mirror of https://gitlab.com/QEF/q-e.git
87 lines
2.5 KiB
Fortran
87 lines
2.5 KiB
Fortran
!
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! Copyright (C) 2001-2010 Quantum ESPRESSO group
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! This file is distributed under the terms of the
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! GNU General Public License. See the file `License'
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! in the root directory of the present distribution,
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! or http://www.gnu.org/copyleft/gpl.txt .
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!
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! Calculate Free Energy F
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! Given phonon DOS, calculate F at various temperatures
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!
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program fqha
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!
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implicit none
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integer, parameter:: ndivx=10000
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real(8) :: dos(ndivx),nu(ndivx), T, a2,a3,Ftot,norm,F0
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real(8) :: de, de_, nu_,dos_
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integer :: i,ndiv
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character(len=256) :: filename
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!
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!
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write (*,"('File containing the dos >>> ',$)")
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read(*,'(a)') filename
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open(unit=1,file=filename,status='old')
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!
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de = 0d0
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do i=1,ndivx
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! nu(i) = frequencies (cm^{-1}), dos(i) in states/cm^{-1}
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read(1,*,end=10,err=20) nu(i),dos(i)
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if ( nu(i) < -1.d0 ) then
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stop ' wrong grid: omega < 0'
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else if ( nu(i) < 0.d0 ) then
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nu(i) = 0.d0
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end if
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if ( i > 1 ) then
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de = nu(i) - nu(i-1)
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if ( i > 2 ) then
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de_ = nu(i) - nu(i-1)
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if ( abs(de - de_) > 1.0d-4 ) stop ' wrong grid: not uniform'
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end if
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end if
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ndiv=i
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enddo
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read(1,*,end=10,err=20) nu_,dos_
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write(*,"('File read only up to line # ',i5)") ndivx
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10 close(1)
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write(*,"('Read ',i5,' lines; Delta e (cm^-1) =',f10.6)") ndiv,de
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! zero point energy : \sum (\hbar\omega/2) g(omega) d\omega
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F0 = 0.5 * de * dot_product ( dos(1:ndiv), nu(1:ndiv) )
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! result is in cm^{-1}, bring it to Ry
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F0 = F0 / 8065.5d0 / 13.6058d0
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! normalization check: \sum g(omega) d\omega = 3*Nat
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norm = sum (dos(1:ndiv)) * de
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write(*,"('Check: 3*Nat = ',f8.4,5x'zero-point energy (Ry)=',f15.8)") norm,F0
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write (*,"('Output file for the Free energy >>> ',$)")
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read(*,'(a)') filename
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if ( filename == '') then
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filename = 'fqha.out'
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write(*,"(' output to file ',a)") trim(filename)
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end if
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open(unit=1,file=filename,status='unknown')
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!
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1 continue
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write (*,"('Temperature (K) >>> ',$)")
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read (*,*,end=20,err=20) T
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if ( T < 0d0 ) then
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write(*,"('Incorrect T < 0, stopping')")
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go to 20
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end if
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! this is Kb in Ry/K
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a2=8.617d-5/13.6058d0
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! this is 1/Kb in cm^{-1}/K
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a3=1.0d0/8065.5d0/8.617d-5
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Ftot=0.0d0
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do i=1,ndiv
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if (T > 0.d0 .and. nu(i) > 0.d0) Ftot=Ftot+dos(i)*a2*T*log(1.0d0-exp(-a3*nu(i)/T))
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enddo
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Ftot=F0+Ftot*de
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write(*,"('T=',f8.2,'K, F(T)= ',f15.8,' Ry')") T,Ftot
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write(1,*) T,Ftot
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!
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go to 1
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20 close(1)
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!
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stop
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end program fqha
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!
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