[Pw_forum] relaxing a vacancy in diamond

[Giuseppe Mattioli]

> Or just shifting the atoms slightly before starting the relaxation?

Yes! If the code finds a starting symmetry, it does not break it.

HTH
Giuseppe


Quoting Nandan Tandon <nandan.tandon at gmail.com>:

> Hi,
>
> I am trying to relax a vacancy in a cubic 512 atom unit cell of diamond. It
> has
> been seen that the T_d symmetry around the vacancy is lowered to D_{2d}.
> But my system does not show this because all the atoms (first 4 neighbors)
> around the vacancy are at identical distances from the vacancy and each
> other.
>
> Initially, using a FCC supercell also gave the same relaxed structure. This
> prompted me to start with a cubic structure.
>
>
> My question is, is there a trick to do such vacancy calculations?
>
> Like starting by substituting a carbon atom with another atom to distort
> the lattice
> before creating a vacancy at the site?
>
> Or just shifting the atoms slightly before starting the relaxation?
>
> I have done few tests to ensure that the Ecut is high (80Ryd), its a Gamma
> point calculation, LDA potentials and an optimized lattice constant.
>
> Thanks and regards,
>
> Nandan.
> --
> ***********************************************************************************************
> Nandan Tandon
> Michigan State University
> East Lansing
> Michigan 48824-1226
> *************************************************************************************************



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
Via Salaria Km 29,300 - C.P. 10
I-00015 - Monterotondo Scalo (RM)
Mob (*preferred*) +39 373 7305625
Tel + 39 06 90672342 - Fax +39 06 90672316
E-mail: <giuseppe.mattioli at ism.cnr.it>