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[lammps-users] damp fix press/berendsen and fix langevin
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[lammps-users] damp fix press/berendsen and fix langevin


From: ruiyan <r-yan14@...61...>
Date: Fri, 7 Jul 2017 19:06:31 +0800 (GMT+08:00)

Dear all, 

I have several questions related to fix press/berendsen command and fix langevin command.

1. In fix press/berendsen command, we need to specify Pdamp and modulus value. From lammps manual of 2016Nov17, the recommneded value for Pdamp is 1000 timesteps, but I don't know what modulus mean in this command? Do we need to specify modulus value according to the real modulus of the material we simulate? Or we just need to consider the product of Pdamp and modulus to make pressure relax in a reasonable rate?  If the latter one is  correct, is there a recommend value for modulus? 

2. In fix langevin command,  

(1) how to specify Tdamp? I don't find a recommended value for it. 

(2) Especially how to specify scale values? I know that the mass and size of different atom types should be accounted for in the choice of ratio values, but how? Suppose I define two atom types in my simulation box. Condtion1, for type1, mass=1, size=1, and type2, mass=1, size=2, what are sacle values for type1 and type2?  

(3) Condition2, for type1, mass=1, size=1, and type2, mass=2, size=1, what are sacle values for type1 and type2?  

(4) Condition3, for type1, mass=1, size=2, and type2, mass=4, size=1, what are sacle values for type1 and type2?  


Thanks and look forward to your reply. 

Rui