On validity of current force fields for simulations on boron nitride nanotubes

Past molecular dynamics studies of boron-nitride nanotubes have used van der Waals parameters from generic force fields, combined with various values for the partial charges on the boron and nitrogen atoms. This paper explores the validity of these parameters by first using quantum chemical packages CPMD and Gaussian to compute partial charges for isolated and periodic boron nitride nanotubes, both with and without water. Then, in order to test the accuracy of the molecular mechanics force field using our computed charges, we calculate the interaction energy between each water molecule in a hydrated nanotube with the nanotube itself using two methods: firstly using a quantum chemical calculation, and secondly using the molecular mechanics force field. We show that, in order to obtain satisfactory agreement in the interaction energies the boron and nitrogen LennardJones parameters must be adjusted from their usual values. Modified Lennard-Jones parameters and partial charges, obtained by fitting, are presented as candidates for future molecular dynamics simulations of hydrated boron nitride nanotubes.