Questions tagged [density-functional-theory]

For questions about simulations using Density Functional Theory.

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How can I apply symmetry operations to wavefunctions obtained via VASP to map them to the whole BZ from the irreducible wedge?

I have developed a Python tool that extracts the plane wave coefficients and Gvectors from a WAVECAR file and I'm able to get the real space wavefunction for that ...
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2 votes
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study of elastic properties under pressure using VASP

I want to replicate this paper, but somehow I cannot get the same results, most important as shown in table 2. Can anyone help me with this? I have attached the INCAR file. If any correction is needed,...
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4 votes
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VASP DFT+U on Ti d orbital, why d orbitals are not affected but s and p orbitals are pushed lower?

I'm using DFT+U implemented in VASP to calculate the electronic density of states of anatase TiO2. In order to more accurately reproduce the experimental bandgap of anatase TiO2 (as compared to ...
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5 votes
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total force calculated with cp2k not zero

I performed DFT calculations for a box of 64 water molecules under Periodic Boundary Condition using CP2K. I found that the forces on each atom do not sum up to zero, as shown in the attached figure. ...
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How to construct thin film structure of desired thickness in quantum espresso?

I want to study the properties of thin films using DFT calculation. I have done the bulk crystal calculations in Quantum ESPRESSO but have no idea how can I construct the thin film of desired ...
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4 votes
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63 views

Is it possible to obtain the current-voltage characteristic for a crystal using the Hartree–Fock (or DFT) calculation?

In continuation of the question of obtaining an electrical conductivity tensor (ECT) from the “first characteristics”, will my following suggestion be correct? Since a crystal with an applied-to-it ...
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  • 201
4 votes
2 answers
66 views

VASP structure relaxes to an incorrect ground state

I am using VASP to perform a structural relaxation of $\ce{CuNCN}$. I am using the PAW-PBE POTCAR files for the same and the KPOINTS have been generated using a script. The POSCAR file has been ...
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3 votes
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Creating Amber/CHARMM style force field potential for energetic materials using DFT

What are the basic steps and methodologies used in creating inter-atomic force field potential for CHARMM/Amber style for energetic materials with the help of DFT? What are the best possible free ...
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11 votes
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59 views

How to define a chemical bond computationally?

I'm working with an amorphous system. With oxygen, my system has both covalent and ionic bond forming cations. I utilise the Wannier centre approach to define a covalent bond, and my theory is that if ...
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2 votes
1 answer
50 views

How to carry out spin texture calculation( as shown in figure)using VASP?

I could not find any good source for this type of calculation. I'd be very appreciated if someone who is experienced with that to show it step by step
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Can the electrical conductivity tensor of a crystal be obtained from a Hartree-Fock calculation?

Let’s assume that a crystal has been calculated by Hartree–Fock (HF) method (or DFT one), i.d., so to speak, the "first characteristics", which are eigenvalues and eigenvectors, as well as ...
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In which part of the Hartree–Fock algorithm (or DFT one) could a neural network be most effectively used?

I understand that the task of implementing machine learning in DFT and Hartree–Fock (HF) algorithm has already been solved, perhaps to some extent, but it is interesting to think about how to ...
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7 votes
2 answers
289 views

Are dispersion constant calculated differently for elements that are heavier than Xe?

How does one obtain the value of dispersion coefficient $C_6$ for elements that come after Xe. I am going through the original paper [1]. I can see that: $$\tag{1}C^a_6 = 0.05N(I^a \alpha^a),$$ where $...
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4 votes
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14 views

ssr functional for the dft=userd in MRCC package

I found the nice userd example with the standard functional in the latest MRCC manual but I wonder if one can also use ssr (...
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7 votes
3 answers
362 views

Calculate Hessian for configurations that are not at the minimum of the Potential Energy Surface

I want to calculate the Hessian matrix for molecular configurations that are not at the minimum of the Potential Energy Surface, using cp2k. But it seems that cp2k requires the configuration to be ...
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Any software that could convert the format of pseudopotential files?

