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- Lopez Cacheiro, Javier, et al.
(author)
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The CCSD(T) Model With Cholesky Decomposition of Orbital Energy Denominators
- 2011
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In: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608. ; 111:2, s. 349-355
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Journal article (peer-reviewed)abstract
- A new implementation of the coupled cluster singles and doubles with approximate triples correction method [CCSD(T)] using Cholesky decomposition of the orbital energy denominators is described. The new algorithm reduces the scaling of CCSD(T) from N-7 to N-6, where N is the number of orbitals. The Cholesky decomposition is carried out using simple analytical expressions that allow us to evaluate a priori the order in which the decomposition should be carried out and to obtain the relevant parts of the vectors whenever needed in the calculation. Several benchmarks have been carried out comparing the performance of the conventional and Cholesky CCSD(T) implementations. The Cholesky implementation shows a speed-up factor larger than O-2/V, where O is the number of occupied and V the number of virtual orbitals, and in general at most 5 vectors are needed to get a precision of mu E-h. We demonstrate that the Cholesky algorithm is better suited for studying large systems. (c) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 349-355, 2011
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| 2. |
- Lopez Cacheiro, Javier, et al.
(author)
-
Theoretical pressure and dielectric second virial coefficients of CO-Ar
- 2008
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In: Molecular Physics. - : Informa UK Limited. - 1362-3028 .- 0026-8976. ; 106:7, s. 881-892
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Journal article (peer-reviewed)abstract
- Using coupled cluster singles and doubles linear response theory and the d-aug-cc-pVTZ basis set extended with a 3s3p2d1f1g set of midbond functions, the interaction induced electric dipole polarisability surface of the CO-Ar van der Waals complex is computed. Combining this surface with accurate intermolecular potential energy and electric dipole surfaces, the pressure and dielectric second virial coefficients of the complex are calculated by a classical statistical approach. Excellent agreement with experimental results (to within the experimental error bars) is obtained for the pressure second virial coefficient over a range of temperatures. No previous experimental or theoretical investigations have been carried out for the dielectric second virial coefficient, B-epsilon(T), which is estimated to be about 1.9 cm(6) mol(-1) at room temperature. This value results from a balance of terms due to the interaction induced electric dipole polarisability (predominant at high temperatures) and orientational electric dipole contributions.
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