Coupled-Cluster Studies of HOONO~+:Additional Conformers of the ~2A'ON~+-OOH Complex and a Comparison of Restricted and Unrestricted Open-Shell Hartree-Fock Coupled-Cluster Results

摘要

Coupled-cluster calculations using the CCSD(T) method (coupled-cluster singles and doubles with perturbative inclusion of triple excitations) and correlation-consistent basis sets have been used to address aspects of the lowest ~2A' and ~2A" potential energy surfaces of the peroxynitrous acid cation (HOONO~+).First,searches were made for conformers of the ~2A" ON~+-OOH complex in addition to the cis-trans species previously located by the authors (J Chem Phys 2003,118,1721).Two conformers were located-namely,trans-cis and trans-trans species-and these were confirmed to be local minima.The trans-trans conformer was calculated to be less than 0.5 kcal mol~(-1) higher in energy than the cis-trans conformer,and the trans-cis conformer was calculated to be about 6.4 kcal mol~(-1) higher in energy than the cis-trans conformer.Second,comparisons were made between CCSD(T) results obtained with unrestricted Hartree-Fock (UHF) and restricted open-shell Hartree-Fock (ROHF) reference determinants.These comparisons were made on the ~2A" complexes and the planar ~2A' HOONO~+ stationary points.In general,the energy differences between UHF-CCSD(T) and ROHF-CCSD(T) were very small,and well within the error bars of the methods.