Nuclear geometry perturbations

Moreover, for the observables depending on external electric field, its specific effect has to be investigated the electric field induces new terms in the nuclear Hamiltonian, due to the change of equilibrium geometry and the nuclear motion perturbation. Pandey and Santry (14) has brought to the fore this effect and calculated the correction which only concerns the parallel component. It is represented by the following expression ... 

Although FEP is mostly useful for binding type of simulations rather than chemical reactions, it can be valuable for reduction potential and pKa calculations, which are of interest from many perspectives. For example, prediction of reliable pKa values of key groups can be used as a criterion for establishing a reliable microscopic model for complex systems. Technically, FEP calculation with QM/MM potentials is complicated by the fact that QM potentials are non-seperable [78], When the species subject to perturbation (A B) differ mainly in electronic structure but similar in nuclear connectivity (e.g., an oxidation-reduction pair), we find it is beneficial to use the same set of nuclear geometry for the two states [78], i.e., the coupling potential function has the form,... 

The collision-assisted predissociation in iodine B O + state merits a detailed discussion. It is well known that B state is weakly coupled to the dissociative A 1m state by rotational and hyperfine-structure terms in the molecular Hamiltonian. The natural predissociation rate strongly depends on the vibrational quantum number (pronounced maxima for o=5 and u = 25, a minimum for u= 15), this dependence being due to a variation of the Franck-Condon factor. " The predissociation rate is enhanced by collisions. In absence of a detailed theoretical treatment of the colhsion-assisted 12 predissociation, one can suppose that the asymmetric perturbation (breakdown of the orbital symmetry) in the collisional complex affects electronic and rotational wavefimctions but does not change the nuclear geometry. 

Nuclear PSAs contain considerable uncertainty associated with the physical and chemical processes involved in core degradation, movement of the molten core in the reactor vessel, on the containment floor, and the response of the containment to the stresses placed upon it. The current models of these processes need refinement and validation. Because the geometry is greatly changed by small perturbations after degradation has commenced, it is not clear that the phenomcn.i can be treated. 

In this diabatic Schrodinger equation, the only terms that couple the nuclear wave functions Xd(R-/v) are the elements of the W RjJ and zd q%) matrices. The —(fi2/2p)W i(Rx) matrix does not have poles at conical intersection geometries [as opposed to W(2 ad(R>.) and furthermore it only appears as an additive term to the diabatic energy matrix cd(q>.) and does not increase the computational effort for the solution of Eq. (55). Since the neglected gradient term is expected to be small, it can be reintroduced as a first-order perturbation afterward, if desired. 

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