Fock space coupled-cluster method for potential energy curves of KH and its cation

Abstract

Abstract A multireference Fock space (FS) coupled-cluster (CC) method formulated in the (2,0) sector and an equation-of-motion CC method for a single electron attachment (equivalent to (1,0) sector of FS) are employed to investigate potential energy curves (PECs) and spectroscopic characteristics for the KH molecule and its molecular cation. The calculations were carried out at the single and double excitation levels (CCSDs) using the intermediate Hamiltonian formalism. For both approaches the adopted reference state is a doubly ionized molecular cation KH2+. Such computational strategy has a concrete advantage for the calculations of PECs since the doubly positive ion dissociates into closed shell fragments; hence, the restricted Hartree-Fock (RHF) reference can be used over the whole range of interatomic distances. Results obtained (PECs and selected molecular constants) demonstrate that a first principles method can provide reliable theoretical data with an accuracy comparable or better than those generated by effective or model potentials containing adjustable empirical parameters.