Full configuration interaction potential energy curves for breaking bonds to hydrogen: An assessment of single-reference correlation methods

Several approximate correlation methods have been assessed for bond breaking reactions in BH, HF, and CH4 by comparison to the full configuration interaction limit. Second-order Møller–Plesset perturbation theory, coupled-cluster singles and doubles ~CCSD!, coupled-cluster with perturbative triples @CCSD~T!#, and the hybrid density-functional method Becke three parameter Lee–Yang– Parr have been considered. Both restricted and unrestricted references have been used along with the basis sets aug-cc-pVQZ, 6-31G**, and 6-31G* for BH, HF, and CH4 respectively. Among the methods considered, unrestricted CCSD and CCSD~T! provide potential energy curves which are the most parallel to the benchmark full CI curves, but the nonparallelity errors are fairly large ~up to 6 and 4 kcal mol, respectively!. Optimized-orbital coupled-cluster methods provide superior results but nevertheless exhibit approximately the same maximum errors. © 2003 American Institute of Physics. @DOI: 10.1063/1.1531658#