Using the lattice custom command for hcp structure

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1

Dear Steve,

On which base should I set my a1 & a2 & a3 for building a non-ideal hcp by lattice custom? for hcp there is:
a1 = 1 0 0, a2 = 0 sqrt(3) 0, and a3 = 0 0 sqrt(8/3) .
when sqrt(8/3)=1.63 belongs to the c/a ratio of an ideal hcp. So to set a non-ideal hcp by the lattice custom command, should I use my specific c/a which is equal to 1.58 instead of sqrt(8/3)? moreover, is sqrt(3)=1.73 a fixed value for a2 in all non-ideal fcc beacase of the only one degree of freedom for hcp?
I have a=2.95 , c=4.68 , c/a=1.58, could you tell me whether or not it is true?

lattice custom 1 a1 2.97 0.0 0.0 a2 0.0 1.73 0.0 a3 0.0 0.0 1.58 &
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

Thank you,
Nazanin

2

I have a=2.95 , c=4.68 , c/a=1.58, could you tell me whether or not it is true?

If this is what you want, then use:

lattice custom 1 a1 2.95 0.0 0.0 a2 0.0 whatever 0.0 a3 0.0 0.0 4.68

The custom command is setting a,b,c directly. I.e. the 3rd argument
of a3 is c. The 1st arg of a1 is a. The ratios will
be whatever you set them to be.

Steve