[Q-e-developers] ibrav = 5, in INPUT_PW.def

[nisihara225 at gmail.com]

Dear Paolo,

trigonal lattice (ibrav = 5) has same angles alpha = beta = gamma.
However, only cos(gamma) or cosab is copied to celldm(4), as the source file (cell_base.f90, line211-240):

     IF ( celldm(1) == 0.D0 .and. a /= 0.D0 ) THEN
        !
        celldm(1) = a / bohr_radius_angs
        celldm(2) = b / a
        celldm(3) = c / a
        IF ( (ABS(cosab) > 1.0_dp) .OR. (ABS(cosac) > 1.0_dp) .OR. &
             (ABS(cosbc) > 1.0_dp) ) CALL errore ('cell_base_init',&
                         'incorrect values for cosab, cosac, cosbc',1)
        !
        IF ( ibrav == 14 ) THEN
           !
           ! ... triclinic lattice
           !
           celldm(4) = cosbc
           celldm(5) = cosac
           celldm(6) = cosab
           !
        ELSE IF ( ibrav ==-12 ) THEN
           !
           ! ... monoclinic P lattice, unique axis b
           !
           celldm(5) = cosac
           !
        ELSE
           !
           ! ... trigonal and monoclinic lattices, unique axis c
           !
           celldm(4) = cosab
           !
        ENDIF

Then, users have to set gamma (cosab) in an input-file, not alpha (cosbc) or beta (cosac).

Regards,
Satomichi


差出人: Paolo Giannozzi
送信日時: 2017年5月2日 23:52
宛先: General discussion list for Quantum ESPRESSO developers
件名: Re: [Q-e-developers] ibrav = 5, in INPUT_PW.def

Hi

ibrav=5 is the rhombohedral (or trigonal) lattice, having the three
angles alpha=beta=gamma/=90. Is there any rule or tradition according
to which such angle should be called gamma instead of alpha?

Paolo


On Mon, May 1, 2017 at 8:25 AM,  <nisihara225 at gmail.com> wrote:
> Dear QE-developers,
>
>
>
> INPUT_PW.def says that celldm(4) = cos(alpha) when ibrav = +-5.
>
> However, it may be celldm(4) = cos(gamma) to be correct.
>
>
>
> Regards,
>
> Satomichi Nishihara
>
>
>
>
> _______________________________________________
> Q-e-developers mailing list
> Q-e-developers at qe-forge.org
> http://qe-forge.org/mailman/listinfo/q-e-developers
>



-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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