Calculating DOS and PDOS

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Calculating DOS and PDOS#

DOS#

ABACUS can calculate the density of states (DOS) of the system, and the examples can be found in examples/dos. We first, do a ground-state energy calculation with one additional keyword “out_chg” in the INPUT file:

out_chg              1

this will produce the converged charge density, which is contained in the file chg.cube. Then, use the same STRU file, pseudopotential file and atomic orbital file (and the local density matrix file occ_mat.txt if DFT+U is used) to do a non-self-consistent calculation. In this example, the potential is constructed from the ground-state charge density from the proceeding calculation. Now the INPUT file is like:

INPUT_PARAMETERS
#Parameters (General)
suffix Si2_diamond
ntype 1
nbands 8
calculation nscf
basis_type lcao
read_file_dir   ./

#Parameters (Accuracy)
ecutwfc 60
symmetry 1
scf_nmax 50
scf_thr 1.0e-9
pw_diag_thr 1.0e-7

#Parameters (File)
init_chg file
out_dos 1
dos_sigma 0.07

Some parameters in the INPUT file are explained:

  • calculation

    choose which kind of calculation: scf calculation, nscf calculation, structure relaxation or Molecular Dynamics. Now we need to do one step of nscf calculation. Attention: This is a main variable of ABACUS, and for its more information please see the here.

  • pw_diag_thr

    threshold for the CG method which diagonalizes the Hamiltonian to get eigenvalues and eigen wave functions. If one wants to do nscf calculation, pw_diag_thr needs to be changed to a smaller account, typically smaller than 1.0e-3. Note that this parameter only apply to plane-wave calculations that employ the CG or Davidson method to diagonalize the Hamiltonian. For its more information please see the here.

    For LCAO calculations, this parameter will be neglected !

  • init_chg

    the type of starting density. When doing scf calculation, this variable can be set ”atomic”. When doing nscf calculation, the charge density already exists(eg. in chg.cube), and the variable should be set as ”file”. It means the density will be read from the existing file chg.cube. For its more information please see the here.

  • out_dos

    output density of state(DOS). The unit of DOS is (number of states)/(eV * unitcell). For its more information please see the here.

  • dos_sigma

    the gaussian smearing parameter(DOS), in unit of eV. For its more information please see the here.

  • read_file_dir

    the location of electron density file. For its more information please see the here.

To have an accurate DOS, one needs to have a denser k-point mesh. For example, the KPT file can be set as:

K_POINTS
0
Gamma
8 8 8 0 0 0

Run the program, and you will see a file named doss1g1.txt in the output directory. The columns are: energy(eV), dos (number of states in each energy bin), dos_int (integrated DOS), dos_smear(1/eV) (Gaussian-smeared DOS), dos_smear_int (integrated smeared DOS). Plot the file with graphing software, and you’ll get the DOS.

The dos column is a raw per-bin histogram, while dos_smear is the physically meaningful density of states in 1/eV. The abacus-plot tool plots dos_smear by default; set "smearing": false in its config.json to plot the raw histogram instead, or apply your own smearing to the raw column with abacus_plot.utils.gaussian_smearing. For nspin=2, two files (doss1*/doss2*) are written, one per spin channel; the tool pairs them automatically whether you pass either file, a directory, or a list of both files. For nspin=4, a single spinor-summed file is written.

#   energy(eV)           dos        dos_int  dos_smear(1/eV)  dos_smear_int
      -5.49311       0.0518133       0.0518133       0.0518133       0.0518133
      -5.48311       0.0641955        0.116009       0.0641955        0.116009
      -5.47311       0.0779299        0.193939       0.0779299        0.193939
      ...

PDOS#

Along with the DOS files, we also produce the projected density of states (PDOS) in files named pdoss{spin}g{geom}.txt (e.g., pdoss1g1.txt).

The PDOS file uses a plain-text format. Each row corresponds to one energy point and one atom. Columns: energy(eV), atom (1-based), species, then pdos values ordered as s(1), p(3), d(5), f(7), etc. Zeta components are summed, and values below 1e-6 are zeroed out.

# istep: 1
# npoints: 2736
# energy(eV)  atom  species  pdos(1/eV), columns: s(m=0) p(m=0,+1,-1) d(m=0,+1,-1,+2,-2) f(m=0,+1,-1,+2,-2,+3,-3)
  -55.607730    1     Fe    0.000000    0.000000    0.000000    0.000000    0.000000    0.000000    0.000000    0.000000    0.000000
  ...

The # istep: line is only present for geometry-optimization (istep) output. Within each angular momentum l, the 2l+1 columns follow the magnetic-quantum-number order m = 0, +1, -1, +2, -2, ....

For nspin=2, two files are written (pdoss1* and pdoss2*), one per spin channel. For nspin=4, the two spinor components are summed into a single file. The unit of PDOS is also (number of states)/(eV * unitcell).

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