Why is the unit cell changing in the output file

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jaburt · #1 Post by **jaburt** » Fri Aug 12, 2005 1:56 pm

I have been running geometry optimizations for certain minerals and there are descrepancies between the volume and direct lattice vectors from the input file and those given in the output file. Before any iterations are run the unit cell parameters (direct lattice vectors) in the output file are different from those given in the POSCAR file. At the end of the run the direct lattice vectors have not changed, but in the CONTCAR file I am given my original unit cell parameters. Does anyone why this is? Is VASP altering the volume of my unit cell before the geometry optimization?

Thanks

Jason

bruent · #2 Post by **bruent** » Mon Aug 15, 2005 8:14 am

May I see your OUTCAR and POSCAR?

jaburt · #3 Post by **jaburt** » Wed Aug 17, 2005 8:41 pm

Here is the unit cell matrix from the OUTCAR file:

7.092920653 0.000000000 0.000000000
-2.158130545 7.511449542 0.000000000
-1.068749324 -0.306057406 5.433820096

Here is the unit cell matrix from the CONTCAR file (same as POSCAR):

7.1262000068047939 -0.0000000002506637 -0.0000000000675099
-2.1682563023359163 7.5466925965608587 -0.0000000002786286
-1.0737638010662385 -0.3074934000354140 5.4593150973523219

I know the difference isn't much, but why aren't they the same.