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!! using dftd3 API to get pressure by changing the alat
program test_code
use dftd3_api
use cell_base
implicit none
integer,parameter :: wp = kind(1.0d0)
integer :: natoms, i, j
real(wp) :: a0,ap,am,edisp1,edisp2
real(wp), allocatable :: coords(:,:), coords0(:,:)
real(wp), allocatable :: tau(:,:)
real(wp), allocatable :: test_force(:,:)
real(wp), dimension(3,3) :: latvecs, latvecs0
character*2, allocatable :: typatom(:)
type(dftd3_input) :: input
type(dftd3_calc) :: dftd3
integer,allocatable :: atnum(:)
real(wp) :: edisp, Ep, Em
real(wp) :: omega0, omega1, omega2
real(wp), allocatable:: grads(:,:)
real(wp), dimension(3,3) :: stress
real(wp), parameter :: delta = 0.001
real(wp) :: stress_num(3,3)
! ----- need to read: coordinates, atoms, lattice vectors
read(*,*) a0
read(*,*) latvecs(1,1), latvecs(2,1), latvecs(3,1)
read(*,*) latvecs(1,2), latvecs(2,2), latvecs(3,2)
read(*,*) latvecs(1,3), latvecs(2,3), latvecs(3,3)
latvecs0(:,:) = latvecs(:,:)
latvecs(:,:) = latvecs(:,:) * a0
a0=a0 ! * 1.8897261 !! API expects it in Ang, and auto-converts it to bohr.
!! The idea here was to have same input as for dftd3.f in
!! Grimme's original code. Now not used.
latvecs(:,:) = latvecs(:,:) ! * 1.8897261
call volume(a0, latvecs0(1,1), latvecs0(1,2), latvecs0(1,3), omega0 )
read(*,*) natoms
allocate(typatom(1:natoms))
typatom(:) = 'none'
allocate(coords(1:3, 1:natoms))
allocate(coords0(1:3, 1:natoms))
allocate(tau(1:3,1:natoms))
allocate(test_force(1:3,1:natoms))
allocate(atnum(1:natoms))
allocate(grads(1:3, 1:natoms))
do i=1, natoms
read(*,*) typatom(i), coords(1,i), coords(2,i), coords(3,i)
end do
do i=1,natoms
do j=1,3
coords(j,i)=coords(1,i)*latvecs0(j,1)+coords(2,i)*latvecs0(j,2)+coords(3,i)*latvecs0(j,3)
end do
end do
coords0(:,:) = coords(:,:)
coords(:,:)=coords(:,:)*a0
write(*,*)'coords in units of a0'
write(*,"(3ES20.12)") coords
stress(:,:)=0.0
stress_num(:,:)=0.0
input%threebody = .true.
input%numgrad = .false.
atnum(:) = get_atomic_number(typatom)
! initialize dftd3
call dftd3_init(dftd3, input)
! choose functional
call dftd3_set_functional(dftd3, func='pbe',version=3, tz=.false.)
tau(:,:) = coords(:,:)
write(*,*)'tau'
write(*,"(3ES20.12)") tau
write(*,*)
write(*,*) 'atomic numbers',atnum
write(*,*)
write(*,*) 'latvecs used for dftd3-API in units of a0'
write(*,"(3ES20.12)") latvecs
write(*,*)
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,edisp,grads,stress)
write(*,*)
write(*,*) 'edisp [Ry]',edisp*2.00
write(*,*)
write(*,*) 'forces from dftd3-API [Ha/au]'
write(*,"(3ES20.12)") grads
write(*,*)
write(*,*)"Forces calculated numerically: [Ha/au]"
do j=1,natoms
do i=1,3 ! x,y,z coordinates
tau(:,:) = coords(:,:)
tau(i,j) = coords(i,j) - (delta/a0)
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,edisp1)
tau(i,j) = coords(i,j) + (delta/a0)
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,edisp2)
test_force(i,j) = (edisp2 - edisp1)/(2.000000000000*delta/a0)
end do
write(*,*) test_force(1,j),test_force(2,j),test_force(3,j)
end do
write(*,*)
