The lattice cluster theory (LCT) for the thermodynamics of polymer systems has recently been reformulated to treat strongly interacting self-assembling polymers composed of fully flexible linear telechelic chains [J. Dudowicz and K. F. Freed, J. Chem. Phys. 136, 064902 (2012)]. Here, we further extend the LCT for linear telechelic polymer melts to include a description of chain semiflexibility,...

Due to the severe self-interaction errors associated with some density functional approximations, conventional density functionals often fail to dissociate the hemibonded structure of the water dimer radical cation (H(2)O)(2)(+) into the correct fragments: H(2)O and H(2)O(+). Consequently, the binding energy of the hemibonded structure (H(2)O)(2)(+) is not well-defined. For a comprehensive comp...

We demonstrate that the recently developed extended multi-state complete active space second-order perturbation theory (XMS-CASPT2) [Shiozaki et al., J. Chem. Phys., 2011, 135, 081106] provides qualitatively correct potential energy surfaces for low-lying excited singlet states of pyrazine, while the potential energy surfaces of the standard MS-CASPT2 methods are ill-behaved near the crossing p...

High level ab initio methods have been used to calculate values of the quadrupole moment of the ground X (1)Sigmag+ state of N2 on a dense radial mesh spanning the interval of 0.8-12.1 a.u. Detailed convergence tests indicate that the resulting equilibrium values of the quadrupole moment Theta(e)=-1.1273 a.u. and its first radial derivative dTheta(R)/dR/e=0.9604 a.u. have absolute uncertainties...

We derive an exact representation of the exchange-correlation energy within density functional theory (DFT) which spawns a class of approximations leading to correct long-range asymptotic behavior. Using a simple approximation, we develop an electronic structure theory that combines a new local correlation energy (based on Monte Carlo calculations applied to the homogeneous electron gas) and a ...