Enthalpies of formation of phosphorus and oxygen compounds determined by the correlation consistent composite approach

Abstract

AbstractThe heats of formation of small molecules (O2, O3, P2, P4, PO, PO2, PO3, P2O, P2O2, and P4O6) have been determined by a modified version of the correlation consistent composite approach (ccCA). The equilibrium geometries and vibrational frequencies were computed via density functional theory, using the M06‐2X exchange‐correlation functional and 6‐31G(2df,p) basis sets. The original methodology requires CCSD(T) energy, which now is obtained by CR‐CCSD(T)_L method. The theoretical heats of formation, whose accuracy is estimated as ranging from ±4 to ±10 kJ mol−1, are closer to the available experimental data, but O3 and P4O6 are exceptions, exceed the desired value of ±10 kJ mol−1. The ccCA result for ozone (159.2 kJ mol−1) shows a deviation in comparison to experimental data (142.67 ± 1.7 kJ mol−1), but it is closer to the calculated value 154.0 kJ mol−1 by the high‐level quantum chemical calculation (W1U; Janoschek and Fabian, J. Mol. Struct. 2006, 780–781, 80). The value of heat formation to P4O6 was estimated to be −1706.3 kJ mol−1. This value is quite different of experimental data, and additional studies are needed to understand this deviation. © 2012 Wiley Periodicals, Inc.