Coupled-cluster dynamic polarizabilities including triple excitations

Hammond, Jeff R.; de Jong, Wibe A.; Kowalski, Karol

doi:doi:10.1063/1.2929840

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New torsion potential expression for molecules without rotational symmetry

A new torsion potential function for bond rotations without rotational symmetry is proposed. This function is composed of a few Gaussian-type terms each corresponding to an eclipsed conformation of the 1,2 substituents of the C–C bonds. Different from the truncated Fourier series or the truncated cosine polynomial, it is easy to determine how many terms are needed to represent any type of torsion potential barrier at a glance using the Gaussian-type function. It could also intuitively deduce th...

Numerical integration of exchange-correlation energies and potentials using transformed sparse grids

A new numerical integration procedure for exchange-correlation energies and potentials is proposed and “proof of principle” results are presented. The numerical integration grids are built from sparse-tensor product grids (constructed according to Smolyak’s prescription [Dokl. Akad. Nauk. 4, 240 (1963)] ) on the unit cube. The grid on the unit cube is then transformed to a grid over real space with respect to a weight function, which we choose to be the promolecular density. This produces a “...

Dynamic polarizabilities for open- and closed-shell molecules were obtained by using coupled-cluster (CC) linear response theory with full treatment of singles, doubles, and triples (CCSDT-LR) with large basis sets utilizing the NWChem software suite. By using four approximate CC methods in conjunction with augmented cc-pVNZ basis sets, we are able to evaluate the convergence in both many-electron and one-electron spaces. For systems with primarily dynamic correlation, the results for CC3 and CCSDT are almost indistinguishable. For systems with significant static correlation, the CC3 tends to overestimate the triples contribution, while the PS(T) approximation [ J. Chem. Phys. 127, 164105 (2007) ] produces mixed results that are heavily dependent on the accuracies provided by noniterative approaches used to correct the equation-of-motion CCSD excitation energies. Our results for open-shell systems show that the choice of reference (restricted open-shell Hartree–Fock versus unrestricted Hartree–Fock) can have a significant impact on the accuracy of polarizabilities. A simple extrapolation based on pentuple-zeta CCSD calculations and triple-zeta CCSDT calculations reproduces experimental results with good precision in most cases.

Article Outline

INTRODUCTION
THEORY AND COMPUTATIONAL DETAILS
RESULTS
1. Ne and HF
2. N₂ and CO
3. CN and NO
4. O₂
CONCLUSIONS

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KEYWORDS and PACS

Keywords

coupled cluster calculations, excited states, HF calculations, polarisability

PACS

31.15.bw

Coupled-cluster theory
33.15.Kr

Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

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http://dx.doi.org/10.1063/1.2929840

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0021-9606 (print)

1089-7690 (online)

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American Institute of Physics

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