Implicit solvent methods

Continuum models can be directly interfaced with atomistic or coarse grain models using a two-way embedded interface. In this scheme, the atomistic or CG model is embedded within a continuum model. Implicit solvent methods, in which an atomistic or CG model of a solute is embedded within a continuum model of the solvent, are popular and well-established examples of this type of interface. Implicit solvent models represent the solvent as a dielectric continuum, and allow the electrostatics of the atomistic or CG solute to polarise the continuum, which then results in an electrostatic reaction field that returns to interact with the solute. Implicit solvent models have been reviewed in detail many times before, and enable the dynamic transfer of electrostatic information across the atomistic/ continuum or CG/continuum interfaces. Recently, new multiscale continuum methods have been developed that allow for the dynamic transfer of mechanical and hydrodynamic information across these interfaces. One example is the work by Villa... 

Lee, M.S., Salsbury, F.R., Olson, M.A. An efficient hybrid explicit/implicit solvent method for biomolecular simulations. J. Comput. Chem. 2004,25(16), 1967-78, December. 

As mentioned, implicit solvent methods are approximations designed to simplify the description of the aqueous environment around molecules and thereby reduce the degrees of freedom in a simulation. This section outlines the various methods by which solvent-mediated polar and apolar interactions are described in an implicit solvent setting. 

Although numerous methods exist for computing polar interactions in an implicit solvent setting, this section gives only a brief overview of some of the most popular methods available. Interested readers should refer to the reviews by Simonson and Roux for a more comprehensive overview of available implicit solvent methods. 

However, the field is far from being established, and further developments are required, especially in order to extend the time-independent treatment to large macromolecular systems in the condensed phase or to allow for reliable studies in case some part of the vibrational problem is related to highly anharmonic PESs involving large-amplitude motions or solvent librations. There, use of effective QM/ MM schemes combined with implicit solvent methods would probably represent a viable choice to reduce the computational cost of otherwise prohibitively expensive anharmonic frequency analysis. Another field where the potentialities of time-independent approaches have not yet been fully assessed is that of ultrafast vibrational spectroscopies, whose interest has enormously increased in the last years, due to their... 

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