[Pw_forum] relaxing a vacancy in diamond

[Nandan Tandon]

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.
-- 
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Nandan Tandon
Michigan State University
East Lansing
Michigan 48824-1226
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