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FREE-ENERGY CALCULATION OF A PROTEIN AS A FUNCTION OF TEMPERATURE AND PRESSURE : MULTIBARIC-MULTITHERMAL MOLECULAR DYNAMICS SIMULATIONS

Free-energy calculation is one of the main topics in thermodynamics. However, biomolecules such as proteins have complicated free energy surfaces with many local minima. Conventional molecular dynamics (MD) and Monte Carlo (MC) simulations in physical ensembles, such as the canonical and isobaric-isothermal ensemble, tend to get trapped in these local-minimum states and cannot give the correct free-energy difference between different-conformational states. In order to avoid this difficulty, generalized-ensemble algorithms such as the multicanonical algorithm are frequently employed. However, because the multicanonical simulation is performed in a fixed volume, neither the pressure dependence nor temperature dependence at certain pressure can be investigated as in experiments. To overcome this difficulty, the author recently proposed multibaric-multithermal MD and MC algorithms. In this ensemble, two-dimensional random walks in the potential-energy space and in the volume space are realized. In this paper, the multibaric-multithermal molecular dynamics algorithm is reviewed and application to a 10-residue protein, chignolin is presented.