First row benchmark tests of the parametrized configuration interaction with parameter X (PCI-X) scheme

Abstract

Articles you may be interested inComparisons of results from parametrized configuration interaction (PCI80) and from hybrid density functional theory with experiments for first row transition metal compounds A recently suggested scheme termed parametrized configuration interaction with parameter X ͑PCI-X͒ for scaling the correlation energy has been applied on a benchmark test consisting of 32 first row molecules. Several different methods like Mo "ller-Plesset second-order perturbation theory ͑MP2͒, modified coupled pair functional method ͑MCPF͒, averaged coupled pair functional method ͑ACPF͒, coupled cluster singles and doubles ͑CCSD͒, and CCSD with a perturbational estimate of triple excitations ͓CCSD͑T͔͒ have been tested using systematically chosen basis sets ranging from double zeta ͑DZ͒ to very large atomic natural orbital ͑ANO͒ sets containing several sets of d and f functions. For each method and basis set the scaling parameter is optimized. The scaling does in all cases lead to large, sometimes dramatic, improvements of the results. Typically, using a single reference state method like MCPF the average absolute deviation compared to experiments for the benchmark goes from an unscaled value of about 20 kcal/mol down to about 2 kcal/mol. For MCPF and similar methods no improvement of the results is obtained going beyond the DZϩpolarization ͑DZP͒ level. Significant improvements due to scaling occurs even at the highest level using the CCSD͑T͒ method and the largest basis set. For medium size basis sets the present scaling is far superior to the extrapolation schemes used in the Gaussian-1 and -2 ͑G1 and G2͒ theories.

An examination of intrinsic errors in electronic structure methods using the Environmental Molecular Sciences Laboratory computational results database and the Gaussian-2 set

“…44,[57][58][59][60] Their CBS limits, based on calculations up through cc-pV6Z or aug-cc-pV5Z are 76.3 and 76.5 kcal/ mol, respectively, with the RCCSD͑T͒ method. The Cl values, corrected for the effects of unlinked clusters, 6 were 75.7 and 75.8 kcal/mol with the same two basis set sequences. Core/valence correlation had minimal effect on the computed binding energy.…”

“…For example, Bauschlicher and Partridge 5 recently proposed a modification of the G2 theory that involves density functional and CCSD͑T͒ components. The parametrized configuration interaction scheme of Siegbahn et al, 6 which applies a multiplicative correction factor for the correlation contribution to the energy, was developed with the help of the G1 molecule set. Petersson and co-workers 7,8 have also compared the quality of their complete basis set models against the G2 set.…”

Calculating Bond Strengths for Transition-Metal Complexes

“…Instead, another parametrized ab initio based scheme will be the focus of most comparisons made here. This is the parametrized configuration interaction method with parameter 80 (PCI-80) scheme (6,7). This scheme has a single multiplicative empirical parameter based on the fraction of the correlation energy that is calculated using a partic ular method and basis set.…”

On Ethylene Polymerisation with Aluminium and Scandium Complexes: DFT and Post‐HF Calculations

“…). Moreover, it is known25 that CCSD(T) calculations using a double‐zeta quality basis set still yield energies with large absolute deviations from the true values as obtained using large, converged, basis sets. Using CCSD(T) with a double‐zeta quality basis set may yield energy barriers (as reported here) which are high by up to a factor of two 26.…”