Accurate Description of Intermolecular Interactions

Despite the considerable progress in the efficiency and quality of ab initio electronic structure theory the description of intermolecular interactions in extended systems is still (and probably will remain) a time consuming process. Thus, methodologies to reduce the dimensionality of the problem while retaining accuracy in the relevant degrees of freedom are of importance. Such approaches have been successfully applied to molecular clusters. Their generalization and application to biologically relevant systems are one core area of our research. Other issues concern the interaction of a molecular system with its environment by electrostatic and van der Waals forces. For example, important contributions in the interaction of CO molecules with the surrounding protein matrix arise from electrostatic (dipole, quadrupole terms) terms in myoglobin. Recently, a new model has been developed that uses fluctuating point charges as a function of the bond length in CO. It has bee successfully applied to calculating the infrared spectrum of photodissociated CO in myoglobin. For the first time, the infrared spectrum was quantitatively correctly described.