A direct generalized Bloch approach: ground and excited states of C 2

Abstract

In this study, the direct iterative algorithm for solving the generalized Bloch equation [J. Chem. Phys. 113 (2000) 2594], referred to as DGB approach, is applied to the C 2 molecule. The one-determinantal (1D), respectively, two-determinantal state-specific or state-selective (2D SS) version of the DGB approach is used to calculate the potential energy curves for the singlet ground state X 1 Σ g + and the first three excited states a 3Π u, b 3 Σ g − , and A 1Π u. To assess the performance of the DGB method, both correlation-consistent polarized-valence double zeta (cc-pVDZ) and triple zeta (cc-pVTZ) basis sets of Gaussian-type orbitals (GTOs) are employed. Beside these GTO bases, new Slater-type orbital (STO) basis sets are also examined for both the ground and excited states of the C 2 molecule. To compare the effectiveness of the STO and GTO bases, especially in the neighborhood of the equilibrium geometry, the spectroscopic constants are calculated and compared with the available experimental data. A good agreement of computed and experimental data is found, particularly when the STO double zeta basis is employed.