[CP2K-user] [CP2K:12255] Negative Pressure in NVT ensemble

Thomas Kühne tku... at gmail.com
Mon Sep 23 17:59:38 UTC 2019

Dear Ramanish Singh, 

minimal mispredictions within lattice constant and vectors 
may entail large changes in the pressure. So observing a 
rather large negative pressure is not necessarily indicative 
of a problem. Beside that the usage of good basis sets and 
tight SCF convergence is essential, it is hard to say anything 
specific without detailed knowledge on what you plan to do. 

Thomas Kühne

> Am 23.09.2019 um 18:01 schrieb Ramanish Singh <sing... at umn.edu>:
> Hi,
> I am simulating a system of Iodine atoms using BLYP functional in the NVT ensemble.
> But when I am calculating the pressure, using   STRESS_TENSOR ANALYTICAL in the FORCE_EVAL section, my pressure (average of the xx,yy and zz elements) is coming out to be negative which is far from the experimental pressure at that density and Temperature. 
> I can not figure out why this is happening. 
> Thanks,
> Ramanish Singh
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Thomas D. Kühne
Dynamics of Condensed Matter
Chair of Theoretical Chemistry
University of Paderborn
Warburger Str. 100
D-33098 Paderborn
tdku... at mail.upb.de

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