write(*,*) 'stress from dftd3-API [Ha/au^3]'
write(*,"(3ES20.12)") stress
write(*,*)
do i=1,3
do j=1,3
tau(:,:)=coords0(:,:)*a0
latvecs(:,:)=latvecs0(:,:) * a0
latvecs(j,i)=latvecs(j,i) + 0.0001
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,Ep)
latvecs(j,i)=latvecs(j,i) - 0.0002
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,Em)
stress_num(j,i)=(Ep - Em) / (0.0002)
end do
end do
write(*,*) 'numerical stress [Ha/au^3]'
write(*,"(3ES20.12)") 1.0/omega0 *(-matmul(stress_num,transpose(latvecs)))
write(*,*)
ap=a0+0.0001
latvecs(:,:)=latvecs0(:,:)*ap
tau(:,:) = coords0(:,:) * ap
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,Ep)
call volume(ap, latvecs0(1,1), latvecs0(1,2), latvecs0(1,3), omega2 )
am=a0-0.0001
latvecs(:,:)=latvecs0(:,:)*am
tau(:,:) = coords0(:,:) * am
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,Em)
call volume(am, latvecs0(1,1), latvecs0(1,2), latvecs0(1,3), omega1 )
write(*,*) 'omega =',omega0, omega2, omega1
write(*,*) 'dE / dV =', 1.0 * (Ep-Em)/(omega2-omega1)
write(*,*)
CALL recips(latvecs0(1,1),latvecs0(1,2),latvecs0(1,3),bg(1,1),bg(1,2),bg(1,3))
bg(:,:)=bg(:,:)
latvecs(:,:)=latvecs0(:,:) * a0
latvecs(1,1)=latvecs(1,1) + 0.0001
tau(:,:) = coords0(:,:) * a0
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,Ep)
latvecs(:,:)=latvecs0(:,:) * a0
latvecs(1,1)=latvecs(1,1)-0.0001
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,Em)
write(*,*) 'dE / dx =', (Ep - Em) / (0.0002)
latvecs(:,:)=latvecs0(:,:) *a0
latvecs(2,2)=latvecs(2,2) + 0.0001
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,Ep)
latvecs(:,:)=latvecs0(:,:) * a0
latvecs(2,2)=latvecs(2,2)-0.0001
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,Em)
write(*,*) 'dE / dy =', (Ep - Em) / (0.0002)
latvecs(:,:)=latvecs0(:,:) * a0
latvecs(3,3)=latvecs(3,3) + 0.0001
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,Ep)
latvecs(:,:)=latvecs0(:,:) * a0
latvecs(3,3)=latvecs(3,3) - 0.0001
call dftd3_pbc_dispersion(dftd3,tau,atnum,latvecs,Em)
write(*,*) 'dE / dz =', (Ep - Em) / (0.0002)
contains
function determinant(aa) result(det)
real*8, intent(in) :: aa(:,:)
real*8 :: det
det = aa(1,1) * (aa(2,2) * aa(3,3) - aa(3,2) * aa(2,3))&
& - aa(1,2) * (aa(2,1) * aa(3,3) - aa(3,1) * aa(2,3))&
& + aa(1,3) * (aa(2,1) * aa(3,2) - aa(3,1) * aa(2,2))
end function determinant
end program test_code
subroutine inv(x,a) !x is normal lat, a is lat^(-1)
IMPLICIT NONE
real*8, intent(in) :: x(3,3) !unitcell vectors in direct space
real*8, intent(out) :: a(3,3) !unitcell vectors in reciprocal space
integer i
real*8 det
a=0.0
det=x(1,1)*x(2,2)*x(3,3)+x(1,2)*x(2,3)*x(3,1)+x(1,3)*x(2,1)*&
x(3,2)-x(1,3)*x(2,2)*x(3,1)-x(1,2)*x(2,1)*x(3,3)-x(1,1)*&
x(2,3)*x(3,2)
a(1,1)=x(2,2)*x(3,3)-x(2,3)*x(3,2)
a(2,1)=x(2,3)*x(3,1)-x(2,1)*x(3,3)
a(3,1)=x(2,1)*x(3,2)-x(2,2)*x(3,1)
a(1,2)=x(1,3)*x(3,2)-x(1,2)*x(3,3)
a(2,2)=x(1,1)*x(3,3)-x(1,3)*x(3,1)
a(3,2)=x(1,2)*x(3,1)-x(1,1)*x(3,2)
a(1,3)=x(1,2)*x(2,3)-x(1,3)*x(2,2)
a(2,3)=x(1,3)*x(2,1)-x(1,1)*x(2,3)
a(3,3)=x(1,1)*x(2,2)-x(1,2)*x(2,1)
a=a/det
end subroutine inv
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