[Pw_forum] ?spam? Re: vc-relax - negative and non-zero cell parameters
Максим Попов
max.n.popov at gmail.com
Fri May 20 15:22:25 CEST 2011
Dear Christopher,
The structure is chosen at random, as I simply wish to test the vc-relax
> procedure, so I don't expect it to have a particular symmetry, although in
> general, I am dealing with clusters of low symmetry anyway.
>
>
If you are dealing with clusters, then there is no utility of vc-relax for
you.
> My problem is that it makes no sense to me that off diagonal elements can
> be non-zero, when they are relative. How can one have a value 0.000341145 x
> 0 (in the case of element (1,2))? This, I do not understand.
>
> Furthermore, what would a negative relative parameter mean?
> I suspect I am misinterpreting the meaning of these alat cell parameter
> matrices, but I'm not sure how.
>
The matrix, you see in the output, is Bravais matrix, i.e. a matrix, where
the cartesian coordinates of a
unit cell vectors are packed in rows.
The notation:
CELL_PARAMETERS (alat= 30.23000000)
1.003485881 0.000341145 -0.000166335
0.000341140 1.002476151 0.000847099
-0.000166325 0.000846982 1.001936910
means that Bravais matrix is:
{ 1.003485881 0.000341145 -0.000166335 }
{ 0.000341140 1.002476151 0.000847099 } times alat =
{ -0.000166325 0.000846982 1.001936910 }
{ 30.3354 0.0103 -0.0050 }
{ 0.0103 30.3049 0.0256 }
{ -0.0050 0.0256 30.2886 }
Hope, it helps.
--
Best regards, Max Popov
Ph.D. student
Materials center Leoben (MCL), Leoben, Austria.
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