Symmetry-adapted formulation of the combined G-particle-hole hypervirial equation and Hermitian operator method

DIEGO R. ALCOBA; GUSTAVO E. MASSACCESI; OFELIA B. OÑA; JUAN J. TORRES; LUIS LAIN; ALICIA TORRE

JOURNAL OF MATHEMATICAL CHEMISTRY

SPRINGER

Lugar: Berlin; Año: 2014 vol. 52 p. 1794 - 1806

0259-9791

High accuracy energies of low-lying excited states, in molecular systems, have been determined by means of a procedure which combines the G-particle-hole hypervirial (GHV) equation method (Alcoba et al. in Int J Quantum Chem 109:3178, 2009) and the Hermitian operator (HO) one (Bouten et al. in Nucl Phys A 202:127, 1973). This work reports a suitable strategy to introduce the point group symmetry within the framework of the combined GHV-HO method, which leads to an improvement of the computational efficiency. The resulting symmetry-adapted formulation has been applied to illustrate the computer timings and the hardware requirements in selected chemical systems of several geometries. The new formulation is used to study the low-lying excited states torsional potentials in the ethylene molecule.