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The '''Flying ice cube''' <ref>[http://www3.interscience.wiley.com/journal/33911/abstract Stephen C. Harvey, Robert K.-Z. Tan, Thomas E. Cheatham III "The flying ice cube: Velocity rescaling in molecular dynamics leads to violation of energy equipartition", Journal of Computational Chemistry '''19''' pp. 726-740 (1998)]</ref> | The '''Flying ice cube''' <ref>[http://www3.interscience.wiley.com/journal/33911/abstract Stephen C. Harvey, Robert K.-Z. Tan, Thomas E. Cheatham III "The flying ice cube: Velocity rescaling in molecular dynamics leads to violation of energy equipartition", Journal of Computational Chemistry '''19''' pp. 726-740 (1998)]</ref> | ||
is an artificial situation encountered in [[ molecular dynamics]] simulations | is an artificial situation encountered in [[ molecular dynamics]] simulations. It is due to an incorrect [[equipartition]] of energy | ||
by [[Thermostats| | by the [[Thermostats| thermostat]], in particular, by thermostats that implement some form of periodic velocity rescaling, such as the [[Bussi-Donadio-Parrinello thermostat]]. The net result is that an instability forms where the kinetic energy may be drained from some [[Degree of freedom| degrees of freedom]] and be incorrectly fed into others. A manifestation of this would be the kinetic energy from the high frequency bond vibrations and angle bending in a system composed of, say, flexible [[Water models|water molecules]] ending up in the zero frequency mode of the kinetic energy of the system as a whole (''i.e.'' centre of mass translation); the molecular motions would become frozen, resulting in a ''flying ice cube''. Note that despite the name, this situation is not limited to simulations of water. | ||
==Solutions== | |||
The net result is that an instability forms where the kinetic energy may be drained from some [[Degree of freedom| degrees of freedom]] and be incorrectly fed into others. A manifestation of this would be the kinetic energy from the high frequency bond vibrations and angle bending in a system composed of, say, flexible [[Water models|water molecules]] ending up in the zero frequency mode of the kinetic energy of the system as a whole (''i.e.'' centre of mass translation); the molecular motions would become frozen, resulting in a ''flying ice cube''. Note that despite the name, this situation is not limited to simulations of water. | *Use a thermostat that reassigns the velocity distribution, rather than rescaling the actual velocities. (see: [[Andersen thermostat]]) | ||
*Reduce the frequency of the velocity rescaling. | |||
*Increase the temperature bath coupling parameter. (see: [[Berendsen thermostat]]) | |||
==References== | ==References== | ||
<references/> | <references/> | ||
; | ;Related reading | ||
*[http://dx.doi.org/10.1007/s40436-013-0024-3 Liu-Ming Yan, Chao Sun, Hui-Ting Liu "Opposite phenomenon to the flying ice cube in molecular dynamics simulations of flexible TIP3P water", Advances in Manufacturing '''1''' pp. 160-165 (2013)] | |||
[[category: molecular dynamics]] | [[category: molecular dynamics]] | ||