[gmx-users] How to control the temperature when using an electric field?

[David van der Spoel]

On 2011-04-23 09.38, Apoorv Kalyankar wrote:
> In GROMACS, I believe that whenever an external force is applied, the
> mean velocity of the group is subtracted before rescaling the
> velocities and then the mean velocity is added back in. So if you are
> expecting  a plug like flow then there should not be any problem. In
> other cases also, it should not create a problem since your external
> electric field is not that large.
>
This is correct for the acceleration option, but not for the electric 
field. Hence the E-field will introduce friction that will heat up the 
system.

> And yes you should not remove the center of mass motion of the
> molecules otherwise you will get zero velocity.
Correct.
>
> Apoorv
>
> On Fri, Apr 22, 2011 at 2:09 AM, lammps lammps<lammp2forum at gmail.com>  wrote:
>> Hi,
>>
>> I want to use the option of E_x = 1   0.01  0 to add an electric field to
>> the simulated system in NVT ensemble.
>>
>> Because there should exist an no zero velocity of center-of-mass in the x
>> direction. It seems that it is wrong to directly use the nose-hoover to
>> control the temperature.
>>
>> it is also not reasonable to use nstcomm   = 1, because the velocity of
>> center-of mass in the x-axis should be kept when runing.
>>
>> So, How to control the temperature? When calcating the temperature in the
>> process of simulations, how to exclude the velocity of center-of-mass of x
>> direction for controling the right T?
>>
>> Thanks in advance.
>>
>> --
>> wade
>>
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-- 
David van der Spoel, Ph.D., Professor of Biology
Dept. of Cell & Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:	+46184714205.
spoel at xray.bmc.uu.se    http://folding.bmc.uu.se