Multiscale quantum simulations applications

This section describes the main methodological advances that will be used in subsequent selected applications, including (1) Development of fast semiempirical methods for multiscale quantum simulations, (2) Directions for development of next-generation QM/MM models, and (3) Linear-scaling electrostatic and generalized solvent boundary methods. 

The main purpose of quantum-chemical modeling in materials simulation is to obtain necessary input data for the subsequent calculations of thermodynamic and kinetic parameters required for the next steps of multiscale techniques. Quantum-chemical calculations can also be used to predict various physical and chemical properties of the material in hand (the growing film in our case). Under quantum-chemical, we mean here both molecular and solid-state techniques, which are now implemented in numerous computer codes (such as Gaussian [25], GAMESS [26], or NWCHEM [27] for molecular applications and VASP [28], CASTEP [29], or ABINIT [30] for solid-state applications). 

The development of multiscale simulation techniques that involve the atomistic modeling of various structures and processes still remains at its early stage. There are many problems to be solved associated with more accurate and detailed description of these structures and processes. These problems include the development of efficient and fast methods for quantum calculations at the atomistic level, the development of transferable interatomic potentials (especially, reactive potentials) for molecular dynamic simulations, and the development of strategies for the application of multiscale simulation methods to other important processes and materials (optical, magnetic, sensing, etc.). 

A widely used type of multiscale simulation combines quantum mechanical and molecular mechanical (QM/MM) simulations. In this approach, the functional core of the molecular system, for example, the catalytic sites of an enzyme, is described at the electronic level (QM region), whereas the surrounding macromolecular system is treated using a classical description (MM region). Some of the biological applications for which QM/MM calculations have been widely utilized are chemical reactions in enzymes, proton transfer in proteins and optical excitations. In QM/MM... 

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