Wigner/2D_eta0_triangle.f90
2021-03-11 12:28:00 +01:00

58 lines
992 B
Fortran

program triangle
implicit none
integer :: nside,nsite,nelec
integer :: ix,iy,iz,i
real*16 :: factor,bbfac
real*16 :: uee,ubb,eta0,aux
real*16 :: start,finish
real*16,allocatable :: sin2(:)
open(unit=10,file='input')
read(10,*) nside
close(10)
call cpu_time(start)
nsite = 2*nside
nelec = nside**2*2
!bbfac = 0.7839363355057699q0
bbfac = 0.78393636789823211548q0
write(6,*) "total number of electrons",nelec
allocate(sin2(nsite))
factor=acos(-1q0)/nsite
do i = 0, nsite-1
sin2(i+1) = (sin(factor*i))**2
enddo
uee = 0q0
do ix = 0, nsite-1
do iy = 0, nsite-1
if (ix+iy==0) cycle
if (mod(ix+iy,2)==1) cycle
aux = sqrt(sin2(ix+1)+3q0*sin2(iy+1))
uee = uee + 1q0/aux
enddo
enddo
factor=sqrt(acos(-1q0)/2q0)*3q0**(0.25q0)/nsite
uee=uee*factor
ubb = nelec*bbfac/nside
eta0 = uee - ubb
print*,'eta0 (in Ry and Ha) =', 2q0*eta0, eta0
deallocate(sin2)
call cpu_time(finish)
print '("Time = ",f12.3," seconds.")',finish-start
end program triangle