Calculate spin density and save it to SPIN_DENSITY.vasp

spin_density.py

#!/usr/bin/env python3

from ase.calculators.vasp import VaspChargeDensity

print("READING CHGCAR ...")
chgcar = VaspChargeDensity("CHGCAR")
assert chgcar.is_spin_polarized()

if len(chgcar.chgdiff) == 1:
    spin_density = chgcar.chgdiff[0].copy()
    pass
elif len(chgcar.chgdiff == 3):
    spin_density = chgcar.chgdiff[-1].copy()
    pass
else:
    raise ValueError("Invalid CHGCAR")
    pass

chgcar.chgdiff = []
chgcar.chg = [spin_density]

print("WRITING SPIN_DENSITY.vasp")
chgcar.write("SPIN_DENSITY.vasp", format='chg')

spin_density_specificband.py

#!/usr/bin/env python3

from ase.calculators.vasp import VaspChargeDensity
from argparse import ArgumentParser

def calc_spin_density(fname_up, fname_dn, prefix):
    up = VaspChargeDensity(fname_up)
    dn = VaspChargeDensity(fname_dn)

    up.chg[0][...] -= dn.chg[0]
    up.write(prefix + "_spinden.vasp")

def parse_args():
    parser = ArgumentParser(
        description="A tool to calculate spin density with given spin up and spin down densities.",
        add_help=True)
    parser.add_argument("spin_up", type=str, action="store",
                        help="Spin up density file")
    parser.add_argument("spin_dn", type=str, action="store",
                        help="Spin down density file")
    parser.add_argument("prefix", type=str, nargs="?",
                        help="Prefix of output filename", default="rsgrad")
    return parser.parse_args()


if '__main__' == __name__:
    args = parse_args()
    calc_spin_density(args.spin_up, args.spin_dn, args.prefix)