I am using SIESTA 3.2, which seems to only support the .psf pseudopotential format, is there any tools that allow me to convert the pseudopotential files into another format? Or when generating the ...
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4 votes
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ORCA finished by error termination in SCF gradient

I try to optimize and compute frequencies for the system built up from C, O, H, and Co atoms in the following functionals: B2PLYP, B2PLYP-D3, B3LYP, B3LYP-D3, BLYP, BLYP-D3, DSD-PBEP86, PBE, PBE-D3, ...
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33 views

Optimization converged but frequency calculation does not

I tried a three-step job file for gaussian. This is my input file: ...
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68 views

Is it possible to build a force field that suits all elements based on vasp's machine learning result?

I have tried to use VASP's machine learning force field calculation during running molecular dynamics simulation with a supercell including some elements of Ti, O, Cu, etc. It does increase the speed ...
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7 votes
1 answer
41 views

Is the HOMO energy obtained from GW calculation always a value relative to the vacuum energy (-Ip)?

Aim: I want to obtain a reasonably accurate ionization energy (or work function in other terms) for a 2-dimensional hBN monolayer. The exact material does not matter much respective to the question, ...
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3 votes
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42 views

Coulomb energy in VASP

In DFT, the Coulomb energy is defined as the sum of Hartree energy, nuclear-electron attraction, and nuclear-nuclear repulsion. In VASP output, we can find the Hartree energy, and also the nuclear-...
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6 votes
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72 views

Is there a system of multiple interacting quantum particles for which density can be obtained analytically?

I know that it is impossible for real electrons and nuclei. In the Kohn and Sham approach, a system of interacting electrons is approximated by a system of non-interacting Kohn-Sham particles in an ...
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4 votes
2 answers
536 views

Which formalism is better suited to model a crystal with defects: Hartree–Fock, Kohn–Sham, or something else?

Let’s suppose that (1) it’s required to calculate a crystal with certain parameters of a crystal lattice; (2) this crystal has some defects (let it be Frenkel defects for simplicity); (3) these ...
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3 votes
1 answer
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What does it mean if the Fermi level crosses into the valence band? How about into the conduction band?

Just recently got into DFT and I've been doing a few calculations on my own on Quantum Espresso. I've come up with electronic band structures for materials that I've been looking at and I was hoping ...
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7 votes
0 answers
90 views

What is the best cell shape to calculate the energy of a free atom with a periodic DFT code (VASP)?

I want to study the adsorption energies of many different atoms to some surfaces. For that, I need to calculate the energies of free atoms (adsorbates) in a vacuum. I understand that I am supposed to ...
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6 votes
1 answer
181 views

Raman Spectra in Quantum Espresso

Does anyone have any experience simulating Raman spectra in Quantum ESPRESSO? Following the example 15 that comes with QE, I have attempted to simulate the Raman spectrum of MgO. I know the lraman ...
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1 answer
110 views

Future and limitations of DFT

I'm a graduate student beginning research in condensed matter physics. Naturally, I am very interested in mathematics. I am aware that, in condensed matter physics, theorists employ tools from pure ...
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5 votes
1 answer
73 views

Successfully running parallel gas phase calculation on AMD cloud instance but implicit solvent fails (Local Intel workstation successfully runs both)

I am using an AMD Linux cloud-based instance to ran general optimisation and transition state calculations in parallel. I have noticed that I can run gas phase calculations in parallel but the run ...
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8 votes
4 answers
1k views

DFT code for simulating thousands of atoms in a supercell

I'm trying to simulate a supercell that contains thousands of atoms with the DFT method, but it seems VASP couldn't handle such a large system, its parallel efficiency is relatively low, when I try to ...
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  • 1,601
6 votes
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53 views

density of state with spin orbit coupling

I have been doing DOS calculations with SOC tag on in VASP, and another calculation without SOC. As shown in the figure the DOS with SOC seems strange! is this wrong? How can I have resolved I have ...
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how to simulate the size effect with DFT theory?

I am considering simulating the size effect of nanoparticles, the size expands from 0.2nm to 50nm, but when trying to build the model, I am not sure how to reflect the size correctly, for example, if ...
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4 votes
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27 views

Predicting the band gap or some other properties of materials before running any calculations

Can we some how predict what sort of modulation will doping do to a material without actually running any calculations. Like perhaps we use the already known DOS of Zn in order to predict whether the ...
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8 votes
1 answer
246 views

Transiesta output through a single gold atom

I am looking for the electron transport study in a single gold atom, like the system of single carbon atom shown in transiesta paper by Nick Papior et al. Computer Physics Communications, 212, 8-24, (...
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4 votes
0 answers
31 views

How to save the generated 3d representation of the structure(s) by Viewer3d in Py4vasp?

