Questions tagged [vasp]

For questions about use of the Vienna Ab initio Simulation Package (VASP).

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5
votes
0answers
32 views

What is the difference between Ultrasoft , ONCV and PAW Pseudopotentials? Which is better for a spin-orbit coupled calculation?

I am trying to do spin-orbit coupled calculations for various topological insulators. I have found papers using Quantum Espresso with ONCV pseudopotentials and papers using VASP with PAW ...
7
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1answer
116 views

Is it okay to take a cubic Monkhorst-Pack k-mesh for a non-cubic supercell in a DFT calculation?

Assume that the numbers of k-points in each direction are sufficient. Example - Lengths of lattice vectors: $2\: 2\: 4$ Required k-mesh: $9\times 9\times 5$ Would a $9\times 9\times 9$ k-mesh work? ...
8
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1answer
87 views

Moving from VASP to CASTEP for bulk crystal and surface calculations

Can someone that works with CASTEP and VASP explain to me how a workflow might change between the two programs? I am very familiar with VASP but have not used CASTEP before. As an example, assuming ...
11
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2answers
361 views

k-points and ENCUT convergence tests before or after relaxation?

Let's say I want to relax a structure using VASP. K-points and ENCUT convergence tests must be conducted before or after relaxation? and which tags should be ...
12
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4answers
213 views

How to make a k-point convergence test for a bulk structure with a lower k-point in the z-direction?

Let's say I want to make k-point convergence test for graphite. And let's say it converges at 12x12x4. Do I first need to do a k-point convergence test for equal k-points on xyz directions then make ...
8
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1answer
71 views

What resources are available to learn how to do something in VASP?

Apart from what is obvious (from a Google Search), what are the various resources available if I want to learn how to do something in VASP (for example, starting an HSE06 calculation)?
7
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1answer
110 views

Why is VASP so popular for 2D materials?

I have seen that in many articles of 2D materials calculations that VASP is the most used one among DFT codes. Could please explain to me why?
4
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1answer
25 views

How to create a POSCAR for hexagonal structure for VASP calculations?

The method that I am following in creating a hexagonal lattice POSCAR file is by downloading it from https://materialsproject.org/ website. Now, I want to learn how to create it manually starting from ...
6
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1answer
61 views

How to extract lattice constants a and c from relaxed hexagonal structure using VASP?

Taking a bulk WS$_2$ (bilayer) structure and relaxing it with ISIF=3 and IVDW=10 (DFT-D2 method) using the VASP code. Then ...
5
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1answer
48 views

Best vdW correction functional for transition metal dichalcogenides

For relaxation of transition metal dichalcogenides (e.g.: WS2) using the VASP code, what is the best choice for vdW correction method (e.g.: DFT-D2, DFT-D3 or optB88-vdW) that can give you good ...
10
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1answer
76 views

Simulated low energy electron diffraction (LEED) patterns

BOUNTY GRACE PERIOD: Ending in 24 hours! Any answer today will be eligible! What modern software supports the generation of LEED patterns? It seems most LEED simulation packages are quite old and do ...
6
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1answer
25 views

Work Function Problem

2D materials (such as graphene) are mostly exfoliated from their 3D bulk counterpart. I am wondering how we can calculate work function for a 2D material? Normally electrostatic potential in the out-...
9
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1answer
46 views

Edge states in Topological Semimetals

Does it make any sense to calculate edge states for topological semimetals while they don't have any global gap?
10
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1answer
47 views

Spin density in systems with non-collinear magnetism using VASP

I have recently been working with non-collinear antiferromagnetic systems. I understand that, in order to obtain spin density, one must obtain the electron density in one configuration of spin and ...
8
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1answer
40 views

Electric Field Calculations in VASP

Can someone share appropriate tags and method to apply Electric Field in VASP?
9
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1answer
49 views

Phonon Calculations for Bilayer 2D systems

I am facing problems in calculating the phonon band structure for bilayer 2D systems. While the band structure mostly shows positive frequencies for the 1 layer system, going to 2 layers makes some ...
14
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1answer
138 views

Standard values for level of convergence

In matter modelling we use self consistent approaches for calculating different properties. Many DFT codes find the ground state of the system by determining total energy self consistently. Going ...
11
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1answer
99 views

Dealing with symmetry of ordered primitive cell during DFT structure relaxation

I have a large disordered cubic structure that I would like to do AIMD on to look at cation diffusion. I found the primitive cell and then ordered it to create several configurations. I will then ...
13
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2answers
99 views

Quantum Dot properties using VASP

We are working on the excitonic properties of cadmium-based Quantum Dots (QD) and QD heterostructures. We have MedeA-VASP and hence we managed to make QD structure. Are QD calculations different from ...
7
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1answer
50 views

VASP vs MedeA-VASP

MedeA® is a software package developed by Materials Design Inc for atomistic simulation of materials. According to official website VASP can only be acquired legally by either purchasing a license ...
11
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1answer
84 views

Real space projection vs reciprocal space projection in DFT calculations

When doing VASP calculations for large cells, we get a warning: "You have a (more or less) 'large supercell' and for larger cells it might be more efficient to use real space projection ...
16
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1answer
125 views

Difference between potential energy, free energy and Coulomb energy in solid state physics

I often encounter terms such as (Helmholtz, Gibbs) free energy, potential energy and total energy when describing the energy of a physical system at atomic level. Sometimes I stumble upon Coulomb ...
14
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1answer
182 views

Ab initio molecular dynamics to check material stability at finite temperature

I completed an ab initio molecular dynamic (AIMD) simulation in VASP for a hypothetical material. The simulation was done for 5ps with 1fs steps and the temperature was set to 300K using Nosé–Hoover ...
18
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2answers
191 views

Semi-infinite surfaces for adsorption: a valid approach?

