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strange elastic constant

From: "waigen zhang" <waigen.zhang@gmail.com>
To: forum <forum@abinit.org>
Subject: strange elastic constant
Date: Tue, 3 Jul 2007 01:37:00 -0400
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Dear all,
Still the strange elastic constant problem.
I use abinit to calculate the elastic constant of alpha-Al2O3 as a check(What I need is elastic constant of N2O4).In N2O4 calculation,I tried over 20 times,but I always got negative diagonal element. What I did was,
1st,Optimize the structure.
2nd,Use the output of xred,acell,angles from the optimization step and other variables such as ecut,ngkpt,iscf...kept the same in the elastic constants calculation.There shouldn't be any mistake in the input files.If needed,I will post it.

Some of the output files of Alpha-Al2O3 are,
The first derivatives are following,is it good enough or the elements are too big?
1st derivatives              - # elements :      36
   1   1 0.25869898402403D-03 0.00000000000000D+00
   2   1 0.25869898402403D-03 0.00000000000000D+00
   3   1 0.25869898402403D-03 0.00000000000000D+00
   1   2 0.56251931526327D-03 0.00000000000000D+00
   2   2 -0.56251931526327D-03 0.00000000000000D+00
   3   2 0.00000000000000D+00 0.00000000000000D+00
   1   3 0.00000000000000D+00 0.00000000000000D+00
   2   3 0.56251931526327D-03 0.00000000000000D+00
   3   3 -0.56251931526327D-03 0.00000000000000D+00
   1   4 -0.56251931526327D-03 0.00000000000000D+00
   2   4 -0.42072581611787D-29 0.00000000000000D+00
   3   4 0.56251931526327D-03 0.00000000000000D+00
   1   5 0.25869898402403D-03 0.00000000000000D+00
   2   5 0.25869898402403D-03 0.00000000000000D+00
   3   5 0.25869898402403D-03 0.00000000000000D+00
   1   6 -0.56251931526327D-03 0.00000000000000D+00
   2   6 0.56251931526327D-03 0.00000000000000D+00
   3   6 -0.21036290805894D-29 0.00000000000000D+00
   1   7 0.00000000000000D+00 0.00000000000000D+00
   2   7 -0.56251931526327D-03 0.00000000000000D+00
   3   7 0.56251931526327D-03 0.00000000000000D+00
   1   8 0.56251931526327D-03 0.00000000000000D+00
   2   8 -0.84145163223575D-29 0.00000000000000D+00
   3   8 -0.56251931526327D-03 0.00000000000000D+00
   1   9 -0.25869898402403D-03 0.00000000000000D+00
   2   9 -0.25869898402403D-03 0.00000000000000D+00
   3   9 -0.25869898402403D-03 0.00000000000000D+00
   1 10 -0.25869898402403D-03 0.00000000000000D+00
   2 10 -0.25869898402403D-03 0.00000000000000D+00
3 10 -0.25869898402403D-03 0.00000000000000D+00
   1 13 -0.16403457711541D-02 0.00000000000000D+00
   2 13 -0.16403457711541D-02 0.00000000000000D+00
   3 13 -0.15138176513697D-02 0.00000000000000D+00
   1 14 0.00000000000000D+00 0.00000000000000D+00
   2 14 0.00000000000000D+00 0.00000000000000D+00
   3 14 0.00000000000000D+00 0.00000000000000D+00

The calculated elastic constants are following,which are far away from the well-known results.Also there seems to be some mistake about this matrix analysied from symmetry.C14 shouldn't be zero and........

Elastic Tensor (relaxed ion) (unit:10^2GP):
(at fixed electric field boundary condition)

   9.0146811   3.0170874   1.2282716 -0.0000014 -2.5594517   0.0000081
   3.0170874   9.0146790   1.2282701 -0.0000021    2.5594490 -0.0000043
   1.2282716   1.2282698   7.7354829 -0.0000015   0.0000067 -0.0000015
   0.0000003 -0.0000005 -0.0000003   1.5197380   0.0000032   2.5594511
-2.5594517   2.5594490   0.0000002   0.0000087    1.5197329   0.0000042
   0.0000083 -0.0000049 -0.0000003   2.5594511   0.0000003   2.9988020

Regards,
WG

strange elastic constant, waigen zhang, 07/03/2007
- Re: [abinit-forum] strange elastic constant, D. R. Hamann, 07/09/2007