Efficient ab initio sampling methods in rate constant calculations for proton-transfer reactions

In this article, the classical potential based importance Monte Carlo sampl ing method of Iftimie [J. Chem. Phys. 113, 4852, (2000)] is applied to an a b initio simulation of the proton transfer tautomerization reaction of malo naldehyde in an aprotic, nonpolar solvent. It is demonstrated that ad hoc b ond-energy bond-order relations derived from bond evolution theory combined with Pauling's valence bond ideas can be used to construct a molecular mec hanics guidance potential for the simulation of the proton transfer reactio n which improves the statistics of the calculation by three orders of magni tude. The sampling method is extended to simulations in which quantum effec ts are treated using the imaginary time path-integral representation. A new algorithm based on multiple Markov chain theory is introduced by which it is possible to obtain very short integrated correlation lengths in calculat ions of quantum static correlation functions. (C) 2001 American Institute o f Physics.