Ab initio MRSDCI study on the low-lying electronic states of the lithium chloride molecule (LiCl).

Potential energy curves (PECs) for the low-lying states of the lithium chloride molecule (LiCl) have been calculated using the internally contracted multireference single- and double-excitation configuration interaction (MRSDCI) method with the aug-cc-PVnZ (AVnZ) and aug-cc-PCVnZ (ACVnZ) basis sets, where n = T, Q, and 5. First, we calculate PECs for 7 spin-orbit (SO)-free Λ-S states, X(1)Σ(+), A(1)Σ(+), (3)Σ(+), (1)Π, and (3)Π, and then obtain PECs for 13 SO Ω states, X0(+), A0(+), B0(+), 0(-)(I), 0(-)(II), 1(I), 1(II), 1(III), and 2, by diagonalizing the matrix of the electronic Hamiltonian plus the Breit-Pauli SO Hamiltonian. The MRSDCI calculations not including core orbital correlation through the single and double excitations are also performed with the AV5Z and ACV5Z basis sets. The Davidson corrections (Q0) are added to both the Λ-S and Ω state energies. Vibrational eigenstates for the obtained X(1)Σ(+) and X0(+) PECs are calculated by solving the time-independent Schrödinger equation with the grid method. Thus, the effects of basis set, core orbital correlation, and the Davidson correction on the X(1)Σ(+) and X0(+) PECs of LiCl are investigated by comparing the spectroscopic constants calculated from the PECs with one another and with experiment. It is confirmed that to accurately predict the spectroscopic constants we need to include core-electron correlation in the CI expansion and use the basis sets designed to describe core-valence correlation, i.e., ACVnZ. The SO PECs presented in this paper will be of help in the future study of diatomic alkali halide dynamics.