[Pw_forum] Calculating stable lattice parameter for non-cubic structure

[efi dwi indari]

Dear All,

Please let me repost my old question since it was considered as 'spam' in
my mailbox:

I am now on my way in determining stable lattice parameter of both
orthorhombic and tetragonal structures. Previously everything was going
well when I calculated the cubic one as I obtained the U-curve from which I
got the value of stable lattice parameter which corresponds to the lowest
total energy.

Yet, when I move forward to the orthorhombic and tetragonal ones and when I
varied one of the lattice parameters (while the other(s) remain(s)
constant), I could not obtain the U-curve. Instead, I got a linear curve,
with lower total energy as I go to smaller lattice parameter. Does anyone
have any idea how to deal with this issue? I have already googled but
unfortunately not yet found any solution.

My idea for tetragonal structure is to approximate it as pseudocubic one;
yet I still do not have any idea what to do with the orthorombic one.

Any help would be really appreciated. Thank you in advance.

Best Regards,

Efi Dwi Indari
Research assistant, Bandung Institute of Technology
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