Water

In this example, how to draw orbital/wave function densities, i.e., square moduli of the wave functions, is described. We use a water molecule in a box as an example.

SCF calculation

First we obtain the self-consistent electron density and wave functions of water molecule by using the following input file:

WF_OPT     DAV
NTYP       2
NATM       3
GMAX        6.00
GMAXP      20.00
MIX_ALPHA   0.5
EDELTA      1.D-10
NEG        12
CELL       15.00 15.00 15.00  90.00  90.00  90.00
&ATOMIC_SPECIES
 H   12.000000 pot.H_lda1
 O   12.000000 pot.O_pbe1
&END
&ATOMIC_COORDINATES CARTESIAN
      1.453447222619      0.000000000000      1.124989276510    1    1    1
     -1.453447222619      0.000000000000      1.124989276510    1    1    1
      0.000000000000      0.000000000000      0.000000000000    1    1    2
&END

Wave function density plot

We then modify the input file (nfinp_mo) as:

TASK       PRTWFC
WF_OPT     DAV
NTYP       2
NATM       3
GMAX        6.00
GMAXP      20.00
MIX_ALPHA   0.5
EDELTA      1.D-10
NEG        12
CELL       15.00 15.00 15.00  90.00  90.00  90.00
&ATOMIC_SPECIES
 H   12.000000 pot.H_lda1
 O   12.000000 pot.O_pbe1
&END
&ATOMIC_COORDINATES CARTESIAN
      1.453447222619      0.000000000000      1.124989276510    1    1    1
     -1.453447222619      0.000000000000      1.124989276510    1    1    1
      0.000000000000      0.000000000000      0.000000000000    1    1    2
&END
&PLOT
 IKPT 1
 IBS  4
 IBE  5
 CHG_WFN
 ADD_SIGN
 FORMAT XSF
&END

Similar to the wave function plot, we use the option:

TASK      PRTWFC

and the following block is added to the input file to plot the wave function in real space:

&PLOT
 IKPT 1
 IBS  4
 IBE  5
 CHG_WFN
 ADD_SIGN
 FORMAT XSF
&END

In this case, we are going to plot 4th (HOMO) and 5th (LUMO) wave function densities. by using the keyword CHG_WFN, the wave function density is calculated (FORMAT CHARGE_XSF can be used instead). Furthermore, by using the option ADD_SIGN the sign of the wave function is added to the wave function density. Note that the sign is meaningful only at the Gamma-point.

By executing STATE by using the above input file, you may obtain the following files for the orbital densities:

nfwfn_kpt0001_band0004.xsf
nfwfn_kpt0001_band0005.xsf

The naming convention is:

nfwfn_kpt[kpoint_index]_band[band_index].xsf

By using VESTA the wave function densities for HOMO and LUMO can be visualized as: