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  • 1
    Electronic Resource
    Electronic Resource
    A correlation potential for molecular systems from the single particle Green's function (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3638-3653 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is well known that the correlated ground state energy can be derived from a knowledge of the single particle Green's function of a system, even though the two density cannot be obtained from it. In this paper it is shown that the single particle Green's function in fact contains more detailed information than the total energy alone, to the extent that the local Slater‘xnLöwdin correlation potential can be obtained from it. This potential can be used as a more detailed criterion to judge the quality of approximate Green's functions than the total energy by itself. The formalism leads moreover to a natural partitioning of the correlation energy into terms depending on the correlation correction to the one density alone and a remaining "true'' correlation contribution. In this paper we calculate the single particle Green's function using the second order approximation to the self-energy for a series of small model systems (He, Be, H2, LiH, and H2O). The correlation potential and the partitioning of the correlation energy are used to analyze this approximation and to assess its accuracy in these systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454884
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  • 2
    Electronic Resource
    Electronic Resource
    Acetylene in nematic liquid crystals: A vibrational analysis of the observed dipolar couplings (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4657-4665 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Experimental dipole couplings for several isotopically substituted modifications of acetylene dissolved in the nematic liquid crystals 1132 (Merck ZLI 1132), EBBA [N-(4-ethoxybenzylidene)-2, 6-dideutero-4-n-butylaniline] and a 55 wt. % 1132/EBBA mixture are obtained from NMR measurements. The dipolar couplings are calculated using a model for the solvent–solute interaction. The interaction is taken to be of second rank tensorial form and the effects of the coupling between the vibrations and rotations are taken into account. The calculated values are in good agreement with the experimental results although some discrepancies exist. These discrepancies are discussed in terms of a possible contribution to the observed carbon–carbon coupling from the anisotropy in the indirect coupling. The results show that the interaction between the vibrations and rotations of the solute plays an important role in determining the observed couplings and that specific interactions with the liquid crystal need not be invoked to explain the results. Previous studies have shown that molecular hydrogen experiences an external electric field gradient due to its liquid crystal environment and that in 55 wt. % 1132/EBBA the value of this field gradient is zero at 301.4 K. It has also been shown that the interaction between this field gradient and the solute molecular quadrupole moment dominates the ordering of molecular hydrogen in liquid crystals, such as 1132 and EBBA, where the field gradient is large. A qualitative analysis indicates that this interaction is important for the ordering of acetylene and that other mechanisms also play a role.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455700
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  • 3
    Electronic Resource
    Electronic Resource
    A comparison between the Møller–Plesset and Green's function perturbative approaches to the calculation of the correlation energy in the many-electron problem (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5826-5837 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The well-known expression for the total energy in terms of the single-particle many-body Green's function is analyzed in detail. In particular the relation between the nth order Møller–Plesset energy and the energy calculated from a Green's function generated by the nth order self-energy is investigated. It is shown how the nth order Møller–Plesset energy can be expressed in terms of the Green's function. The H2 molecule is studied in a minimal basis to serve as a model in which exact results can be easily obtained. Numerical calculations are performed for H2, He, Be, LiH, Ne, HF, H2O, NH3, and CH4 and the results are analyzed in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459578
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  • 4
    Electronic Resource
    Electronic Resource
    Relativistic effects on the optical response of InSb by time-dependent density-functional theory (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 1860-1865 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we show how relativistic effects can be included in the time-dependent density-functional theory (DFT) for the optical response properties of nonmetallic crystals. The dominant scalar relativistic effects have been included using the zeroth-order regular approximation (ZORA) in the ground-state DFT calculations, as well as in the time-dependent response calculations. We show that this theory can also be applied to indium antimonide in the zinc-blende structure, notwithstanding the fact that it turns into a semimetal when scalar relativistic effects are included. Results are given for the band structure, the static dielectric constant ε∞ and the dielectric function ε(ω), for the various levels on which relativity can be included, i.e., nonrelativistic, only in the ground-state, or also in the response calculation. Comparisons of our calculated results are made with experiment and other theoretical investigations. With the inclusion of scalar relativistic effects, the band structure of InSb becomes semimetallic within the local density approximation and we find a deviation of 5% from experiment for the static dielectric constant. Also the dielectric function is improved and the spectra are in good agreement with experiment, although the spectral features are shifted to somewhat lower energies compared to experiment. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1334615
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  • 5
    Electronic Resource
    Electronic Resource
