Hello,
I have questions in usage of thermostat. I am trying to simulate a
gravity driven flow with 0.2 reduced acceleration units. Upper and
lower walls are at rest (using setforce) and thermostat is applied to
the fluid. Streaming direction is x while the channel width is along
z, and is 20 molecular diameter. I am calculating the temperature
using temp/profile and temp/partial methods.
In temp/partial the arguments for [x y z] are [0 1 1] (Case 1)
respectively, no thermostat acts in the streaming direction. To test
the accuracy of this computation with profile unbiased thermostat
(PUT), two separate tests using temp/profile are performed, where
arguments for [x y z] are [0 1 1] (Case 2) and [1 1 1] (Case 3,
temp/partial acts in streaming direction too). Number of bins (not
averaging bins) are kept 20 for temp/partial case in z dimension.
The resulting velocity profile for Case 1 matches exactly with Case 3,
while Case 2 results in less streaming velocity. My questions are:
1. I would expect Case 1 and Case 2 to produce similar results, if my
interpretation is wrong, please correct me here.
2. Does the value of acceleration complies with linear response
regime. Decreasing the value of acceleration by tenfold (0.02) leads
me to matching velocity profiles within simulation errors, while the
original case (0.2), streaming velocities differ significantly.
3. Which of the above three ways of computing temperature is recommended?
Here is a little excerpt from the script for Case 2. OW is the working
fluid, WW is wall. Units are LJ.
compute mobile OW temp/profile 0 1 1 z 20
fix 1 WW setforce 0.0 0.0 0.0
fix 2 OW nvt temp 3.7622 3.7622 0.128433
fix 3 OW gravity 0.2 vector 1 0 0
fix_modify 2 temp mobile
Ravi Bhadauria