[Pw_forum] Cannot reach the target temperature in vc-md calculation using pwscf; and where I can find the updated velocities?

[Alexey Akimov]

Dear Tian,

If i remember it correctly there was an issue (bug) with QE v.4.* regarding temperature control with vc-md. I once found it somewhere in the QE archive. The problem was supposed to be fixed in v.5. Also the temperature should be correct if you do just md (not vc-md) simulation,even in version 4. 
P.S. Please, correct me if i'm wrong with something. 

Best,
Alexey

----- Original Message -----
From: "Tian Lan" <tianlan at caltech.edu>
To: "PWSCF Forum" <pw_forum at pwscf.org>
Sent: Friday, November 30, 2012 12:49:59 AM
Subject: [Pw_forum] Cannot reach the target temperature in vc-md calculation using pwscf; and where I can find the updated velocities?



Dear all, 

I am running vc-md of a cuprite structure with 2 by 2 by 2 supercell. When I set the tempw=300, it does converge but the equilibrium temperature seems to be only 190K. It starts from 280 and all the way down to 190K and converges there. Actually I did not find many controls on it, below is what my current setups for &ions and &cells. 

I kept trying different setups, but has little effect, for example, I tried different 'dt' from 20 to 50, different 'ion_temperature' choices, 'tolp' or 'nraise'. I also used a primitive cell, the actual temperature can be only 108K or so. Therefore, I am not sure whether it has something to do with the cell size, or the temperature calibration issue, or some setup would substantially influence the temperature control. 

&ions 
tempw=300, 
ion_temperature= 'rescaling', 
tolp=20, 
nraise=1, 
pot_extrapolation='second-order', 
wfc_extrapolation='second-order', 
/ 
&cell 
cell_dynamics = 'pr' , 
press = 0.00 
/ 

Besides of it, I have a stupid question because I did not find any information about the atom velocities. I only find updated coordinates and forces in .out file. In .save folders, I did not find anything either. My control icons for print are as follows: 

disk_io='high' 
! wf_collect=.TRUE. 
pseudo_dir = '.', 
outdir='\temp' 
tstress =.true., 
tprnfor =.true., 

Thank you in advance if you have any idea about these. 
Best Regards, 
Tian 
-- 
Lan, Tian 
Ph.D. Candidate, Department of Applied Physics and Materials Science 
California Institute of Technology, 
Caltech M/C 138-78, Pasadena, CA, 91125 

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-- 
Dr. Alexey V. Akimov

Postdoctoral Research Associate
Department of Chemistry
University of Rochester

aakimov at z.rochester.edu