I used py4vasp to calculate structure from data and then I displayed them in a structure viewer (Viewer3d) by this line: calc.structure[:].plot(). It returns a ...
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6 votes
1 answer
469 views

How to do simulation when two atoms exist in the same coordinate position in the lattice?

I found that there is a type of substance in which two atoms exist in the same coordinate position in the lattice, for example, FeF3(H2O)3, here is its crystal ...
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  • 1,601
6 votes
1 answer
233 views

Effective mass of holes was measured using DFT

Effective mass of holes was measured using DFT. The hole value is different for each band, is there a way to get the average or standard value of this value? It was calculated using the VASP program. ...
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6 votes
1 answer
244 views

Why can't DFT calculate the accurate electronic configuration of the Oxygen atom?

I am trying to do a DFT calculation of Oxygen atoms with the VASP code. My settings follow the official tutorial on the Oxygen atom of VASP. But it turns out the energy levels of the two spin ...
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4 votes
0 answers
65 views

Why can't DFT calculate the energy of magnetic diatomic molecules accurately?

I am trying to calculate the reaction enthalpy change of $\ce{2H2 + O2->2H2O}$, my plan is to calculate the energy of $\ce{H2, O2 \text{and} H2O}$, respectively, then do the simple math. But I find ...
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3 votes
0 answers
22 views

How to estimate Photocurrent or Photo electron emission probability through Quantum espresso?

Or is there any Analytical methods available to estimate material response to incoming photon radiation.
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7 votes
1 answer
109 views

When is coupled cluster preferred over DFT?

I know that coupled cluster is considered to provide better accuracy than DFT, but I am not sure for which materials science applications or types of molecules that this higher accuracy is considered ...
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5 votes
1 answer
159 views

Simulating autoionization of small molecules using DFT or AIMD

From what I’m reading, simulation of autoionization in liquid substances is hard to do using gas phase DFT or AIMD[1][2][3]. I am using ORCA to do my work and I must confess that I’m shocked to see ...
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7 votes
0 answers
98 views

Scaling and speedup of Real-space based DFT calculations using Finite Elements approach

I have recently encountered paper where the authors have formulated Kohn-Sham equations using the finite-element package deal.II. It stated in paper DFT-FE was significantly faster than QE for all ...
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6 votes
1 answer
84 views

Are there any available tools to implement Jellium models?

I want to solve a Jellium-DFT like problem. Does any of the self-consistent/DFT software packages available allow to solve for the case of a Jellium configuration (no lattice)? If not I would like to ...
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  • 213
14 votes
2 answers
232 views

Textbooks for electronic structure theory

Through this post I am looking to create a resourceful list of textbooks for any one interested in electronic structure theory. The focus here is to create mostly a mutually exclusive list of answers ...
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7 votes
1 answer
104 views

Analytic gradient and hessian for B3LYP

I'm studing DFT and I would like to know if there is an analytic expression for the first and second order derivatives of the PES obtained through the functional B3LYP. If so, I would need some ...
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3 votes
0 answers
29 views

Can you Calculate Magnetism at a Material's Surface?

I'm doing some research on FePt L10 nanoparticles, and I'd like to know how their surfaces affect their magnetic properties. However, I can't seem to find any papers on this topic. Specifically, I ...
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4 votes
1 answer
104 views

Decide the position of oxygen vacancy via the configuration with the lowest energy?

I am trying to determine the position of oxygen vacancy in $\ce{TiO2}$, is it reasonable to decide it by choosing the configuration with the lowest energy? It doesn't feel quite right to always choose ...
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  • 1,601
2 votes
0 answers
75 views

Rashba effect and VASP

How to prove by first-principles DFT calculations that the compound has Strong spin-orbit coupling and Rashba effect
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  • 495
1 vote
0 answers
37 views

Exchange potential for a non-interacting system

If I have a system of two "non-interacting electrons" and I want to mimic its density using another non-interacting system (KS system). Would the KS potential contain the exchange potential?
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3 votes
0 answers
71 views

band structure and primitive cell

When I use VASPKIT tool or SeeK-path to generate K-path file for a band structure calculation, it gives a PRIMCELL.vasp file , which has a unit cell that is ...
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