); Kananenka, Alexei A.; Zgid, Dominika [Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109 (United States)
2015-12-28
The self-energy embedding theory (SEET), in which the active space self-energy is embedded in the self-energy obtained from a perturbative method treating the non-local correlation effects, was recently developed in our group. In SEET, the double counting problem does not appear and the accuracy can be improved either by increasing the perturbation order or by enlarging the active space. This method was first calibrated for the 2D Hubbard lattice showing promising results. In this paper, we report an extension of SEET to quantum chemical ab initio Hamiltonians for applications to molecular systems. The self-consistent second-order Green’s function method is used to describe the non-local correlations, while the full configuration interaction method is carried out to capture strong correlation within the active space. Using few proof-of-concept examples, we show that SEET yields results of comparable quality to n-electron valence state second-order perturbation theory with the same active space, and furthermore, the full active space can be split into smaller active spaces without further implementation. Moreover, SEET avoids intruder states and does not require any high-order reduced density matrices. These advantages show that SEET is a promising method to describe physical and chemical properties of challenging molecules requiring large active spaces.
Slavíček, Petr; Fárník, Michal
2011-07-14
In this perspective article, we focus on the photochemistry of five-membered nitrogen containing heterocycles (pyrrole, imidazole and pyrazole) in clusters. These heterocycles represent paradigmatic structures for larger biologically active heterocyclic molecules and complexes. The dimers of the three molecules are also archetypes of different bonding patterns: N-H···π interaction, N-H···N hydrogen bond and double hydrogen bond. We briefly review available data on photochemistry of the title molecules in the gas phase, but primarily we focus on the new reaction channels opened upon the complexation with other heterocycles or solvent molecules. Based on ab initio calculations we discuss various possible reactions in the excited states of the clusters: (1) hydrogen dissociation, (2) hydrogen transfer between the heterocyclic units, (3) molecular ring distortion, and (4) coupled electron-proton transfer. The increasing photostability with complexity of the system can be inferred from experiments with photodissociation in these clusters. A unified view on photoinduced processes in five-membered N-heterocycles is provided. We show that even though different deactivation channels are energetically possible for the complexed heterocycles, in most cases the major result is a fast reconstruction of the ground state. The complexed or solvated heterocycles are thus inherently photostable although the stability can in principle be achieved via different reaction routes.
Beyond Born-Mayer: Improved models for short-range repulsion in ab initio force fields
Van Vleet, Mary J; Stone, Anthony J; Schmidt, J R
2016-01-01
Short-range repulsion within inter-molecular force fields is conventionally described by either Lennard-Jones (${A}/{r^{12}}$) or Born-Mayer ($A\\exp(-Br)$) forms. Despite their widespread use, these simple functional forms are often unable to describe the interaction energy accurately over a broad range of inter-molecular distances, thus creating challenges in the development of ab initio force fields and potentially leading to decreased accuracy and transferability. Herein, we derive a novel short-range functional form based on a simple Slater-like model of overlapping atomic densities and an iterated stockholder atom (ISA) partitioning of the molecular electron density. We demonstrate that this Slater-ISA methodology yields a more accurate, transferable, and robust description of the short-range interactions at minimal additional computational cost compared to standard Lennard-Jones or Born-Mayer approaches. Finally, we show how this methodology can be adapted to yield the standard Born-Mayer functional for...
Optimized energy landscape exploration using the ab initio based activation-relaxation technique.
Machado-Charry, Eduardo; Béland, Laurent Karim; Caliste, Damien; Genovese, Luigi; Deutsch, Thierry; Mousseau, Normand; Pochet, Pascal
2011-07-21
Unbiased open-ended methods for finding transition states are powerful tools to understand diffusion and relaxation mechanisms associated with defect diffusion, growth processes, and catalysis. They have been little used, however, in conjunction with ab initio packages as these algorithms demanded large computational effort to generate even a single event. Here, we revisit the activation-relaxation technique (ART nouveau) and introduce a two-step convergence to the saddle point, combining the previously used Lanczós algorithm with the direct inversion in interactive subspace scheme. This combination makes it possible to generate events (from an initial minimum through a saddle point up to a final minimum) in a systematic fashion with a net 300-700 force evaluations per successful event. ART nouveau is coupled with BigDFT, a Kohn-Sham density functional theory (DFT) electronic structure code using a wavelet basis set with excellent efficiency on parallel computation, and applied to study the potential energy surface of C(20) clusters, vacancy diffusion in bulk silicon, and reconstruction of the 4H-SiC surface.
