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Calculating free energies for diffusion in tight-fitting zeolite-guest systems: Local normal-mode Monte Carlo
 

Summary: Calculating free energies for diffusion in tight-fitting zeolite-guest systems:
Local normal-mode Monte Carlo
Srinivas C. Turaga
Department of Chemistry and Department of Computer Science, University of Massachusetts,
Amherst, Massachusetts 01003
Scott M. Auerbacha)
Department of Chemistry and Department of Chemical Engineering, University of Massachusetts,
Amherst, Massachusetts 01003
Received 27 November 2002; accepted 13 January 2003
We present an efficient Monte Carlo algorithm for simulating diffusion in tight-fitting host­guest
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

  

Source: Auerbach, Scott M. - Department of Chemistry, University of Massachusetts at Amherst

 

Collections: Chemistry