Friday, August 10, 2012

1208.1928 (Sriram Ganeshan et al.)

Quantum zero point effects using modified Nose-Hoover thermostats    [PDF]

Sriram Ganeshan, Rafael Ramírez, M. V. Fernández-Serra
Molecules like water have vibrational modes with zero point energy well above room temperature. As a consequence, classical molecular dynamics simulations of their liquids largely underestimate the kinetic energy of the ions, which translates into an underestimation of covalent interatomic distances. Zero point effects can be recovered using path integral molecular dynamics simulations, but these are computationally expensive, making their combination with ab initio molecular dynamics simulations a challenge. As an alternative to path integral methods, from a computationally simple perspective, one would envision the design of a thermostat capable of equilibrating and maintaining the different vibrational modes at their corresponding zero point temperatures. Recently, Ceriotti et al. [Phys. Rev. Lett. 102, 020601 (2009)] introduced a framework to use a custom-tailored Langevin equation with correlated-noise that can be used to include quantum fluctuations in classical molecular-dynamics simulations. Here we show that it is possible to use the generalized Langevin equation with suppressed noise in combination with Nose-Hoover thermostats to achieve an efficient zero-point temperature of independent modes. We apply this new thermostat to the molecular dynamics of a flexible water force field. We address the question of whether thermostating each mode to its zero point temperature is enough to simulate nuclear quantum effects in water.
View original: http://arxiv.org/abs/1208.1928

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