CCSD(T) expectation value calculations of first-order properties |
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Authors: | Miroslav Medveď Miroslav Urban Jozef Noga |
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Affiliation: | (1) Department of Chemistry, Faculty of Science, Matej Bel University, Tajovského 40, SK-97400 Banská Bystrica, Slovakia, XX;(2) Department of Physical Chemistry, Faculty of Science, Comenius University, Mlynská Dolina, SK-84215 Bratislava, Slovakia, XX;(3) Institute of Inorganic Chemistry, Slovak Academy of Sciences, SK-84236 Bratislava, Slovakia, XX |
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Abstract: | An expectation value approach to calculations of first-order properties using the non-iterative, triple-excitation amplitudes in the coupled cluster wave function is exploited. Three methods are suggested and analysed using the many body perturbation theory (MBPT) expansion arguments. The first method, in which non-iterative triple-excitation amplitudes are used in the expression for the expectation values, makes the wave function accurate through the second order of MBPT. In the second method, which is an extension of the first, effects of triple-excitation amplitudes are coupled with single- and double-excitation amplitudes. The correlated density matrix equivalent through the fourth order to that obtained when CCSDT-la amplitudes are used is employed in the third method. The suggested methods are tested on dipole moment and polarizability calculations for several diatomic closed-shell molecules and are compared to other related approaches. Received: 15 May 1997 / Accepted: 5 June 1997 |
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Keywords: | : CCSD(T) expectation value calculations First-order properties |
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