About LATTICE_PARAMETER

[nkxirainbow]

Dear Professor:
I try to deal with monolayer graphene, which belongs to hexagonal system .
In my graphenen.band.in file of ESPRESSO-4.0.4, the structure is:
ibrav = 4,
celldm(1) = 4.609078567,
celldm(3) = 4.536272043,
But after I use p2y -S, I get the following lattice parameter in ns.db1 file.
LATTICE_PARAMETER = 4.609078, 3.991579, 20.90803 ;
LATTICE_VECTORS =
4.609078, -2.304539 0,
0, 3.991579, 0,
0, 0, 20.90803 ;

I think the lattice parameter should be LATTICE_PARAMETER= 4.609078 4.609078, 20.90803. Am I wrong?

By the way, I have attached the graphene.band.in and ns.db1 files.
Thank you very much:)

[andrea marini]

ibrav = 4,
celldm(1) = 4.609078567,
celldm(3) = 4.536272043,[/color]

But after I use p2y -S, I get the following lattice parameter in ns.db1 file.
LATTICE_PARAMETER = 4.609078, 3.991579, 20.90803 ;

I think the lattice parameter should be LATTICE_PARAMETER= 4.609078 4.609078, 20.90803. Am I wrong?

Yes, I think you're wrong. Reading the Doc/INPUT_PW.txt file in the PW source directory you see that in PW for simple hexagonal cells the three unit cell vectors are

v1 = a(1,0,0), v2 = a(-1/2,sqrt(3)/2,0), v3 = a(0,0,c/a).

and sqrt(3)/2*4.60907856 = 3.99157912706037685490. So everything seems correct to me.

Also bear in mind that the 3 dimensional LATTICE_PARAMETER array is used in Yambo to rescale internally the k-point coordinates and it has no special meaning if not to be the best choice to have k-pt coordinates written in a human readable format.

What you should check to see if the lattice structure is correct are the three A* vectors rescaled by the unit cell factors reported in any report file. For example of a report file in an hexagonal solid contains

Code: Select all

 Unit cell scaling factors [a.u.]:  4.71637   4.08450  12.17584

 Direct Lattice(DL) unit cell [iru]
 A1 = 1.000000  0.000000  0.000000
 A2 =-0.500000  1.000000  0.000000
 A3 = 0.000000  0.000000  1.000000

[nkxirainbow]

Dear Professor MARINI :

I got it.
Thanks a lot:P