No, I don't think there is currently anyway to do this kind of biasing with rotational DOFs
in LAMMPS. Someone would have to add code for it.
Steve
On Tue, Oct 3, 2017 at 2:25 PM, Qi Liu <iamllqq@...24...> wrote:
Dear Lammps users,
I'm currently working on the simulations of dipoles in a shear flow. The shear flow has the velocity in the x direction and vorticity Ω = -0.5 dv_{x}/dy in the z direction. The vorticity makes the particles spin with the flow, so the rotational friction is proportional to the relative angular velocity of particles. Then the 2 friction terms in the Langevin equations are -ζ_{t} [v_{j}-v(r_{j})] in the translational momentum equation and -ζ_{rot} [ω_{j}-Ω(r_{j})] in the angular momentum equation. j is the particle index.
I know I can thermostat the system with a translational velocity bias like in the following:
#for comparison with temperature computations with a bias
compute comp_tTrRot all temp/sphere dof all
compute comp_tTr all temp
compute comp_tRot all temp/sphere dof rotate
fix fix_def all deform 1 xy erate ${xyrate} remap v flip yes units box compute comp_tTrDef all temp/deform compute comp_tTrRotDef all temp/sphere bias comp_tTrDef dof all
#for comparison with compute temp/deform compute comp_tTrProf all temp/profile 1 0 0 y 20
fix fix_ext all efield 0 ${Hy} 0 fix fix_nve all nve/sphere update dipole fix fix_lang all langevin ${temp} ${temp} ${damp} ${randomNum3} omega yes fix_modify fix_lang temp comp_tTrRotDef
My question is, is there a way to add an angular velocity bias to the Langevin thermostat besides the translational velocity bias from "compute temp/deform"? "compute temp/rotate" subtracts center of mass velocity and angular velocity, so it doesn't satisfy the requirement. Did I miss something important?