B3LYP simulations for CNTs

[manas_pratap]

Hi all,

I've neem trying to obtain a bandstructure using B3LYP for a few CNTs, but I have been unsuccessful so far.
I first do a standard DFT SC calculation to obtain the CHGCAR and WAVECAR files. I then copy these files into the B3LYP folder, where I create a KPOINTS file suitable for HF calculations (weighted and zero-weighted kpoints)
I then use the following INCAR file for the calculation. However, my bandstructure does not look like a bandstructure at all.

I would be grateful for any advice on this matter. Thank you!

Code: Select all

ISMEAR =  0
SIGMA  =  0.05
LHFCALC = T
GGA = B3
AEXX = 0.2
AGGAX = 0.72
AGGAC = 0.81
ALDAC = 0.19
ALGO = Damped
TIME = 0.4
LREAL = AUTO
EDIFF = 1.0E-07
ENCUT = 600.00
KPAR = 3
NCORE = 8
NBANDS = 256

I've considered NBANDS = 256 since I have 32 atoms in my system, all carbon atoms.

POSCAR -

Code: Select all

CNT_8_0
    1.0
            21.29400000 0.00000000 0.00000000 
            0.00000000 21.29400000 0.00000000 
            0.00000000 0.00000000 4.26000000 
  C
  32
Direct
        0.35222061 0.50000000 0.16666667      	#	1      	C
        0.35222061 0.50000000 0.83333333      	#	2      	C
        0.64777939 0.50000000 0.83333333      	#	3      	C
        0.64777939 0.50000000 0.16666667      	#	4      	C
        0.50000000 0.64777939 0.83333333      	#	5      	C
        0.50000000 0.35222061 0.16666667      	#	6      	C
        0.50000000 0.64777939 0.16666667      	#	7      	C
        0.50000000 0.35222061 0.83333333      	#	8      	C
        0.55655273 0.63653036 0.66666667      	#	9      	C2
        0.55655273 0.36346964 0.33333333      	#	10     	C2
        0.44344727 0.63653036 0.33333333      	#	11     	C2
        0.44344727 0.36346964 0.66666667      	#	12     	C2
        0.36346964 0.44344727 0.33333333      	#	13     	C2
        0.36346964 0.55655273 0.66666667      	#	14     	C2
        0.63653036 0.44344727 0.66666667      	#	15     	C2
        0.63653036 0.55655273 0.33333333      	#	16     	C2
        0.44344727 0.36346964 0.33333333      	#	17     	C2
        0.44344727 0.63653036 0.66666667      	#	18     	C2
        0.55655273 0.36346964 0.66666667      	#	19     	C2
        0.55655273 0.63653036 0.33333333      	#	20     	C2
        0.63653036 0.55655273 0.66666667      	#	21     	C2
        0.63653036 0.44344727 0.33333333      	#	22     	C2
        0.36346964 0.55655273 0.33333333      	#	23     	C2
        0.36346964 0.44344727 0.66666667      	#	24     	C2
        0.60449581 0.60449581 0.83333333      	#	25     	C3
        0.60449581 0.39550419 0.16666667      	#	26     	C3
        0.39550419 0.60449581 0.16666667      	#	27     	C3
        0.39550419 0.39550419 0.83333333      	#	28     	C3
        0.39550419 0.39550419 0.16666667      	#	29     	C3
        0.39550419 0.60449581 0.83333333      	#	30     	C3
        0.60449581 0.39550419 0.83333333      	#	31     	C3
        0.60449581 0.60449581 0.16666667      	#	32     	C3

[manuel_engel1]

Hi,

Thanks for reaching out. I will try to assist you as best as I can. To do that, I would like to ask a few clarifying questions first:

• When you say that you want to obtain a band structure, do you mean a band-structure plot along high-symmetry lines?

• What exactly does not look right about your band structure? What are your expectations?

• Do you obtain a good band structure when you do regular DFT instead of hybrids/HF?

• Could you please upload a minimum working example including the relevant input and output files according to the forum posting guidelines? I would like to inspect your calculation and be able to reproduce it if necessary.

[manas_pratap]

Hello, thank you for responding.

1. Yes, I mean a band-structure plot along high-symmetry lines. However, since transport in CNTs are along one direction only, I would need the high-symmetry lines in that particular direction.

2. The valence bands are looping. Here's an example of what's wrong with my bandstructure -

3. I get a reasonable bandstructure when I do standard DFT, as well as with HSE06. My problem in particular lies with the B3LYP calculation.

Here's a minimum working example. I will also include the input files for the B3LYP calculation, but these take a very long time to finish.
I am grateful for any advice you may have.

Thank you.

[manuel_engel1]

Thank you for providing the additional information. Unfortunately, I'm still not sure what is causing the issue you are facing. Could you please also share the OUTCAR files of the individual runs, in particular the band-structure calculation with B3LYP?

Do you copy the output of the B3LYP calculation to the bandstructure directory and rerun non-selfconsistently, the same way you do it for standard DFT?

I am not an expert when it comes to CNTs but I don't see a reason why B3LYP wouldn't work for this system.

[manas_pratap]

Hello,
Sorry it seems I forgot to include the OUTCAR files.
I'm attaching the files here.

For B3LYP calculations, I do the same procedure as with HSE06, where I copy the output from the self consistent run into the bandstructure folder.

[manuel_engel1]

No worries, thank you for uploading the file.

I have quickly looked at the OUTCAR file included in the Standard_bandstructure directory (which seems to be the B3LYP band-structure calculation along a k-path). When plotting the eigenvalues directly from the OUTCAR, I get a reasonable band-structure plot that looks nothing like the image you have posted earlier. This seems to suggest that there is nothing wrong with the calculation but with the processing of the output. I think we are getting much closer to the answer. Here are some things to consider:

• How do you extract/plot the band structure (scripts, py4vasp, etc.)?

• From which output file are you reading the band structure (OUTCAR, EIGENVAL, PROCAR, vasprun.xml, vaspout.hdf5, etc.)?

• Are you able to confirm that the energies as listed on the OUTCAR or EIGENVAL files are OK? Or do they show the same strange behavior?

In the case that you are unfamiliar with the OUTCAR file, the relevant section starts like this:

Code: Select all

 E-fermi :  -2.9683     XC(G=0):  -3.4468     alpha+bet : -2.8602

 val. band max:       -2.9803326213   @ k =   0.0000   0.0000   0.1050
 cond. band min:      -2.9614155711   @ k =   0.0000   0.0000   0.2101
 fundamental gap:      0.0189170503
 Fermi energy:        -2.9682526466

 k-point     1 :       0.0000    0.0000    0.0000
  band No.  band energies     occupation
      1     -22.1627      2.00000
      2     -20.3023      2.00000
      3     -20.3023      2.00000
      4     -16.7842      2.00000

and it continues to list all k-points and bands.