Assessment of Two Surface Monte Carlo (TSMC) method to find stationary points of (H2O)15 and (H2O)20 clusters |
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Authors: | Pradipta Bandyopadhyay |
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Institution: | (1) Department of Biotechnology, Indian Institute of Technology, Guwahati, 781039, Assam, India |
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Abstract: | The Two Surface Monte Carlo (TSMC) technique reduces computational cost by using a computationally cheap biasing potential,
which guides the molecular system to explore the potential energy surface of interest. It was shown earlier that the Effective
Fragment Potential (EFP) can be a good choice for this biasing potential (Bandyopadhyay, J Chem Phys 122:091102, 2005) when
the potential energy surface of interest is quantum mechanical. This may help in expanding the applicability of TSMC, since
finding a good biasing potential is a major challenge. In the present work, the viability of TSMC method in finding stationary
points of large molecular system is investigated using EFP as the biasing potential and RHF theory as the potential of interest.
TSMC is applied to find the stationary points of water clusters of size 15 and 20. A semi-automated method starting from random
geometries, without using any chemical intuition, found several stationary points. The simulated annealing method was used
to refine the structures obtained from TSMC. Among the several low-energy structures obtained for 15 water cluster, one minimum,
about 1 kcal/mol higher than the global minimum, was found. However, for 20 water cluster, no structure very close to the
global minimum was obtained. Several strategies, learned from the experience of the present work, are discussed for improving
the TSMC method, including the acceptance between the two energy surfaces.
Contribution to the Mark S. Gordon 65th Birthday Festschrift Issue. |
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Keywords: | Monte Carlo Effective fragment potential Stationary points Water clusters Global minimum |
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