7.2. Tutorial

In this tutorial, we explain through a sample calculation of the 8-site Hubbard model on the square lattice.

7.2.1. Run HPhi/vmc.out

  • For HPhi++

    We calculate the ground state and the correlation function with the following input file

    a0w = 2
    a0l = 2
    a1w = -2
    a1l = 2
    model="Hubbard"
    method="CG"
    lattice="square"
    t=1.0
    U=8.0
    nelec = 8
    2Sz=0
    
    $ HPhi -s input
    
  • For mVMC

    First, we optimize the trial wavefunction with the following input

    a0w = 2
    a0l = 2
    a1w = -2
    a1l = 2
    model="Hubbard"
    lattice="square"
    t=1.0
    U=8.0
    nelec = 8
    2Sz=0
    
    $ vmc.out -s input
    

    We add the following line to the input file to compute the correlation function.

    NVMCCalMode = 1
    

    Compute the correlation function.

    $ vmc.out -s input output/zqp_opt.dat
    

Then the one- and two-body correlation function are written to files in the output/ directory.

Related files

7.2.2. Fourier transformation of correlation functions

Perform the Fourier transformation of the correlation function by using the utility greenr2k.

$ echo "4 20
G 0 0 0
X 0.5 0 0
M 0.5 0.5 0
G 0 0 0
16 16 1" >> geometry.dat
$ greenr2k namelist.def geometry.dat

Then the Fourier-transformed correlation functions are written to a file in output/.

Related files

7.2.3. Display correlation functions

Plot the correlation function in the k space by using gnuplot.

load "kpath.gp"
plot "output/zvo_corr_eigen0.dat" u 1:12 w l
../_images/corplot.png

Fig. 7.1 Figure 6: The spin-spin correlation \(\langle{\bf S}_{\bf k}\cdot{\bf S}_{\bf k}\rangle\) (Column 12).

Related files