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

Ridwan Agbaoye agbaoyeridwan at yahoo.com
Thu Jan 21 09:45:00 CET 2016

1.Ensure you compute your input file correctly, check your ibrav to confirm if it correlate with that of  orthorombic and tetragonal, check the required celldm(1)..celldm(6) and make sure you used the correct cell dimension assigned to your lattice structure through INPUT_PW.html
2. You should have an idea of the experimental lattice or optimized lattice parameter from other research work you can find around, then set your celldm(1)  to + or - the optimized lattice parameter you got while other lattice parameters become constante.g if the optimized celldm(1) from other research or experimental value is 10 bohr you can vary your celldm(1) from 8 bohr to 12 bohr with an increment of 0.02, which depends on how much computation resource or how expensive your computation is.
if you get a linear graph with positive gradient you next celldm trial should be less than your minimum celldm from your graph but if your linear graph is such that its gradient is negative you next trial for celldm should be higher than your minimum celldm from your graph... 
Good luck.

Agbaoye Ridwan OlamideFederal University of Agriculture, AbeokutaM.Sc. in view 

    On Thursday, January 21, 2016 12:49 AM, efi dwi indari <efidwiindari at gmail.com> wrote:

 Dear All,

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) remains 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. 

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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