186,293 research outputs found
A closed-shell coupled-cluster treatment of the Breit--Paulifirst-order relativistic energy correction
No full textCalculation of electric dipole hypershieldings at the nuclei in the Hellmann-Feynman approximation
No full textThe third-rank electric hypershieldings at the nuclei were calculated at the Hartree-Fock level of theory in the Hellmann-Feynman approximation. It was shown that the nuclear electric hypershieldings are closely related to molecular vibrational absorption intensities. A generalization of the atomic polar tensors was proposed to rationalize these intensities. It was found that best results are obtained with the R12 and R12+ basis sets, designed for the calculation of electronic energies by the explicitly correlated R12 method
Hartree-Fock and Kohn-Sham time-dependent response theory in a second-quantization atomic-orbital formalism suitable for linear scaling
No full textWe present a second-quantization based atomic-orbital method for the computation of
time-dependent response functions within Hartree-Fock and Kohn-Sham density-functional
theories. The method is suited for linear scaling. Illustrative results are presented for excitation
energies, one- and two-photon transition moments, polarizabilities, and hyperpolarizabilities for
hexagonal BN sheets with up to 180 atoms
The equilibrium structure of ferrocene
No full textThe molecular structures of ferrocene in the eclipsed (equilibrium) and staggered (saddle-point) conformations have been determined by full geometry optimizations at the levels of second-order Møller–Plesset (MP2) theory, coupled-cluster singles-and-doubles (CCSD) theory and CCSD theory with a perturbative triples correction [CCSD(T)] in a TZV2P+f basis set. Existing experimental results are reviewed. The agreement between the CCSD(T) results and experiment is in all cases excellent; the calculated structure parameters and the barrier to internal rotation of the ligand rings differ from the most accurate experimental values by calculations for single-configuration-dominated transition metal complexes such as ferrocene thus appear to have an accuracy comparable to that observed for molecules containing only first- and second-row atoms, and to be of a quality similar to that obtained experimentally. A comparison with previous DFT results indicates that the B3LYP model gives overall the overall the best DFT results,
with a deviation of around 2 pm for the metal–carbon distance
and smaller errors for the cyclopentadienyl rings
DIRECT ATOMIC ORBITAL BASED SELF-CONSISTENT-FIELD CALCULATIONS OF NONLINEAR MOLECULAR-PROPERTIES - APPLICATION TO THE FREQUENCY-DEPENDENT HYPERPOLARIZABILITY OF PARA-NITROANILINE
No full text
Gauge-origin independent magneto optical activity withincoupled-cluster response theory
No full textWe present a gauge-origin independent formulation of the Faraday B term of magnetic circular dichroism and of the Verdet constant of magneto-optical rotation, in terms of first derivatives with respect to the magnetic field strength of gauge invariant coupled cluster response functionals [1]. Gauge invariance is ensured by the derivative formulation in connection with the use of a magnetic field dependent basis of atomic orbitals, the so-called London orbitals. To our knowledge this represent the first application of London atomic orbitals to the calculation of frequency dependent quadratic response properties. The approach can easily be extended to other wavefunction models, and to any other frequency dependent property which can be formulated as total derivative of a (frequency-dependent) functional with respect to the field strengths of a static magnetic perturbation. In other words, any properties for which the frequency dependence is not associated with the magnetic field. This is for example the case for the hypermagnetizabilities in the Cotton-Moutton effect. The implementation of the derived equations is currently undertaken for a CCSD wavefunction on a local version of the Dalton program.
[1] S. Coriani, C. Hättig, P. Jørgensen, T. Helgake
Efficient parallel implementation of response theory: Calculations of the second hyperpolarizability of polyacenes
No full textThe accuracy of ab initio molecular geometries for systems containingsecond-row atoms
No full textThe performance of the standard hierarchy of ab initio models—that is, Hartree–Fock theory,
second-order Møller–Plesset theory, coupled-cluster singles-and-doubles theory, and coupled-cluster
singles-doubles-approximate-triples theory—in combination with correlation-consistent basis sets is
investigated for equilibrium geometries of molecules containing second-row elements. From an
analysis on a collection of 31 molecules yielding statistical samples of 41 bond distances and 13
bond angles, the statistical errors mean deviation, mean absolute deviation, standard deviation, and
maximum absolute deviation are established at each level of theory. The importance of core
correlation is examined by comparing calculations in the frozen-core approximation with
calculations where all electrons are correlate
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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