By Arun Yethiraj
University of Wisconsin

Macromolecular systems have interesting behavior on a range of length-scales and timescales. Computational study of these systems therefore requires modeling at multiple levels of detail. The development of coarse-grained (CG) models for macromolecules is an exciting and challenging frontier of research in computational chemistry. The ultimate goal is to develop a model that is computationally feasibly but captures the essential physical chemistry. I will discuss our recent efforts in this area. We have developed a CG model of water called the big multipole water (BMW) model which is in the spirit of the MARTINI model (four water molecules are grouped into one site) but includes electrostatic interactions including a quadrupole moment. I will discuss the performance of this force field for several problems including the hydrophobic effect, the behavior of peptides at membranes, the self-assembly and phase behavior of lipid/peptide mixtures, and the conformational properties of polymers. The results demonstrate the importance of electrostatic correlations in the water model, and suggest that these models can be useful in investigating complex fluids over long length-scales.