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 nb initio electrostatic potential (ESP) of rt-alkanes. A new method for deriv ing atomic charges and dipoles is proposed and applied to n-alkanes ranging from C-4 to Clo Electrostatic parameters found by this method reproduce ac curately the nb initio ESP. The issues of transferability and conformationa l dependence are also addressed by introducing charges and dipoles taken fr om a truncated distributed multipole analysis, in the same spirit as the re strained electrostatic potential method. A transferable model is proposed f or larger alkanes (>C-10) We also estimate the error made when using a set of Boltzmann-weighted electrostatic parameters for all conformers. The redu ced number of electrostatic sites considered in our model makes it suitable for computer simulation of liquid n-alkanes.