About thermostat 'tcoupl' im metadynamics

[pratiti bhadra]

Dear All,

Can I used any thermostat (as per force field, which is best for the force field ) in "meta dynamics" simulation for maintaining temperature of system through simulation.
Or I have to used Langevin thermostat for "meta dynamics" simulation.

Regards,
Pratiti

[Giovanni Bussi]

Hi,

the main difference is between local thermostats (such as Langevin, massive Nosé-Hoover, etc) and global thermostats (such as standard Nosé-Hoover, stochastic velocity rescaling, etc).

Global thermostats usually do not affect the kinetic properties, which would be important e.g. if you want to do Markov state models of transition path sampling. However, if you do metadynamics you are not usually interested in kinetics (an exception might be if you try to reconstruct dynamics with Tiwary & Parrinello method). So from this point of view there is no significant advantage in global thermostats.

An advantage of global thermostats is that they tend to sample phase space faster. This could be a good point. I actually always use a global thermostat when doing metadynamics on solvate molecules.

The only important drawback of global thermostats is that they do not control the temperature separately for subsets of your system. That's why many people use separate global thermostats for water and solute, to be sure that they do not equilibrate at different temperature (mostly because for the same time step energy drift might be different in water and solute).

Specifically about metadynamics, in case you use a very high deposition rate (as you often do with ab initio MD, where in a few tens of ps you want to surmount a barrier of several kcal/mol) you might find global thermostats problematic since there could be a significant amount of energy accumulated on the biased atoms. I don't have direct experience, but I heard sometime ago someone observing large temperature gradients in a ab-initio metadynamics simulations. If you think this could be a problem for your system, you might better use Langevin (or another local thermostat).

Giovanni

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