Dear Dr. Lorenzo,
Thank you for your reply and the code. I am not familiar with
Fortran. I need to calculate the total force constant of the atom
numbered 205 (Mg). I can understand that each pair of atoms has a
force constant matrix with 9 elements, and for my case, for one
supercell, there are a total of {(205*2)*9}=3690 values of matrix
elements only related to the 205^th atom. I need the addition of all
of these from each pair of root mean square values. Is there any
direct way or any calculation in QE itself to find this?
Thanks,
Chirantan
Chirantan Pramanik
Postdoctoral Researcher
Dept. of Earth and Planetary Sciences
Weizmann Institute of Science
Rehovot, Israel
------------------------------------------------------------------------
*From:* users <[email protected]> on behalf of
Lorenzo Paulatto <[email protected]>
*Sent:* Tuesday, May 6, 2025 11:09 AM
*To:* [email protected] <[email protected]>
*Subject:* Re: [QE-users] Format of the interatomic force constant .fc
file
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On 05/05/2025 12:52, Chirantan Pramanik wrote:
Dear All,
I am stuck with the format of the interatomic force constant file
obtained by the q2r.x code. Below is a preview of the .fc file.
Please help me to understand the entries. I need the interatomic
force constant, suppose, only for the atom '205'.
Hello,
please note that force constants always act between two atoms,
assuming you know what you are doing, here is the subroutine that
reads the force constants stripped of all the parallel distribution
and ssafety checks, it is only a couple dozen liens of code. The
subroutine reads the force constants for a supercell of size
nr1×nr2×nr3, because of translational invariance, the first atom
(i,na) is always in the first unit cell (i.e. that with coordinates
0,0,0) while the second atom (j,nb) is in cell (nr1-1)*a1 + (nr2-1)*a2
+ (nr3-1)*a3. (Or maybe it is the second atom which is in cell 0,0,0,
I never remember).
Because in your case the cell is 1×1×1, it won't make any difference.
hth
!-----------------------------------------------------------------------
SUBROUTINEreadfc( flfrc, nr1, nr2, nr3, epsil, nat, &
ibrav, alat, at, ntyp, amass, omega, &
has_zstar, alph, read_lr)
!-----------------------------------------------------------------------
!
IMPLICITNONE
! I/O variable
CHARACTER(LEN=256) ::flfrc
CHARACTER(LEN=80) ::line
INTEGER::ibrav, nr1,nr2,nr3,nat, ntyp
REAL(DP) ::alat, at(3,3), epsil(3,3), alph
LOGICAL::has_zstar, read_lr
! local variables
INTEGER::i, j, na, nb, m1,m2,m3
INTEGER::ios, ibid, jbid, nabid, nbbid, m1bid,m2bid,m3bid
REAL(DP) ::amass(ntyp), amass_from_file, omega
INTEGER::nt
!
OPEN(unit=1,file=flfrc,status='old',form='formatted')
!
! Read cell parameters
READ(1,*) ntyp,nat,ibrav,(celldm(i),i=1,6)
if(ibrav==0) then
read(1,*) ((at(i,j),i=1,3),j=1,3)
end if
!
CALLlatgen(ibrav,celldm,at(1,1),at(1,2),at(1,3),omega)
alat =celldm(1)
at =at / alat ! bring at in units of alat
CALLvolume(alat,at(1,1),at(1,2),at(1,3),omega)
!
! read atomic types, positions and masses
!
ALLOCATE(atm(ntyp))
DOnt =1,ntyp
READ(1,*) i,atm(nt),amass_from_file ! type and mass
END DO
!
ALLOCATE(tau(3,nat), ityp(nat), zeu(3,3,nat))
!
DOna=1,nat
READ(1,*) i,ityp(na),(tau(j,na),j=1,3) ! positions of atoms in the cell
END DO
!
! read macroscopic variables
! (dielectric constant and effective charges)
!
alph =1.0_dp
READ(1,'(a)') line
READ(line,*,iostat=ios) has_zstar, alph
!
IF(has_zstar) THEN
READ(1,*) ((epsil(i,j),j=1,3),i=1,3)
DOna=1,nat
READ(1,*)
READ(1,*) ((zeu(i,j,na),j=1,3),i=1,3)
END DO
ELSE
zeu (:,:,:) =0.d0
epsil(:,:) =0.d0
END IF
!
READ(1,*) nr1,nr2,nr3
!
! read real-space interatomic force constants
!
ALLOCATE( frc(nr1,nr2,nr3,3,3,nat,nat) )
frc(:,:,:,:,:,:,:) =0.d0
ALLOCATE( frc_lr(nr1,nr2,nr3,3,3,nat,nat) )
frc_lr(:,:,:,:,:,:,:) =0.d0
DOi=1,3
DOj=1,3
DOna=1,nat
DOnb=1,nat
READ(1,*) ibid, jbid, nabid, nbbid
READ(1,*) (((m1bid, m2bid, m3bid, &
frc(m1,m2,m3,i,j,na,nb), &
m1=1,nr1),m2=1,nr2),m3=1,nr3)
END IF
END DO
END DO
END DO
END DO
!
CLOSE(unit=1)
!
RETURN
END SUBROUTINEreadfc
--
Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
phone: +33 (0)1 442 79822 / skype: paulatz
http://people.impmc.fr/lpaulatto/ <http://people.impmc.fr/lpaulatto/>
- https://anharmonic.github.io/ <https://anharmonic.github.io/>
23-24/423 B115, 4 place Jussieu 75252 Paris CX 05
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