Theoretical study of the TiC molecule: clarification of the ground state

Abstract

The electronic structure of the TiC molecule was examined using three types of multi-reference single- and double-excitation configuration interaction (MRSDCI) calculations with highly extended basis sets. Multi-reference coupled pair approximation (MRCPA) was applied after the MRSDCI calculations that included core—valence and core—core correlation in addition to the valence correlation (v-c-c CI). From the results of the most accurate calculation with MRCPA (v-c-c CPA) it was concluded that a 1Σ+ state is the ground state, despite previous calculations that suggested a 3Σ+ state with a 1Σ+ state lying only slightly above it. The 1Σ+ state is more highly correlated than the 3Σ+ state, and it was found that use of a size-consistent method is necessary to predict the relative stability accurately. The study evaluated the spectroscopic constants and considered the effect of the core (Ti 3p) correlation on these parameters. By taking the core correlation effect into account, the estimation of the dissociation energy (D e) was improved dramatically; D e obtained through v-c-c CPA was 4.457eV for the 1Σ+ ground state, which agrees well with the experimental value (the latest being 4.35 ± 0.31 eV).