An analytic scheme is presented for the evaluation of first derivatives of the energy for a unitary group based spin-adapted coupled cluster (CC) theory, namely, the combinatoric open-shell CC (COSCC) approach within the singles and doubles approximation. The widely used Lagrange multiplier approach is employed for the derivation of an analytical expression for the first derivative of the energy, which in combination with the well-established density-matrix formulation, is used for the computation of first-order electrical properties. Derivations of the spin-adapted lambda equations for determining the Lagrange multipliers and the expressions for the spin-free effective density matrices for the COSCC approach are presented. Orbital-relaxation effects due to the electric-field perturbation are treated via the Z-vector technique. We present calculations of the dipole moments for a number of doublet radicals in their ground states using restricted open-shell Hartree-Fock (ROHF) and quasi-restricted HF (QRHF) orbitals in order to demonstrate the applicability of our analytic scheme for computing energy derivatives. We also report calculations of the chlorine electric-field gradients and nuclear quadrupole-coupling constants for the CCl, CH2Cl, ClO2, and SiCl radicals.
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14 September 2014
Research Article|
September 08 2014
Analytic first derivatives for a spin-adapted open-shell coupled cluster theory: Evaluation of first-order electrical properties
Dipayan Datta;
Dipayan Datta
a)
Institut für Physikalische Chemie,
Johannes Gutenberg-Universität Mainz
, Duesbergweg 10-14, D-55128 Mainz, Germany
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Jürgen Gauss
Jürgen Gauss
b)
Institut für Physikalische Chemie,
Johannes Gutenberg-Universität Mainz
, Duesbergweg 10-14, D-55128 Mainz, Germany
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a)
Electronic mail: datta@uni-mainz.de
b)
Electronic mail: gauss@uni-mainz.de
J. Chem. Phys. 141, 104102 (2014)
Article history
Received:
July 16 2014
Accepted:
August 25 2014
Citation
Dipayan Datta, Jürgen Gauss; Analytic first derivatives for a spin-adapted open-shell coupled cluster theory: Evaluation of first-order electrical properties. J. Chem. Phys. 14 September 2014; 141 (10): 104102. https://doi.org/10.1063/1.4894773
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