Properties of phosphorus compounds by density functional theory: CH3P species as a test case

Abstract

A comparison of different density functional theory (DFT) and molecular orbital (MO) methods for calculating molecular and energetic properties of low-coordinated phosphorus compounds is reported. While DFT methods include both Becke–Lee–Yang–Parr (BLYP and B3LYP) nonlocal functionals, MO methods involve second-order perturbation theory (MP2), quadratic configuration interaction [QCISD(T)], and coupled-cluster theory [CCSD(T)], in conjunction with the 6-31G(d,p), 6-311++G(3df,2p), and 6-311++G(3df,3pd) basis sets. Properties examined include geometrical parameters of the different CH3P equilibrium structures (phosphaethene, phosphinocarbene, methylphosphinidene, and a phosphacarbyne) and relevant transition structures for isomerisations and rearrangements in both the lowest-lying singlet and triplet states, vibrational wave numbers, relative energies, barrier heights, and singlet–triplet energy gaps. In addition, the heat of formation, ionization energy, and proton affinity of phosphaethene are also evaluated. Overall, the B3LYP method, when employed with a large basis set, yields energetic results comparable to the CCSD(T) results. Nevertheless, both DFT methods fail to predict the behavior of the addition/elimination reactions of the hydrogen atom in the triplet state.