mirror of
https://github.com/TREX-CoE/qmc-lttc.git
synced 2024-11-03 20:54:12 +01:00
49 lines
1.2 KiB
Fortran
49 lines
1.2 KiB
Fortran
double precision function gaussian(r)
|
|
implicit none
|
|
double precision, intent(in) :: r(3)
|
|
double precision, parameter :: norm_gauss = 1.d0/(2.d0*dacos(-1.d0))**(1.5d0)
|
|
gaussian = norm_gauss * dexp( -0.5d0 * (r(1)*r(1) + r(2)*r(2) + r(3)*r(3) ))
|
|
end function gaussian
|
|
|
|
|
|
subroutine gaussian_montecarlo(a,nmax,energy)
|
|
implicit none
|
|
double precision, intent(in) :: a
|
|
integer*8 , intent(in) :: nmax
|
|
double precision, intent(out) :: energy
|
|
|
|
integer*8 :: istep
|
|
|
|
double precision :: norm, r(3), w
|
|
|
|
double precision, external :: e_loc, psi, gaussian
|
|
|
|
energy = 0.d0
|
|
norm = 0.d0
|
|
do istep = 1,nmax
|
|
call random_gauss(r,3)
|
|
w = psi(a,r)
|
|
w = w*w / gaussian(r)
|
|
norm = norm + w
|
|
energy = energy + w * e_loc(a,r)
|
|
end do
|
|
energy = energy / norm
|
|
end subroutine gaussian_montecarlo
|
|
|
|
program qmc
|
|
implicit none
|
|
double precision, parameter :: a = 1.2d0
|
|
integer*8 , parameter :: nmax = 100000
|
|
integer , parameter :: nruns = 30
|
|
|
|
integer :: irun
|
|
double precision :: X(nruns)
|
|
double precision :: ave, err
|
|
|
|
do irun=1,nruns
|
|
call gaussian_montecarlo(a,nmax,X(irun))
|
|
enddo
|
|
call ave_error(X,nruns,ave,err)
|
|
print *, 'E = ', ave, '+/-', err
|
|
end program qmc
|