Parameterization electronic structure methods

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.,... 

Bulutay studied the interaction between two larger, spherical Si clusters. He used an efficient parameterized electronic-structure method that can handle 10000s of atoms but could only treat electronic properties. The reduction of the symmetry from spherical to approximately ellipsoidal could be identified in the calculated optical properties, which in turn can be used experimentally to identify the aggregation of such systems. 

Using a parameterized electronic-structure method, Hasmy et studied theoretically the formation of such linear chains in break-junction experiments through molecular-dynamics simulations. They compared the three coinage elements, Cu, Ag, and Au, and found that in particular for Au longer linear chains could be formed before the breaking of the junction, whereas only shorter chains were found for the other elements. They ascribed this effect to sd orbital hybridization. 

The elementary empirical tool for the molecular modelling of polyatomic systems is the method of molecular mechanics (MM) [2,3]. It explicitly employs intuitively transparent features of molecular electronic structure like localization of chemical bonds and groups. The basic assumption of the MM is the possibility to directly parameterize molecular PES in the form of a sum of contributions (force fields) relevant to bonds, their interactions, and to interactions of non-bonded atoms ... 

During last decades the DFT based methods have received a wide circulation in calculations on TMCs electronic structure [34,85-88]. It is, first of all, due to widespread use of extended basis sets, allowing to improve the quality of the calculated electronic density, and, second, due to development of successful (so called - hybrid) parameterizations for the exchange-correlation functionals vide infra for discussion). It is generally believed, that the DFT-based methods give in case of TMCs more reliable results, than the HER non-empirical methods and that their accuracy is comparable to that which can be achieved after taking into account perturbation theory corrections to the HER at the MP2 or some limited Cl level [88-90]. 

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