lattice constant optimize

Message

huijiany · #1 Post by **huijiany** » Fri Feb 27, 2009 12:46 am

when optimize the lattice constant, I just want to make C axis
change, and keep a and b axis unchanged. How can I do?

forsdan · #2 Post by **forsdan** » Fri Feb 27, 2009 7:38 am

There is no automatic way to do this in VASP, since there is no support in the current version for this kind of constraint relaxation.

The recommended thing that you can do is however to write a small script that generate your input files with different c-axis where you keep the a,b axis unchanged, and then run VASP for each input-set under constant volume and constant shape.

Best regards,
/Dan

mrm · #3 Post by **mrm** » Sat Feb 28, 2009 2:58 am

Hello,

I think it is possible to use "Selective Dynamics" in the POSCAR file and choose explicitly (by saying T or F for each x, y, z coordinate of each atom) if a degree of freedom can change. I believe that you can constrain the degrees of freedom to the c-axis in this way. Please check VASP manual to make sure about this. I hope this helps (and I hope I am not wrong). :-)

forsdan · #4 Post by **forsdan** » Sat Feb 28, 2009 10:38 am

Dear mrm,

The 'Selective Dynamics' tag only locks the direct coordintes of the atoms and not the cartesian coordinates. This implies that you can't use this tag to minimize the c-axis with respect to an arbitrary constraint on the magnitude of the a,b lattice vectors.

cheers,
/Dan

<span class='smallblacktext'>[ Edited Sat Feb 28 2009, 11:40AM ]</span>