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From: |
Qi Liu <iamllqq@...24...> |

Date: |
Tue, 3 Oct 2017 16:25:10 -0400 |

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

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

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

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?

Thank you!

Regards,

Qi

**Follow-Ups**:**Re: [lammps-users] Thermostating dipoles with angular velocity bias in shear flow***From:*Steve Plimpton <sjplimp@...24...>

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