Subject: Force parameters from QM-summary

From: Marek Skowronek <[email-masked]>
Date: Mon, 9 Sep 1996 14:01:30 +0200 (METDST)

Dear CCL Users,
I would like to thank for information about the evaluation of force
parameters from QM calculations and PAPQMD program. 

Here are the answers:

1.
>From Alain Kessi

@ARTICLE{Hill94,
   author = {J{\"o}rg-R. Hill and Joachim Sauer},
   title = {Molecular Mechanics Potential for Silica and Zeolite Catalysts
      Based on ab Initio Calculations. 1. {D}ense and Microporous Silica},
   journal = {Journal of Physical Chemistry},
   volume = 98,
   year = 1994,
   pages = "1238--1244"
}

@article{Hill95,
  author = {Hill, J. R.  and Sauer, J. },
  title = {Molecular mechanics potential for silica and zeolite catalysts
    based on ab initio calculations. 2. Aluminosilicates},
  journal = {Journal of Physical Chemistry},
  year = 1995,
  month = "8~" # jun,
  volume = "99",
  number = "23",
  pages = "9536--9550",
  abstract = {A consistent force field for the simulation of protonated
    aluminosilicates is presented. It has been developed on the basis of
    ab initio calculations on molecular models following a method proposed
    in a previous paper (J. Phys. Chem. 1994, 98, 1238). The molecular models
    consist of SiO4 and protonated AlO4 tetrahedra connected to chains, rings,
    and cages. The ab initio calculations used a ''double-zeta plus
    polarization'' basis set on the Si, Al, and H atoms and a ''triple-zeta
    plus polarization'' one on the O atoms. The calculated structures of the
    finite models yield a structural model of Bornsted acidic sites which is
    consistent with observed data but more complete than models derived from
    experiments. Compared with these ab initio results the derived force field
    predicts reasonable structures for aluminosilicates, but the errors are
    larger than the errors that our all-silica potential yielded for all-silica
    polymorphs. A new method is proposed for calculating the atomic charges as
    a function of the structure, and the corresponding potential results in
    better structure predictions. The force field is applied to the calculation
    of the local structures of different bridging hydroxyl groups in faujasite,
    and it is shown that results of the same accuracy as with a shell model
    potential are obtained. The predictions for a H-faujasite (Si/Al = 2.43)
    are consistent with mean bond distances and angles deduced from neutron
    diffraction data.}
}
Hope this helps ... Best regards,
Alain Kessi ([email-masked]), at Paul Scherrer Institut, Zuerich, CH

2. From Modesto Orozco
PAPQMD is distributed by our research group. It is free for academic users

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3.