Improving description of hydrogen bonds at the semiempirical level: water-water interactions as test case
✍ Scribed by Bernal-Uruchurtu, M. I.; Martins-Costa, M. T. C.; Millot, C.; Ruiz-L�pez, M. F.
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 217 KB
- Volume
- 21
- Category
- Article
- ISSN
- 0192-8651
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✦ Synopsis
Hydrogen bonding is not well described by available semiempirical theories. This is an important restriction because hydrogen bonds represent a key feature in many chemical and biochemical processes, besides being responsible for the singular properties of water. In this study, we describe a possible solution to this problem. The basic idea is to replace the nonphysical gaussian correction functions (GCF) appearing in the core-core repulsion terms of most MNDO-based semiempirical methods by a simple function exhibiting the correct physical behavior in the whole range of intermolecular separation distances. The parameterized interaction function (PIF) is the sum of atom-pair contributions, each one having five adjustable parameters. In this work, the approach is used to study water-water interactions. The parameters are optimized to reproduce a reference ab initio intermolecular energy surface for the water-water dimer obtained at the MP2/aug-cc-pVQZ level. OO, OH, and HH parameters are reported for the PM3 method. The results of PM3-PIF calculations remarkably improve qualitatively and quantitatively those obtained at the standard PM3 level, both for water-dimer properties and for water clusters up to the hexamer. For example, the root-mean-square deviation of the PM3-PIF interaction energies, with respect to ab initio values obtained using 700 points of the water dimer surface, is only 0.47 kcal/mol. This value is much smaller than that obtained using the standard PM3 method (4.2 kcal/mol). The PM3-PIF water dimer energy minimum (-5.0 kcal/mol) is also much closer to ab initio data (-5.0 ± 0.01 kcal/mol) than PM3 (-3.50 kcal/mol). The method is therefore promising for the development of new semiempirical approaches as well as for application of combined quantum mechanics and molecular mechanics