1
0
mirror of https://github.com/TREX-CoE/qmc-lttc.git synced 2024-07-16 08:00:45 +02:00
qmc-lttc/vmc.f90

46 lines
1.1 KiB
Fortran

subroutine variational_montecarlo(a,dt,nmax,energy)
implicit none
double precision, intent(in) :: a, dt
integer*8 , intent(in) :: nmax
double precision, intent(out) :: energy
integer*8 :: istep
double precision :: norm, r_old(3), r_new(3), d_old(3), sq_dt, chi(3)
double precision, external :: e_loc
sq_dt = dsqrt(dt)
! Initialization
energy = 0.d0
norm = 0.d0
call random_gauss(r_old,3)
do istep = 1,nmax
call drift(a,r_old,d_old)
call random_gauss(chi,3)
r_new(:) = r_old(:) + dt * d_old(:) + chi(:)*sq_dt
norm = norm + 1.d0
energy = energy + e_loc(a,r_new)
r_old(:) = r_new(:)
end do
energy = energy / norm
end subroutine variational_montecarlo
program qmc
implicit none
double precision, parameter :: a = 1.2d0
double precision, parameter :: dt = 0.2d0
integer*8 , parameter :: nmax = 100000
integer , parameter :: nruns = 30
integer :: irun
double precision :: X(nruns)
double precision :: ave, err
do irun=1,nruns
call variational_montecarlo(a,dt,nmax,X(irun))
enddo
call ave_error(X,nruns,ave,err)
print *, 'E = ', ave, '+/-', err
end program qmc