Towards ab initio self-energy embedding theory in quantum chemistry
Lan, Tran Nguyen; Zgid, Dominika
2015-01-01
The self-energy embedding theory (SEET), in which the active space self-energy is embedded in the self-energy obtained from a perturbative method treating the non-local correlation effects, was recently developed in our group. In SEET the double counting problem does not appear and the accuracy can be improved either by increasing the perturbation order or by enlarging the active space. This method was first calibrated for the 2D Hubbard lattice showing promising results. In this paper, we report an extension of SEET to quantum chemical ab initio Hamiltonians for applications to molecular systems. The self-consistent second-order Green's function (GF2) method is used to describe the non-local correlations, while the full configuration interaction (FCI) method is carried out to capture strong correlation within the active space. Using few proof-of-concept examples, we show that SEET yields results of comparable quality to $n-$electron valence state second-order perturbation theory (NEVPT2) with the same active...
Can DNA-binding proteins of replisome tautomerize nucleotide bases? Ab initio model study.
Brovarets', Ol'ha O; Yurenko, Yevgen P; Dubey, Igor Ya; Hovorun, Dmytro M
2012-01-01
Ab initio quantum-chemical study of specific point contacts of replisome proteins with DNA modeled by acetic acid with canonical and mutagenic tautomers of DNA bases methylated at the glycosidic nitrogen atoms was performed in vacuo and continuum with a low dielectric constant (ϵ ∼ 4) corresponding to a hydrophobic interface of protein-nucleic acid interaction. All tautomerized complexes were found to be dynamically unstable, because the electronic energies of their back-reaction barriers do not exceed zero-point vibrational energies associated with the vibrational modes whose harmonic vibrational frequencies become imaginary in the transition states of the tautomerization reaction. Additionally, based on the physicochemical arguments, it was demonstrated that the effects of biomolecular environment cannot ensure dynamic stabilization. This result allows suggesting that hypothetically generated by DNA-binding proteins of replisome rare tautomers will have no impact on the total spontaneous mutation due to the low reverse barrier allowing a quick return to the canonical form.
Communication: Towards ab initio self-energy embedding theory in quantum chemistry.
Lan, Tran Nguyen; Kananenka, Alexei A; Zgid, Dominika
2015-12-28
The self-energy embedding theory (SEET), in which the active space self-energy is embedded in the self-energy obtained from a perturbative method treating the non-local correlation effects, was recently developed in our group. In SEET, the double counting problem does not appear and the accuracy can be improved either by increasing the perturbation order or by enlarging the active space. This method was first calibrated for the 2D Hubbard lattice showing promising results. In this paper, we report an extension of SEET to quantum chemical ab initio Hamiltonians for applications to molecular systems. The self-consistent second-order Green's function method is used to describe the non-local correlations, while the full configuration interaction method is carried out to capture strong correlation within the active space. Using few proof-of-concept examples, we show that SEET yields results of comparable quality to n-electron valence state second-order perturbation theory with the same active space, and furthermore, the full active space can be split into smaller active spaces without further implementation. Moreover, SEET avoids intruder states and does not require any high-order reduced density matrices. These advantages show that SEET is a promising method to describe physical and chemical properties of challenging molecules requiring large active spaces.
Energy Technology Data Exchange (ETDEWEB)
Fischer, Sean A.; Aprà, Edoardo; Govind, Niranjan; Hess, Wayne P.; El-Khoury, Patrick Z.
