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