Relation of velocity generation wrt tc-grps

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1

GROMACS version: 2021.5
GROMACS modification: No
Hello everyone,
I want to simulate a system where there are two species which are coupled with two different temperature baths as follows:
tc-grps = GRP1 GRP2
tau_t = 2 2
ref_t = 500 15000
gen-vel = yes
gen-temp = 500
gen-seed = -1

Is there any additional parameter or a way in Gromacs so that I could generate velocities at two different temperatures according to Maxwell distribution with respect to the tc-grps at the same time as my group 1 is not stable above 600 K whereas I would need to achieve higher kinetic energy for more effective collisions. (Group 2 is stable upto 20000 K)

Hence I want to generate velocities at a temperature of 15000K for group 2 and 500K for group 1.

I would be highly obliged if anyone can share their ideas or views on this problem.

2

You cannot supply multiple values to gen-temp because having two different temperatures is unphysical (as is having separate groups at different temperatures).

3

Thank you so much for your reply.
Yes, I am dealing with a non-equilibrium system where just one group has an effective temperature and I want to feed higher temperature to the other group.
Even if the system remains unphysical, is there any way I can achieve this by providing two different temperatures as input.
If yes, which parameters shalll I modify?

Thank you very much for your help

4

Unphysicality aside, regardless of the starting temperature, the thermostat will ensure they reach their reference temperature after a few tau_t duration (unit is ps)

5

Alternatively, one can soften the initial difference in temperature by using the simulated annealing code, so temperatures are all generated at one set value, but then one group can be heated to a different value.

6

Thanks a lot for your reply,
I also wanted to know, If I follow your suggestion and perform simulated annealing followed by heating, would it be possible to selectively generate velocity for the group at the higher temperature without affecting the other group.

Thank you so much.

7

No, gen-temp takes one argument that is applied universally. So you would generate the velocities of everything at 500 K, then use the annealing code to heat one group up from there. Once at the target temperature, you could continue running at the non-equal temperatures.

8

Thank you very much for your answer, I would certainly try to achieve this.