The effect of hydration on the vertical ionization energy (VIE) of thymine was characterized using equation-of-motion ionization potential coupled-cluster (EOM-IP-CCSD) and effective fragment potential (EFP) methods. We considered several microsolvated clusters as well as thymine solvated in bulk water. The VIE in bulk water was computed by averaging over solvent-solute configurations obtained ...

To understand the performance of popular density-functional theory exchange-correlation (xc) functionals in simulations of liquid water, water monomers and dimers were extracted from a PBE simulation of liquid water and examined with coupled cluster with single and double excitations plus a perturbative correction for connected triples [CCSD(T)]. CCSD(T) reveals that most of the dimers are unbo...

Moller-Plesset second-order (MP2) perturbation theory remains the least expensive standard ab initio method that includes electron correlation, scaling as O(N5) with the number of molecular orbitals N. Unfortunately, when restricted Hartree-Fock orbitals are employed, the potential energy curves calculated with this method are of little use at large interatomic separations because of the diverg...

A set of 42 molecules with N-F, O-F, N-Cl, P-F, and As-F bonds has been investigated in the search for potential bond anomalies, which lead to reverse bond length-bond strength (BLBS) relationships. The intrinsic strength of each bond investigated has been determined by the local stretching force constant obtained at the CCSD(T)/aug-cc-pVTZ level of theory. N-F or O-F bond anomalies were found ...

The indirect nuclear spin–spin coupling constants of allene and of two sterically strained hydrocarbons – cyclopropane and cyclopropene – calculated at different levels of electronic-structure theory are compared with each other and with experimental equilibrium constants, obtained from experiment by subtracting calculated vibrational contributions. It is found that, even in a relatively small ...

To understand the performance of popular density-functional theory (DFT) exchange-correlation (xc) functionals in simulations of liquid water, water monomers and dimers were extracted from a PBE simulation of liquid water and examined with coupled cluster with single and double excitations plus a perturbative correction for connected triples [CCSD(T)]. CCSD(T) reveals that most of the dimers ar...

The structures of m-benzyne and its fluorinated derivative, tetrafluoro-m-benzyne, were investigated using coupled cluster methods including triple excitations [CCSD(T) and CCSDT], different reference wave functions (spin-restricted Hartree-Fock, spin-unrestricted Hartree-Fock, and Brueckner), and different basis sets [6-31G(d,p) and correlation-consistent valence triple-zeta (cc-pVTZ)]. The in...

The adsorption of Ag, Au, and Pd atoms on benzene, coronene, and graphene has been studied using post Hartree-Fock wave function theory (CCSD(T), MP2) and density functional theory (M06-2X, DFT-D3, PBE, vdW-DF) methods. The CCSD(T) benchmark binding energies for benzene-M (M = Pd, Au, Ag) complexes are 19.7, 4.2, and 2.3 kcal/mol, respectively. We found that the nature of binding of the three m...

A new hardware-agnostic contraction algorithm for tensors of arbitrary symmetry and sparsity is presented. The algorithm is implemented as a stand-alone open-source code libxm. This code is also integrated with general tensor library libtensor and with the Q-Chem quantum-chemistry package. An overview of the algorithm, its implementation, and benchmarks are presented. Similarly to other tensor ...