A new method for deriving atomic charges and dipoles for n, -alkanes: investigation of transferability and geometry dependence

Atomic charge models are known to be unsatisfactory for representing the ab initio electrostatic potential (ESP) of n, -alkanes. A new method for deriving atomic charges and dipoles is proposed and applied to n-alkanes ranging from C4 to C10. Electrostatic parameters found by this method reproduce accurately the ab initio ESP. The issues of transferability and conformational dependence are also addressed by introducing charges and dipoles taken from a truncated distributed multipole analysis, in the same spirit as the restrained electrostatic potential method. A transferable model is proposed for larger alkanes (>C10). We also estimate the error made when using a set of Boltzmann-weighted electrostatic parameters for all conformers. The reduced number of electrostatic sites considered in our model makes it suitable for computer simulation of liquid n-alkanes.