Questions tagged [density-functional-theory]
For questions about simulations using Density Functional Theory.
234
questions
9
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2answers
249 views
Is there an energy gap correction factor that needs to be used in DFT calculations?
I am a beginner and have performed the DFT calculation in Quantum ESPRESSO for calculation of the direct and indirect bandgap of Silicon. I found the indirect bandgap to be 0.6551 eV. Now, I have ...
10
votes
1answer
252 views
Si energy band values are not matching with literature values
I have performed the DFT calculation for Silicon in Quantum ESPRESO. I have tried to calculate the electronic band structure, the shape of wiggles of bands are mostly matching but the energy values ...
4
votes
0answers
28 views
Is there any way to simulate the Polarization vs Electric Field loop of BaTiO3 using Quantum ESPRESSO?
I'm new to the Quantum ESPRESSO package. There are articles outlining the procedure of indirectly simulating the P-E loop of piezo-electric materials via berry phase calculations.One procedure is ...
6
votes
0answers
25 views
What's the crystal orbital Hamiltonian population?
What's the crystal orbital Hamiltonian population (COHP) or the crystal orbital overlap population (COOP)? What's the relation between the bandstructure or density of states (DOS) and COHP/COOP? Why ...
6
votes
1answer
138 views
When should “vc-relax” be performed over “relax” calculations in Quantum ESPRESSO?
I'm new to Quantum ESPRESSO and I have read that there are several scenarios when relax calculations are preferred over vc-relax calculations, for example in maintaining vacuum while modelling surface....
8
votes
1answer
55 views
How to do spin polarization calculations using Quantum ESPRESSO?
I am currently new to DFT calculations in Quantum ESPRESSO. Though, I have read some research papers for determining spin polarization and Half-metallicity in certain Heusler alloys. These research ...
8
votes
5answers
497 views
How to know optimal K-points grid values for good DFT calculation?
I am doing DFT calculations with pw.x executable in Quantum Espresso. For this we have to choose right K-points grid in order to perform error-less calculation. But I have no idea about how can I ...
7
votes
0answers
28 views
How does MBD (MBD-NL) differ from DFT-TS?
Is anyone familiar with the Tkatchenko's new MBD-NL method? How does it differ from DFT-TS? I couldn't understand everything from the paper.
8
votes
2answers
119 views
How to choose pseudopotential for DFT calculations in Quantum ESPRESSO?
I am a beginner and newly started running DFT calculations to find out the electronic band structure of certain materials in Quantum ESPRESSO. But we have to select the pseudopotential for running the ...
9
votes
1answer
71 views
How to build the matter modeling model with appropriate tools?
How to build the matter modeling model with appropriate tools?
When we perform matter simulation with first-principles calculation, building a reasonable model always be the very first and important ...
8
votes
2answers
106 views
Are meta-GGA functionals SCAN (and its variants) ok to use in planewave DFT with the PBE pseudopotentials?
The meta-GGA SCAN functional has been there for a while. Despite the lack of SCAN (ultrasoft/PAW) pseudopotentials, various works used it in plane-wave pseudopotential calculations with ...
10
votes
2answers
377 views
When should spin polarized calculations be done?
Should the presence of a d block element in the unit cell mandate the need for performing spin-polarized calculations? I wanted to find out the DOS, PDOS, and the band structure. I'm new to DFT and I'...
6
votes
0answers
21 views
VASP's NPAR and KPAR for parallelization
What's the best way for parallelization in VASP for periodic systems? In the documentation, it mostly explains it for the local computer and molecule calculation. Apparently, these explanations don't ...
6
votes
0answers
31 views
Inconsistent data of chemical potential from different papers
I am looking for chemical potential from literature:
...
7
votes
2answers
201 views
acceptable range of stretching of a lattice unit cell when we do the heterostructure
Currently, I have to put two different materials together to form a heterostructure. I've already transformed the unit cell of material A from trigonal to cubic. Now the unit cell has a rectangular ...
7
votes
0answers
63 views
How to explain Density Functional Theory results to an experimentalist?
When we present our Density Functional Theory simulation results e.g. lattice parameters, stacking fault energies, band gaps, etc. to people who are experimentalists then the very first question ...
