[Pw_forum] calculation of lattice parameters[ i.e. 'a' and 'c/a' ratio] for HCP metals say Mg.

[bisu123 at platinum.materials.iisc.ernet.in]

Dear all,
             Can someone tell me the correct methodology to start with
lattice  parameters estimation for HCP metals. I shall tell
what I did for my earlier simulations involving Magnesium.

First, I fixed the ecut value and then used the same ecut value to fix the
ecutrho value. Then using the fixed ecut and ecutrho, I varied the
k-points to obtain the K-points. in my case I obtained [12 12  9]. Then
for lattice  parameter calculation, [ having fixed ecut, ecutrho, k-points
of course]  I fixed  'c/a' ratio initially[ c/a= sqrt(8/3)] and varied the
'a' across the ideal value of 'a'[ a=3.21 Angstroms =6.06602 at. units]
and obtained the value for 'a' corresponding for the minimum energy
configuration. Then using the obtained 'a' in the previous step, I varied
the 'c/a' ratio across the ideal value to obtain c/a=1.58, corresponding
to the minimum energy configuration. However this estimate involves
significant error since the ideal value for c/a( for Mg=sqrt(8/3)=1.624).
Then I used the value for 'c/a' in the previous step[ i.e 1.58] and varied
'a' to find the value of 'a'.

Finally, I obtained a=6.1 a.u=3.23 angstroms, c/a=1.58. The
psuedopotential I used for Mg is  Mg.pw91-np-van.UPF .

Thanks all,

regards,
Biswaranjan Dash
Research Scholar,
Deformation Mechanisms Modeling Group,
C/0- Asst Prof S.Karthikeyan
Indian Institute of Science,Bangalore
India





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