I'm currently trying to surface reaction of small molecules on metal oxides in VASP. Several papers I've read have approached surface energy calculations in a variety of ways. I first began looking at ...
14
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1answer
136 views

How to convert from primitive to conventional after structure relaxation?

I did this in VASP but I guess this would be the case for any program. I have a structure that has a cubic conventional cell (a = 9.86 A). I found the primitive cell (a=b=c=6.97, alpha=90, beta=60, ...
12
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0answers
84 views

Correlation Functions in the Cluster Variation Method [closed]

I've been referring to Dr Mohri's paper [DOI: 10.1007/s11837-013-0738-5] for the cluster variation method (CVM). I wish to calculate the configurational entropy of a binary FCC system. Cluster ...
14
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1answer
226 views

Why is the band gap of graphene “opened” in this VASP calculation?

I used VASP to do the band structure calculation on Graphene. Originally I would expect that the Dirac cone can be observed in the K point. If we watched qualitatively, we can see this behavior. But ...
18
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2answers
121 views

Calculating binding energy between two systems

Regarding the calculation of binding energy of molecular absorption on graphene, for which this has been discussed before, the process of calculating $E_{AB}$ is fairly straight forward, i.e., it is ...
14
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1answer
115 views

What are the ways to ensure thermodynamic stability of a DFT modelled new structure?

One way of predicting the thermodynamic stability of a DFT modelled structure is to calculate the energy above convex hull, which was used as the criterion in The Materials Project database. For ...
11
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3answers
221 views

How to analyze the space group of a relaxed structure that has fractional site occupancies

I am using VASP package to model a material that has fractional site occupancies. An appropriate supercell (cif) was generated using supercell package and converted ...
12
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1answer
75 views

DFT vs tight-binding solutions for a Dirac cone in graphene: Why is the DFT version squeezed?

I'm a beginner at DFT calculations with VASP software. I use it to calculate the band structure of graphene and I obtain the following result: I used it to calculate the band structure of graphene ...
15
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1answer
105 views

VASP Dielectric constants: What potential to use?

I've simulated the dielectric constants using the LEPSILON = .TRUE. tag and the PBE GPAW potentials. A collegue mentioned that for accurate results norm conserving pseudo-potentials are the way to go. ...
19
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3answers
165 views

Hexagonal lattice volume EOS fit

I have a little problem concerning hexagonal volume fitting using VASP. I have followed these steps: Relax the structure from a given volume using ISIF =4 Copy ...
8
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1answer
48 views

VASP output energy

Which VASP output energy, after sigma -> 0 or before, do you use when combining with zero point energy and vibrational entropy obtained via vtst tools? (Vtst tools provide the vibrational frequencies ...
8
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1answer
147 views

Is LDA better than GGA for elastic constants?

I have calculated elastic constants for Si, GaAs, and GaN using LDA and GGA in VASP. LDA is giving better results than GGA for elastic constants. Is there is a reason behind the good results by ...
17
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1answer
182 views

How does the mBJ potential give an accurate band gap as compared to LDA and GGA?

I am not able to understand the literature on how the modified Becke-Johnson(MBJ)$^{[1]}$ potential gives an accurate bandgap. Can someone please help? Thank you. The formula for the potential can be ...
16
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1answer
75 views

How to ensure a smooth band structure?

I performed an HSE06 calculations using VASP and the calculated band gap is in good agreement with experiment. However the band is not smooth, with very sharp, zig-zag like features. How to improve ...
19
votes
4answers
190 views

What is the status of graphics processing units in plane-wave DFT?

A few years back, I performed a few calculations of metallic slabs using VASP and the Atomic Simulation Environment (ASE). I'm by no means an expert, but I noticed that the calculations were very CPU ...
21
votes
2answers
264 views

Quantum ESPRESSO vs VASP

We know that both Quantum ESPRESSO and VASP can perform lots of different kinds of simulations of materials. But what can VASP do that Quantum ESPRESSO can not, and vice-versa?
11
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1answer
50 views

Why is the Nonequilibrium Green’s function (NEGF) method for quantum transport not implemented in plane wave codes like VASP and Quantum Espresso?

DFT codes like Siesta, QuantumATK, Questaal, and Smeagol having localized basis sets have NEGF implementations available. But not in plane wave codes like VASP and Quantum Espresso. Why is it so?
17
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1answer
161 views

Are there problems with the Tran-Blaha modified Becke-Johnson potential (mBJ, a.k.a. TB09) in Quantum ESPRESSO?

I have used the modified Becke-Johnson (mBJ) exchange potential before, as it was developed and implemented in Wien2K by Fabien Tran and Peter Blaha (1). In 2013, Éric Germaneau et al. implemented mBJ ...
12
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1answer
72 views

What are the pre/post processing tools available for VASP?

I am aware of pyPROCAR and VASPKIT. Are there any other tools supporting VASP
10
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1answer
67 views

Hexagonal lattice optimization

I have downloaded POSCAR file for "WS2" from "materials project website". I want to do lattice optimization, draw "Energy versus lattice parameters" curves, and calculate Bulk modulus through Birch–...
22
votes
1answer
118 views

What are good ways to reduce computing time when working with large systems in VASP?

I know that parallelization is an important factor, however, I wanted to know if there are any other methods of reducing computing time when dealing with large systems without sacrificing accuracy. ...
16
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1answer
92 views

In VASP, how is the chemical potential of elements calculated?

I would like to calculate the chemical potential of elements having different environmental condition (rich or poor) using VASP. How is this accomplished?