Dipole moments calculations of transition metal mononitrides: ScN, TiN, VN, and CrN: Limits of the CCSD(T) method

摘要

Coupled-cluster calculations of selected molecular properties of ScN, TiN, VN, and CrN in their ground states are presented. It is shown that the single determinant reference Restricted Open Shell Hartree-Fock Coupled Clusters Singles Doubles noniterative Triples (ROHF-CCSD(T)) method provides reasonably accurate bond distances, harmonic frequencies, and most dipole moments of these molecules but fails to predict sufficiently accurate dipole moment of CrN. The reason for the low accuracy in obtaining the dipole moment of CrN is analyzed and is attributed to the presence of the series of large single excitation CC amplitudes. This affects the correct response of the molecular CC wavefunction to the external field. Quasirelativistic effects are considered using the Massvelocity-Darwin correction. Changes of dipole moments due to relativity are stressed, and trends throughout the series of molecules are analyzed using their bonding characteristics. (C) 2002 Wiley Periodicals, Inc. [References: 49]