Dear researchers,
I'm new to Quantum ESPRESSO software and I have a question regarding the input file for 2D vanadium carbide quantum dots. I've prepared one using atomic positions obtained from the Materials Project and VESTA software. However, the output does not contain relaxed atomic positions. Also, the energy does not converge in scf calculation. What mistakes have I made in this input file?
Could someone with expertise in this area kindly review my input file and provide feedback? I'm particularly interested in ensuring the accuracy of the data and parameters included, especially given the absence of relaxed atomic positions in the output.
Thank you in advance for your assistance
&CONTROL
title = 'v2c'
calculation = 'vc-relax'
restart_mode = 'from_scratch'
outdir = '/root/v2c/relax/'
wfcdir = '/root/v2c/relax/'
pseudo_dir = '/root/v2c/'
prefix = 'v2c'
tstress = .true.
tprnfor = .true.
/
&SYSTEM
ibrav = 8
A = 26.0
B = 20.0
C = 11.0
nat = 54
ntyp = 2
ecutwfc = 48
ecutrho = 631
occupations = 'smearing'
degauss = 0.02
smearing = 'gaussian'
/
&ELECTRONS
electron_maxstep = 100
conv_thr = 1.D-6
mixing_beta = 0.7
tqr = .true.
/
&IONS
/
&CELL
cell_dynamics = 'bfgs'
cell_dofree = 'y'
/
ATOMIC_SPECIES
C 12.00000 C.pbe-n-kjpaw_psl.1.0.0.UPF
V 50.9451 V.pbe-spnl-kjpaw_psl.1.0.0.UPF
ATOMIC_POSITIONS (angstrom)
V 4.418456 1.700666 5.726196
V 2.945637 4.251663 5.726196
V 1.472818 6.802660 5.726196
V 7.364093 1.700666 5.726196
V 5.891274 4.251663 5.726196
V 4.418456 6.802660 5.726196
V 10.309731 1.700666 5.726196
V 8.836912 4.251663 5.726196
V 7.364093 6.802660 5.726196
V 13.255369 1.700666 5.726196
V 11.782550 4.251663 5.726196
V 10.309731 6.802660 5.726196
V 16.201007 1.700666 5.726196
V 14.728188 4.251663 5.726196
V 13.255369 6.802660 5.726196
V 5.891277 0.850332 3.548618
V 4.418458 3.401329 3.548618
V 2.945639 5.952326 3.548618
V 8.836915 0.850332 3.548618
V 7.364096 3.401329 3.548618
V 5.891277 5.952326 3.548618
V 11.782553 0.850332 3.548618
V 10.309734 3.401329 3.548618
V 8.836915 5.952326 3.548618
V 14.728191 0.850332 3.548618
V 13.255372 3.401329 3.548618
V 11.782553 5.952326 3.548618
V 17.673829 0.850332 3.548618
V 16.201010 3.401329 3.548618
V 14.728191 5.952326 3.548618
C 4.418457 0.000000 4.637407
C 2.945638 2.550997 4.637407
C 1.472819 5.101995 4.637407
C 0.000000 7.652992 4.637407
C 7.364095 0.000000 4.637407
C 5.891276 2.550997 4.637407
C 4.418457 5.101995 4.637407
C 2.945638 7.652992 4.637407
C 10.309733 0.000000 4.637407
C 8.836914 2.550997 4.637407
C 7.364095 5.101995 4.637407
C 5.891276 7.652992 4.637407
C 13.255371 0.000000 4.637407
C 11.782552 2.550997 4.637407
C 10.309733 5.101995 4.637407
C 8.836914 7.652992 4.637407
C 16.201009 0.000000 4.637407
C 14.728190 2.550997 4.637407
C 13.255371 5.101995 4.637407
C 11.782552 7.652992 4.637407
C 19.146647 0.000000 4.637407
C 17.673828 2.550997 4.637407
C 16.201009 5.101995 4.637407
C 14.728190 7.652992 4.637407
K_POINTS automatic
1 1 1 1 1 1
Hello Mahya Aminrayai Jezeh
In Quantum ESPRESSO, inputs file can be a trouble. Let's start from the easiest, which is the SCF calculation. If your system's energy doesn't converge, this is where we start. I can try to replicate your calculation, and check what could be wrong. But in advance, you must increase k-points, like 4 4 1 1 1 0. I have been trying to calculate energy of surfaces, and tutorials say that you must put 1 in Z direction. So, my first guess is that you must achieve a convergence in SCF through a higher k-points mesh, and then we can set an strategy to optimize.
Best regards,
Ricardo Tadeu.
Well, I just tried to use the input as you described, and I really think we can create a much simpler input. The cell is unnecessarily big and the calculation is way too expensive. So, I will try to come with a simplified structure. Is this vanadium carbide like this structure in the figure?
Hello Ricardo Tadeu Maia
Thanks for your attention
In fact, I think this figure is not correct because the vanadiums are placed in one plane and the carbons in another plane, while in this structure they are placed in one plane.
Ok, I understood. Do you have a CIF file of it? I got this structure from a CIF file deposited in Crystallography Open Database, that's why I asked. Once we have the correct structure, we can make the input.
I used this site to get the atomic positions of V2C "https://next-gen.materialsproject.org/materials/mp-1094023?formula=V2C", but because I actually want one layer of these atoms, I deleted the rest.
I will try to make a model for this structure, and then make a test calculation
Hello.
I managed to make this slab with a single layer. Look how much simpler this is compared with the input you described. Please check if you approve this, and then you could try an optimization based in this input. I can show how I created this slab if you want
Hello,
Yes, this file looks correct, but I plan to work on quantum dot, so I tried to define a unit cell in my file.
Well, quantum dots are very small particles that "reverts" the band theory of solids. In a "normal" solid, there are so many atoms that their orbitals energy levels merge, and form the bands. In quantum dots, it's the opposite, you try to reduce the particles so they don't have that much atoms, and you will "unmerge" the bands, going back to splitted orbitals levels. I don't know how we could do it in QE, but you said you needed a single layer of atoms, didn't you?