Re: [ESPResSo-users] Changes in the Langevin thermostat

[Georg Rempfer]

I rather think that

    gamma_new = gamma_old * m

That is because the input parameter gamma_old denoted the inverse relaxation time (1/T), where 1/T=gamma/m with gamma the actual friction coefficient as in the Langevin equation

    d^2 x / dt^2 = -gamma/m * dx/dt + R

Espresso now internally divides by m, so that gamma_new=gamma.

On Wed, Nov 18, 2015 at 4:15 PM, Paul Peterson <address@hidden> wrote:

Thanks Georg, guess that's the way. 

Then, the new gamma coefficient for a particle of mass m should be (m / gamma_OLD), right?

Paul

2015-11-18 16:17 GMT+01:00 Georg Rempfer <address@hidden>:

Hello Paul,

you might want to check out the LANGEVIN_PER_PARTICLE feature in the User's Guide.

Greetings,

Georg

On Wed, Nov 18, 2015 at 2:59 PM, Paul Peterson <address@hidden> wrote:

Hello everybody,

the 30 october version of the User Manual warns that the meaning of the gamma parameter for the Langevin thermostat has been changed from a relaxation time, as it used to be, to a friction coefficient. 

Can anybody tell me what is the conversion formula from old to new parameters?

Reading the paragraph, I guess the mass's particle is involved; but what if I have two types of particles with different masses?

Thanks, best

Paul