Molecular applications of multireference coupled-cluster methods using an incomplete model space: direct calculation of excitation energies

Pal, Sourav ; Rittby, Magnus ; Bartlett, Rodney J. ; Sinha, Dhiman ; Mukherjee, Debashis (1988) Molecular applications of multireference coupled-cluster methods using an incomplete model space: direct calculation of excitation energies Journal of Chemical Physics, 88 (7). pp. 4357-4366. ISSN 0021-9606

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Official URL: http://link.aip.org/link/JCPSA6/v88/i7/p4357/s1

Related URL: http://dx.doi.org/10.1063/1.453795

Abstract

A multireference coupled-cluster (MRCC) formulation for the direct calculation of excitation energies and ionization potentials is presented. The reference space connects a set of p-h excited determinants built from all the set of active particles and holes in the model space. This model space is incomplete, requiring a Fock-space approach and the postulate of a "universal" wave operator to arrive at a linked diagram expression for the effective Hamiltonian Heff, whose eigenvalues are the excitation energies for the problem. Use of a normal-ordered exponential cluster ansatz allows one to construct, hierarchically, the CC equations for the p-h model space starting from the ground state. We present an extension of an earlier formulation for excitation energies that allows us to have both active and inactive particles and holes in our method. Numerical applications are reported for the prototypical small molecules CO and N2.

Item Type:Article
Source:Copyright of this article belongs to American Institute of Physics.
ID Code:25913
Deposited On:04 Dec 2010 11:02
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