4.6.2 DOS, wave functions
The main task of this section is to calculate the density of states (DOS) of the system. At first, do a groundstate energy calculation as in 4.6.1 and get the converged charge density, which is contained in the file SPIN1_CHG. Next, do a nonselfconsistent calculation. In this section the potential should be constructed from the groundstate 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
#Parameters (Accuracy)
ecutwfc 50
symmetry 1
niter 50
dr2 1.0e9
ethr 1.0e7
#Parameters (File)
start_charge file
out_dos 1
dos_sigma 0.07
#Parameters (Smearing)
smearing gaussian
sigma 0.02
New parameters in the INPUT file are:
• 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 Appendix 5.1.
• ethr threshold for the CG method which digonalizes the Hamiltonian to get eigenvalues and eigen wave functions. If one wants to do nscf calculation, ethr needs to be changed to a smaller account, typically smaller than 1.0e3. Note that this parameter only apply to planewave calculations that employ the CG method to diagonalize the Hamiltonian. For LCAO calculations, this parameter will be neglected !
• start_charge 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 SPIN1_CHG), and the variable should be set as ”file”. It means the density will be read from the existing file SPIN1_CHG. For more information please see Appendix 5.1.
• out_dos output density of state(DOS).
• dos_sigma the gaussian smearing parameter(DOS).
To have an accurate DOS, one needs to have a denser kpoint 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 DOS1_smearing.dat in the output directory. Next, plot file DAT with drawing software, and you’ll get the DOS.
