Questions tagged [density-functional-theory]

For questions about simulations using Density Functional Theory.

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9
votes
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
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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
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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
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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
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0answers
31 views

Inconsistent data of chemical potential from different papers

I am looking for chemical potential from literature: ...
7
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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
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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
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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
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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
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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 ...

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