ion in the NH3+ IH20 system. 34 The D2 molecule can interact directly with the electron density on the nitrogen in this configuration. Other configurations such as the above but with the D2 rotated by 90· or an in-plane approach appear less favorable. Ab initio and semiempirical calculations of portions of the NH/ potential energy surface indicate that the above configuration represents a minim...

A satisfactory account of the van der Waals (London dispersion) forces is, in general, not possible by the Kohn-Sham method using standard local, semi-local GGA or meta-GGA density functionals. The recently proposed range-separated hybrid (RSH) approach, supplemented by second order perturbational corrections (MP2) to include long range dynamic correlation effects offers a physically consistent...

The conformational preferences of benznidazole were examined through the application of DFT, PCM and QTAIM calculations, whose results were compared with crystallography data. The geometries were fully optimized with minimum potential energy surface by means of the Relaxed Potential Energy Surface Scan (RPESS) at AM1, followed by the B3LYP/6-311++G(d,p) theoretical level. As a result, the s-cis...

New nine-dimensional (9D), ab initio electric dipole moment surfaces (DMSs) of methane in its ground electronic state are presented. The DMSs are computed using an explicitly correlated coupled cluster CCSD(T)-F12 method in conjunction with an F12-optimized correlation consistent basis set of the TZfamily. A symmetrized molecular bond representation is used to parameterise these 9D DMSs in term...

The results of a 5D ab initio quantum dynamical study of the vinylidene acetylene isomerization reaction are presented. The study is based on a new ab initio potential energy surface for the planar system, obtained with the CCSD(T) method and the cc-pVTZ basis set. The dynamics is studied with grid methods, using 4-atom Jacobi-like coordinates and wave packet propagation techniques. The results...

It is demonstrated that the Schrödinger operator in Ĥ | ψk >= Ek | ψk > can be associated with a covariance matrix whose eigenvalues are the squares of the spectrum σ(Ĥ + Iζ) where ζ is an arbitrarily chosen shift. An efficient method for extracting σ(Ĥ) components, in the vicinity of ζ, from a few specially selected eigenvectors of the inverse of the covariance matrix is derived. The method en...

Adiabatic representation Representation in which the electronic wave functions are calculated for fixed (i.e., nonmoving) nuclei. Avoided intersection Case in which two potential energy surfaces come together but do not intersect. Conical intersection Case in which two potential energy surfaces intersect such that their separation decreases to zero linearly in the relevant nuclear coordinates. ...

It is well known that positrons can live long enough to form complexes with atoms. The theoretical study of these complexes is important to interpret experimental data from both positron scattering by atoms and molecules and positron annihilation spectroscopy. There are typically two different kinds of positron complexes. In one of them a positron attaches to a neutral or ionic atom or molecule...

The Born-Oppenheimer separation of the Schroedinger equation allows the electronic and nuclear motions to be solved in three steps. 1) The solution of the electronic wave function at a discrete set of molecular conformations; 2) the fitting of this discrete set of energy values in order to construct an analytical approximation to the potential energy surface (PES) at all molecular conformations...

Laser pulse-induced photodissociation of molecules in rare-gas solids is investigated by representative quantum wavepackets or classical trajectories which are directed towards, or away from, cage exits, yielding dominant photodissociation into different neighbouring cages. The directionality is determined by a sequence of reflections inside the relief provided by the slopes of the potential en...