title: Theoretical investigation of the alkaline-earth dihydrides from relativistic all-electron, pseudopotential, and density-functional study.
abstract: Highly precise ground state geometries, harmonic vibrational frequencies and force constants of alkaline-earth dihydrides from CaH2 to RaH2 are obtained using relativistic small-core energy-consistent effective core potentials at the coupled-cluster level. The results are compared with all-electron as well as density functional calculations. All-electron results, in particular, clearly show the importance of relativistic effects in the properties considered in this paper. The monotonic trends in the geometries are explained in terms of second-order perturbation theory. Trends in the force constants are monotonic except for the bending mode where an anomaly occurs from BaH2 to RaH2. It is rationalized in terms of reduced s-d hybridization due to relativity, which is shown to be an energy effect attributed to the stabilization of the s orbital. The pseudopotentials show an excellent performance in comparison with all-electron methods and are therefore successfully transferred to molecular cases. The density functional methods, however, suffer from functional dependencies with B3LYP performing the best in this case.
authors.affiliation: Quantum and Computational Chemistry Laboratory, Department of Chemistry, School of Molecular Science (BK21), KAIST, 373-1 Guseong-dong, Yuseong-gu, Daejoen 305-701, Korea.
authors.forename: Ivan S
authors.initials: IS
authors.lastname: Lim
authors.forename: Yoon Sup
authors.initials: YS
authors.lastname: Lee