The charge distribution in the water molecule has been analyzed using a broad variety of basis sets, four different quantum mechanical methods (Hartree-Fock, Becke3LYP, MP2, and QCISD), and six population analysis methods (Mulliken, NPA, AIM, CHELPG, Merz-Kollman, and Resp). The influence of the molecular structure on the calculated atomic charges has been studied using small perturbations of t...

An embedded cluster approach was applied to study the electronic excitations on the NiO~001! surface. Using a quantum chemical calculation, a small (NiO5) 82 cluster was embedded in a set of point charges to model the NiO~001! surface. Starting from the unrestricted Hartree-Fock level of theory, we calculate the ground-state properties to provide some insight into electronic structure and excit...

The effects have been studied of mono- and dibenzannulation of a benzyl radical with hybrid density functional theory (B3LYP) and quadratic configuration interaction theory (QCISD). Bond dissociation energies and enthalpies are reported that were determined at the common level QCISD/6-311G**//B3LYP/6-31G* for the benzylic C-H bonds of toluene 1H, the monobenzannulated polycyclic aromatic hydroc...

All-electron CCSD(T), QCISD(T) and MP4(SDQ) calculations including relativistic effects via the use of the IORAmm Hamiltonian have been performed for PdCO. The optimized molecular geometry is in nice agreement with the recently obtained experimental data. The Pd–CO bond dissociation energy is estimated to be 38.8 kcal/mol. The vibrational spectrum of PdCO is calculated and a reassessment of the...

Three new multicoefficient correlation methods (MCCMs) called BMC-QCISD, BMC-CCSD, and BMC-CCSD-C are optimized against 274 data that include atomization energies, electron affinities, ionization potentials, and reaction barrier heights. A new basis set called 6-31B(d) is developed and used as part of the new methods. BMC-QCISD has mean unsigned errors in calculating atomization energies per bo...

The effect of counterions on the bonding, stability and aromaticity of trigonal dianion metal clusters has been analyzed through the behavior of various conceptual density functional theory based reactivity descriptors and the nucleus independent chemical shift calculated at different levels of theory, comprising one-determinant approaches and beyond (QCISD, CASSCF(8,8) and NEVPT2), for a prope...

The excitation energies and ionization potentials of the atoms in the first transition series are notoriously difficult to compute accurately. Errors in calculated excitation energies can range from 1–4 eV at the Hartree-Fock level, and errors as high as 1.5eV are encountered for ionization energies. In the current work we present and discuss the results of a systematic study of the first trans...

The energy difference between the linear S+ and cyclic £?2 structures of G$ has been investigated using large [5s3p2dlf] basis sets and multireference electron correlation treatments, including complete active space SCF (CASSCF), multireference CI (MRCI), and averaged coupled-pair functional (ACPF) methods, as well as the single-reference quadratic configuration interaction (QCISD(T)) method. O...