Nuclear-electron attraction, electronic structure calculations

The fact that the calculation of Ee as well as of its derivatives with respect to nuclear coordinates with accurate electronic-structure methods is non-trivial and often time-consuming, makes the use of simpler, parameterized methods attractive, in particular when studying larger systems of low symmetry and/or studying (very) many structures (which easily is the case when attempting to optimize the structure). With these, the total energy is given as some analytical or numerical function of the nuclear coordinates and atom types, i.e.,... 

Theoretical methods that combine ab initio MD on the fly with the Wigner distribution approach, which is based on classical treatment of nuclei and on quantum chemical treatment of electronic structure, represent an important theoretical tool for the analysis and control of ultrashort processes in complex systems. Moreover, the possibility to include, in principle, quantum effects for nuclear motion by introducing appropriate corrections makes this approach attractive for further developments. However, for this purpose, new proposals for improving the efficient inclusion of quantum effects for the motion of nuclei and fast but accurate calculations of MD on the fly in the electronic excited states are mandatory. Both aspects represent attractive and important theoretical research areas for the future. 

As an example for an open-shell system, we carried out calculations for Th2. Th clusters have been attracting increasing attention due to potential nuclear energy applications. The calculated structural, electronic structure and energetic properties are summarized in Table 2. We have identified three low-lying electronic states without spin-orbit interactions, the sa dn da db sa g, sa dn da sa X, and sa dn sa 11+ states. 

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