Over the past decades molecular simulation has become an increasingly important tool in predicting and interpreting chemical processes. Inherent in these simulations is the assumption that the nuclei behave classically. However, for processes involving light particles such as hydrogen the quantum mechanical nature of the particles can dramatically alter their structure and dynamics. I will present our recent advances in developing approaches to treat nuclear quantum mechanical fluctuations in condensed phase systems and to calculate isotope effects at a cost barely more than the a corresponding classical simulation. These advances allow us to investigate, in unprecedented detail, chemical systems where the inclusion of quantum mechanical effects is essential to obtain the correct result. I will illustrate the utility of these approaches with recent applications ranging from fractionation of hydrogen isotopes between liquid water and its vapor, which are a major input in climate modeling, to the biologically important proton delocalization in enzyme active sites.  Figure: Proton delocalization in the Ketosteroid Isomeraze (KSI) active site from our recent ab initio path integral simulations. These simulations incorporate the quantum nature of both the electrons and nuclei. The left panel shows the full QM/MM simulation of solvated KSI. The blue smeared particles on the right panel show the uncertainty of the protons positions obtained from our simulations. This quantum mechanical delocalization of the protons acts to stabilize the substrate in the extended hydrogen bond network in the catalytic intermediate.

Quantum fluctuations in hydrogen bond networks: From atmospheric science to enzyme catalysis

248th National Meeting (2014)

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