Thank you for your message.
I think if we relax the other two lattice parameters at the same time, the
obtained values should be Young's modulus, but not C_33.
I have checked my calculations, the k points and cutoff energies have been
carefully tested. I wonder if the error comes from the basis sets we used
(DZP)? Is there anyone who used to perform similar calculations? Is that a
common error in SIESTA? I urgently need your help, thank you!
Best regards,
Chun
----- Original Message -----
From: Vasilii Artyukhov
To: SIESTA-L@listserv.uam.es
Sent: Monday, March 19, 2007 4:41 PM
Subject: Re: [SIESTA-L] Posible SPAM: elastic constant calculations
I believe that if you're willing to apply strain in the c direction only, you
might also want to relax the other two lattice parameters. Obviously this will
decrease your values, maybe to something reasonable.
2007/3/19, Chun Li <[EMAIL PROTECTED]>:
Dear SIESTA users,
I used SIESTA to calculate the elastic constant C_33 of bulk ZnO. Both LDA
and GGA are employed, respectively. But the obtained results are much larger
than the experimental value (for LDA, I got 358 GPa; GGA, 282 GPa; but the
experimental value is around 210 GPa). I wonder why such big error appears?
What important factors might be responsible for that? Could anyone give me some
ideas?
In my calculations, first the cell is fully relaxed; after that I apply
different strains in the c direction and evaluate their total energies,
respectively. Then I fit the obtained energies to obtain the elastic constant.
In both relaxation and energy calculations, double-zeta polarized numerical
atomic orbitals basis sets for both Zn and O are used.
Thank you and best regards,
Chun Li
