Srinivas C. Turaga and Scott M. Auerbach, ``Calculating Free
Energies for Diffusion in Tight-Fitting Zeolite-Guest Systems:
Local Normal-Mode Monte Carlo,''
J. Chem. Phys. 118, 6512-6517 (2003).
Abstract
We present an efficient Monte Carlo algorithm for simulating diffusion
in tight-fitting host-guest systems, based on using zeolite normal modes.
Computational efficiency is gained by sampling framework distortions
using normal-mode coordinates, and by exploiting the fact that zeolite
distortion energies are well approximated by harmonic estimates.
Additional savings are obtained by performing local normal-mode analysis,
i.e., only including the motions of zeolite atoms close to the jumping
molecule, hence focusing the calculation on zeolite distortions relevant
to guest diffusion.
We performed normal-mode analysis on various silicalite structures to
demonstrate the accuracy of the harmonic approximation.
We computed free energy surfaces
for benzene in silicalite, finding excellent agreement with previous
theoretical studies. Our method is found to be orders-of-magnitude
faster than comparable Monte Carlo calculations that use conventional
forcefields to quantify zeolite distortion energies. For tight-fitting
guests, the efficiency of our new method allows flexible-lattice simulations
to converge in less CPU time than that required for fixed-lattice simulations,
because of the increased likelihood of jumping through a flexible lattice.
Prof SM Auerbach
4 April 2003