Accelerating QM/MM Calculations by Using the Mean Field Approximation

It is well known that solvents can modify the frequency and intensity of the solute spectral bands, the thermodynamics and kinetics of chemical reactions, the strength of molecular interactions or the fate of solute excited states. The theoretical study of solvent effectsSolvent effects is quite complicated since the presence of the solvent introduces additional difficulties with respect to the study of analogous problems in gas phase. The mean fieldMean field theory approximation (MFA) is used for many of the most employed solvent effect theories as it permits to reduce the computational cost associated to the study of processes in solution. In this chapter we revise the performance of ASEP/MD, a quantum mechanics/molecular mechanics method developed in our laboratory that makes use of this approximation. It permits to combine state of the art calculations of the solute electron distribution with a detailed, microscopic, description of the solvent. As examples of application of the method we study solvent effects on the absorption spectra of some molecules involved in photoisomerization processes of biological systems.