    Current density functional theory for optical spectra: A polarization functional (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 1995-1999 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present a new approach to calculate optical spectra, which for the first time uses a polarization dependent functional within current density functional theory (CDFT), which was proposed by Vignale and Kohn [Phys. Rev. Lett. 77, 2037 (1996)]. This polarization dependent functional includes exchange-correlation (xc) contributions in the effective macroscopic electric field. This functional is used to calculate the optical absorption spectrum of several common semiconductors. We achieved in all cases good agreement with experiment. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1385370
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  • 6
    Electronic Resource
    Electronic Resource
    Efficient real-space approach to time-dependent density functional theory for the dielectric response of nonmetallic crystals (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6517-6531 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-dependent density functional theory has been used to calculate the static and frequency-dependent dielectric function ε(ω) of nonmetallic crystals. We show that a real-space description becomes feasible for crystals by using a combination of a lattice-periodic (microscopic) scalar potential with a uniform (macroscopic) electric field as perturbation in a periodic structure calculation. The induced density and microscopic potential can be obtained self-consistently for fixed macroscopic field by using linear response theory in which Coulomb interactions and exchange-correlation effects are included. We use an iterative scheme, in which density and potential are updated in every cycle. The explicit evaluation of Kohn–Sham response kernels is avoided and their singular behavior as function of the frequency is treated analytically. Coulomb integrals are evaluated efficiently using auxiliary fitfunctions and we apply a screening technique for the lattice sums. The dielectric function can then be obtained from the induced current. We obtained ε(ω) for C, Si, and GaAs within the adiabatic local density approximation in good agreement with experiment. In particular in the low-frequency range no adjustment of the local density approximation (LDA) band gap seems to be necessary. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481315
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  • 7
    Electronic Resource
    Electronic Resource
    Relativistic total energy using regular approximations (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9783-9792 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we will discuss relativistic total energies using the zeroth order regular approximation (ZORA). A simple scaling of the ZORA one-electron Hamiltonian is shown to yield energies for the hydrogenlike atom that are exactly equal to the Dirac energies. The regular approximation is not gauge invariant in each order, but the scaled ZORA energy can be shown to be exactly gauge invariant for hydrogenic ions. It is practically gauge invariant for many-electron systems and proves superior to the (unscaled) first order regular approximation for atomic ionization energies. The regular approximation, if scaled, can therefore be applied already in zeroth order to molecular bond energies. Scalar relativistic density functional all-electron and frozen core calculations on diatomics, consisting of copper, silver, and gold and their hydrides are presented. We used exchange-correlation energy functionals commonly used in nonrelativistic calculations; both in the local-density approximation (LDA) and including density-gradient ("nonlocal'') corrections (NLDA). At the NLDA level the calculated dissociation energies are all within 0.2 eV from experiment, with an average of 0.1 eV. All-electron calculations for Au2 and AuH gave results within 0.05 eV of the frozen core calculations. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467943
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  • 8
    Electronic Resource
    Electronic Resource
    Performance of close-coupled wave packet methods for molecule-corrugated surface scattering (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5121-5136 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The H2+LiF(001) system was used to investigate the performance of the hybrid close-coupling wave packet (CCWP) method and of a symmetry adapted, fully close-coupled wave packet (SAWP) method for a molecule–surface problem characterized by fairly high corrugation. In the calculations, a realistic, φ-dependent model potential was used. The calculations were performed for a collision energy of 0.2 eV, with H2 initially in its j=0 rotational state at normal incidence to the surface. Large increases in the computational efficiencies of both wave packet methods were achieved by taking advantage of the potential coupling matrices associated with both methods becoming sparser with increasing molecule–surface distance. For the present model problem and employing this increased sparseness at longer range, the SAWP method is faster than the CCWP method by a factor of 2. The potential usefulness of the SAWP method for dissociative chemisorption problems is discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470599
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  • 9
    Electronic Resource
    Electronic Resource
    Performance of a fully close-coupled wave packet method for the H2+LiF(001) model problem (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 5512-5524 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have investigated the performance of a fully close-coupled wave packet method and its symmetry-adapted version for a model problem of H2 scattering from LiF(001). The computational cost of the fully close-coupled methods scales linearly with the number of rotation-diffraction states present in the basis set, provided that the sparseness of the potential coupling matrix is taken into account. For normal incidence, the symmetry adapted version is faster than the conventional close-coupling wave packet method by almost an order of magnitude. An extension of the method to more realistic molecule-surface problems is considered. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469281
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  • 10
    Electronic Resource
    Electronic Resource
    Parity-Resolved Rotationally Inelastic Collisions of Hexapole State-Selected NO (2.PI.1/2, J = 1/2-) with Ar (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 15573-15579 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100042a036
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