2017-02-03
Recent developments in nanophotonics have paved the way for achieving significant advances in the realm of single molecule chemical detection, imaging, and dynamics. In particular, surface-enhanced Raman scattering (SERS) is a powerful analytical technique that is now routinely used to identify the chemical identity of single molecules. Understanding how nanoscale physical and chemical processes affect single molecule SERS spectra and selection rules is a challenging task, and is still actively debated. Herein, we explore underappreciated chemical phenomena in ultrasensitive SERS. We observe a fluctuating excited electronic state manifold, governed by the conformational dynamics of a molecule (4,4’-dimercaptostilbene, DMS) interacting with a metallic cluster (Ag20). This affects our simulated single molecule SERS spectra; the time trajectories of a molecule interacting with its unique local environment dictates the relative intensities of the observable Raman-active vibrational states. Ab initio molecular dynamics of a model Ag20-DMS system are used to illustrate both concepts in light of recent experimental results.
Ab initio study of He trapping, diffusion and clustering in Y2O3
Lai, Wensheng; Ou, Yidian; Lou, Xiaofeng; Wang, Fei
2017-02-01
Ab initio calculations have been performed to study the formation and migration energies of helium atoms and the stability of helium-vacancy clusters in a Y2O3 crystal. The calculated formation energies show that a helium atom is preferred to occupy an yttrium vacancy site with a large volume and low electron density. The migration energy of the helium atom by an interstitial mechanism is 0.31 eV. Calculations of the binding energies of an extra helium atom to the helium-vacancy clusters vary with the number of helium atoms in the clusters with a typical value of 0.4-0.7 eV. This turns negative when the He atoms reach saturation; that indicates that vacancy clusters can attract a limited number of helium atoms to form small stable helium-vacancy clusters. Our calculations suggest that the use of Y2O3 in oxide dispersion strengthened ferritic steels may reduce He gas bubble formation as it may act as sink for trapping helium atoms.
Ab initio ro-vibronic spectroscopy of SiCCl (X{sup ~2}Π)
Energy Technology Data Exchange (ETDEWEB)
Brites, Vincent [Université d’Evry Val d’Essonne, Laboratoire Analyse et Modélisation pour la Biologie et l’Environnement, LAMBE CNRS UMR 8587, Boulevard F. Mitterrand, 91025 Evry Cedex (France); Mitrushchenkov, Alexander O.; Léonard, Céline, E-mail: celine.leonard@u-pem.fr [Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 bd Descartes, 77454 Marne-la-Vallée (France); Peterson, Kirk A. [Department of Chemistry, Washington State University, Pullman, Washington 99164 (United States)
2014-07-21
The full dimensional potential energy surfaces of the {sup 2}A{sup ′} and {sup 2}A{sup ′′} electronic components of X{sup ~2}Π SiCCl have been computed using the explicitly correlated coupled cluster method, UCCSD(T)-F12b, combined with a composite approach taking into account basis set incompleteness, core-valence correlation, scalar relativity, and higher order excitations. The spin-orbit and dipole moment surfaces have also been computed ab initio. The ro-vibronic energy levels and absorption spectrum at 5 K have been determined from variational calculations. The influence of each correction on the fundamental frequencies is discussed. An assignment is proposed for bands observed in the LIF experiment of Smith et al. [J. Chem. Phys. 117, 6446 (2002)]. The overall agreement between the experimental and calculated ro-vibronic levels is better than 7 cm{sup −1} which is comparable with the 10–20 cm{sup −1} resolution of the emission spectrum.
Rosenow, Phil; Tonner, Ralf
2016-05-01
The extent of hydrogen coverage of the Si(001) c(4 × 2) surface in the presence of hydrogen gas has been studied with dispersion corrected density functional theory. Electronic energy contributions are well described using a hybrid functional. The temperature dependence of the coverage in thermodynamic equilibrium was studied computing the phonon spectrum in a supercell approach. As an approximation to these demanding computations, an interpolated phonon approach was found to give comparable accuracy. The simpler ab initio thermodynamic approach is not accurate enough for the system studied, even if corrections by the Einstein model for surface vibrations are considered. The on-set of H2 desorption from the fully hydrogenated surface is predicted to occur at temperatures around 750 K. Strong changes in hydrogen coverage are found between 1000 and 1200 K in good agreement with previous reflectance anisotropy spectroscopy experiments. These findings allow a rational choice for the surface state in the computational treatment of chemical reactions under typical metal organic vapor phase epitaxy conditions on Si(001).