7
votes
2answers
59 views
Combined effects of strain and doping on the electronic structure of semiconductors
I've read papers in DFT studies on band gap tuning in semiconductors and the usually studied methods are either through doping or application of external strain. But it is always just one or the other....
7
votes
1answer
47 views
Different energies for two different geometries where only the monolayer c lattice constant is different?
I carried out a simple single-point PBE calculation on two different graphene monolayers (only c is different) using VASP with 12x12x1 k-grid.
Geometry 1:
...
10
votes
2answers
155 views
Band structure with additive dispersion methods
Let's say I optimized geometry with PBE+D3, does it matter if I make single point bandstructure calculation with just PBE or PBE+D3 since D3 is a additive method.
13
votes
5answers
225 views
DFT software package for a beginner?
I would like to do start doing some basic calculations using DFT. I am interested in solid state physics of strongly correlated materials in 3D (for example high temperature superconductors) or 2D (...
6
votes
0answers
44 views
What are the advantages/disadvantages of QMC over ACFDT-RPA?
I had some experience with the ACFDT-RPA, despite its promising features it's not practical most of the times, and for that reason, I'm looking for a new method for reference calculations. QMC is the ...
10
votes
1answer
154 views
Are QMC calculations practical for periodic structure calculations?
Even some DFT methods or beyond DFT methods such as MP2 calculations are computationally very expensive today even with clusters. If you compare QMC (quantum monte carlo) calculations with them, are ...
11
votes
3answers
171 views
How to determine whether we can put two semiconductor thin film together?
I am beginner of material modelling that's why my question may be basic and I have no direction. If we want to see whether two crystal layer(semiconductor) can be put together, can the DFT calculation ...
9
votes
2answers
36 views
Analytic Hessians for meta-GGA functionals
In many of the free/open-source QM programs like GAMESS, ORCA, NWChem, the calculation of analytic hessians is not possible when a meta-GGA density functional is used, like M06-2X. My first question ...
9
votes
1answer
73 views
Monkhorst-Pack, Gamma-centred and gamma only
Sorry if this question is too simple for this community but I still couldn't find an answer to it.
Do gamma-centred and gamma only grid mean the same thing?
If not, what's the difference?
How do they ...
7
votes
1answer
58 views
What are the methods for calculating interaction energies of layered materials, and where are they implemented?
What are the available methods for the calculation of reference interaction energies of layered materials and in which codes they are implemented? For example, I know RPA-ACFDT in the DFT concept. But ...
8
votes
0answers
30 views
Problem related to the calculation of elastic constant with VASP5.4.4
I am using VASP5.4.4 to calculate the mechanical properties of the cubic phase SnTe. The structure can be found in the materials project website.
In detail, I use the following INCAR to calculate the ...
8
votes
2answers
92 views
Evaluate the orbital magnetic dipole moment within the PAW sphere
In general, the orbital magnetic dipole moment operator is defined as:
$$- {e\over2} \mathbf{r \times v} \tag{1}$$
$\mathbf{v=p}/m$ is true only for simple Hamiltonian like $-1/2\ \nabla^2+V$, but not ...
9
votes
1answer
136 views
Is there a software that has implemented forces of BSE calculations for solids?
I'd like to investigate the structural relaxations of the excited state for periodic systems. It seems BSE is a practical method that has already been implemented in many codes for static calculations....
11
votes
1answer
62 views
adaptive k-mesh
Are there any known codes or scripts to generate an adaptive k-mesh for DFT calculations? For example, I'd like to make the k-mesh near the $\Gamma$ point (e.g., half the zone) more denser ($20\...
13
votes
5answers
2k views
Can I use two different codes?
Can I use one code for geometry optimization and another code for a single point calculation on that optimized geometry? Can one publish results like that?
7
votes
1answer
69 views
Approaches to understanding different relative energies between semiempirical and DFT methods
I am studying Pd(II) metal-organic systems and have used GFN2-xTB (with implicit solvation) for high-throughput optimisation of candidate structures. I use the relative energies (from xtb) of ...
5
votes
1answer
41 views
How to implement scissor-correction in VASP to study optical properties?
