Regarding lattice command

Hello all,
I am using lattice custom command for Be atoms where a=2.2568, b=2.2568, c=3.539, c/a=1.5682 with hexagonal closed structure.

lattice custom 2.2568
a1 1.0 0.0 0.0&
a2 0.0 1.0 0.0&
a3 0.0 0.0 1.5682&
basis 0.0 0.0 0.0&
basis 0.5 0.5 0.0&
basis 0.5 0.25 0.5&
basis 0.0 0.75 0.5

In the manual lattice hcp has its different scaling values.
Here the atoms are placed a/q to hexagonal structure. Is it the right way?

You seem to be confused about what exactly is a hexagonal close-packed (HCP) crystal. This question is not very complicated, but outside the scope of this mailing list. You should do some reading on the subject, or try drawing it yourself. The following is a correct lattice custom command for your HCP crystal:

variable a equal 2.2568
variable b equal $asqrt(3.0)
variable c equal $a

lattice custom 1.0 a1 $a 0.0 0.0 &
a2 0.0 $b 0.0 &
a3 0.0 0.0 $c &
basis 0.0 0.0 0.0 &
basis 0.5 0.5 0.0 &
basis 0.0 0.33333333 0.5 &
basis 0.5 0.83333333 0.5


Thank you Aidan,

I got it.

Can i simply use lattice hcp 2.2568 in place of using lattice custom command for the same?

Not quite. lattice hcp will build a lattice with the ideal c/a ratio = sqrt(8/3). The Be lattice has a c/a ratio that is about 4% smaller. One solution is to follow lattice hcp with something like

change_box all z scale 0.96 remap

But I think an explicit specification of the Be lattice is the better solution, because it is more self-explanatory.


Thank you Aidan.