It is mentioned here that
It is possible to correct for the DFT band gap error by introducing an empirical scissors correction, which is effectively a rigid shift of the conduction band with respect ...
11
votes
3answers
260 views
External magnetic field in VASP?
I have never found any tags or documentation regarding external magnetic field in VASP but in different well known published articles$^1$, the implementation of the external magnetic field by VASP has ...
8
votes
1answer
83 views
How to perform virtual crystal approximation calculations in VASP?
Can someone share appropriate tags and methods to perform virtual crystal approximation calculations in VASP?
9
votes
1answer
47 views
What is exfoliation energy per unit area?
I see in many sources the exfoliation energy defined with the unit $meV/A^2$ I frankly don't understand how it's calculated and I couldn't find any mathematical formula for that. its unit confuses me. ...
9
votes
1answer
155 views
Can the fermi level of a semiconductor be below the valence band?
I was looking at the data on this page for a NiWO4 calculation.
I can see unoccupied bands near the fermi level that appear to be below the band gap. What does this actually mean physically or is it ...
8
votes
1answer
94 views
How to fix Error Link9999 in Gaussian
I have a problem with geometry optimization in Gaussian software with M062X method. The structure was smoothly optimized using M062X/Gen. Nevertheless, I need very accurate results so afterwards the ...
4
votes
0answers
46 views
What are the some other ways to handle BSSE rather than counterpoise correction and using larger basis sets? [closed]
What one can do to eliminate basis set superposition error (BSSE) if there is no chance to use larger basis sets or counterpoise correction.
12
votes
2answers
336 views
What is Surface termination and how to make surface termination of a crystal structure?
I want to calculate the surface energy of CuO and for that, I've asked CuO (monoclinic) crystallographic plane and their relaxed surface energy. But for the lack of knowledge of the surface ...
11
votes
2answers
174 views
Effect of ISYM tag on Partial Density of States (VASP version < 6)
This is from the entry for LORBIT in the VASP Wiki.
For LORBIT >= 11 and ...
8
votes
0answers
49 views
I ran TDDFT on some small molecules. For some files, the ORCA output files cut short and contain no absorption data. What could be the reason?
Below is just the end of the output file, and the top of the input file. This is for the molecule FDICTF. The calculation did not run out of time. I ran a batch of 15 molecules, all with same ...
10
votes
1answer
381 views
Which method gives the most accurate electron density, and how can it be verified experimentally?
I read a paper from Science (DOI https://doi.org/10.1126/science.aah5975), “Density functional theory is straying from the path toward the exact functional”. They were trying to make a point that ...
7
votes
2answers
59 views
Input constraints while comparing different DFT calculated properties for the same material but different atomic arrangement
Let's consider a fictitious AB type binary alloy. AB is known to exist in a B2 type ordered ...
9
votes
1answer
167 views
How to start with structural defects in monolayer?
First of all, thank you for your help!
You are so helpful every time.
I would like to calculate the influence of the structural defects on the electronic structure in the HfS2 monolayer. With VESTA ...
11
votes
2answers
120 views
Which properties of a material calculated using density functional theory are affected by smearing?
Smearing (smearing width $\sigma$, to be precise) has always been confusing. I understand what it is but can't pin it down when it comes to DFT calculations. Should it be converged like k-points and ...
11
votes
2answers
134 views
Permissible amount of forces on ions in a relaxed structure
An equilibrium structure would be at a local minimum but that doesn't happen with all relaxation calculations. Relaxed structures tend to have some resultant forces on ions. What amount of these ...
8
votes
2answers
86 views
k-points convergence for spin polarised vs non-polarised DFT calculations
Spin-polarised calculations come at a computational cost and I tend to take ISPIN = 2 only after I'm done with a proper initial relaxation of the structure, so the ...
11
votes
1answer
170 views
How would you report the lattice parameters of an alloy, modelled using a supercell
There is a whole lot of literature behind ab initio modelling of alloys with statistical site occupancies. These include VCA, SQS, CPA, supercell approach, etc. This question does not aim to compare ...
17
votes
2answers
908 views
Logic of published geometry optimization results without checking phonons
I see that in many papers where optimization results presented, they do not mention phonons and their force convergence criterion is 0.01 eV/A. Can you publish a result like that? And is not this ...
