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7 votes

Exploring Elastic Constants Calculation in VASP: Methods and Best Practices

Theoretical Background: Elastic constants can be calcualted in one of two approaches. First is via the stress-strain relationship, and the second is by strain-energy relationship. First approach: In ...
Jaafar Mehrez's user avatar
7 votes

How to use the ev.x tool in Quantum ESPRESSO?

This answer is partly based on the Computational Materials Physics Course by Stefaan Cottenier. Follow the steps provided below: Prepare a text file with two columns, the first column being the unit ...
Mohamed's user avatar
  • 695
6 votes
Accepted

Elastic property in Voigt, Reuss and Hill approximations

Voigt and Reuss bounds are considered as limits within which the polycrystalline elastic modulus can exist. Many other bounds have been proposed subsequently to bridge the gap between theoretical ...
Pranav kumar's user avatar
  • 4,278
6 votes

How can we make a mechanically unstable cubic system, stable

Depending on your calculation and how much time you want to invest in getting the best property you can, I suggest two different approaches to make this system stable: Fully relax the geometry of the ...
Brandon Bocklund's user avatar
5 votes

Elastic constants calculation

The Elastic constants are calculated within vasp using IBRION=6 and ISIF=3. The Elastic constants are calculated from stress-strain relationship by applying finite distortion of lattice and ions. ...
Pranav kumar's user avatar
  • 4,278
4 votes

elastic constants transformation/basis change P21/a -> P21/n

In order to define the matrix transforming the P21/n structure into P21/a it is imperative to know the unique axis of both space groups. For example the contracted P21/n symbol can be used for the ...
gryphys's user avatar
  • 661
4 votes
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Elastic properties of graphene by using DFT (Quantum espresso)

The elastic stiffness $C_{j}$ with respect to each $j$ direction mediates the energy $E$ at a deformed structure and the mechanical strain $\epsilon_{j}$ as follows [Mir, S. H. et al. ACS Omega. 2020, ...
Patche's user avatar
  • 400
4 votes

How can I calculate the elastic properties of a unit cell and a supercell?

There is new tool called ElasTool. It is a Python-based toolkit for computing the second-order elastic constants (SOECs) and mechanical properties of crystal systems. It is designed to integrate with ...
Thomas's user avatar
  • 9,142
4 votes

Fitting of Brich-Murnaghan equation of state

If you know Julia, I have a package called EquationsOfStateOfSolids.jl that is designed to do this. It currently can fit and evaluate $E(V)$, $P(V)$, and $B(V)$ on several equations of state: ...
Ryan's user avatar
  • 176
4 votes
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How to start with the elastic properties of 2D materials using the VASP code?

Elastic constants can be derived from constitutive relationship by calculating stresses from a strained system $$\sigma_{ij}=C_{ijkl}\epsilon_{kl}$$ Once the crystal is deformed by some finite strain ...
Pranav kumar's user avatar
  • 4,278
4 votes
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What is the difference between elastic and mechanical properties of materials?

When we talk about mechanical properties, we generally refer to response of the material on application of external load. Apart from external load, responses can be of mixed nature, such as thermo-...
Pranav kumar's user avatar
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4 votes

How to do a proper relaxation of the multicomponent structure?

A few things: If you start with your supercell of pure bcc Ti, the spacegroup symmetry will be Im-3m, as expected. As soon as you replace one or a few atoms of Ti with Nb, or any different species, ...
Brandon Bocklund's user avatar
3 votes

Elastic constant calculation

The deformation parameter ($q$) in your strain matrix ($q$=0.0015) seems to be 10 times smaller than the increment ($q$=0.015) in the lattice-vector matrix. To correct for this, you can fit to $E=a+b(...
Raghunathan Ramakrishnan's user avatar
3 votes

Why VASP calculates the elastic constant for another trigonal space group?

Elastic constants can be calculated using two approach, one with Energy-strain relationship and another with stress-strain relationship. The key ingredient in above two methods is energy or stress at ...
Pranav kumar's user avatar
  • 4,278
3 votes

Fitting of Brich-Murnaghan equation of state

Here are some references from my own work: a script that reads energy-volume data from a csv file and fits a Vinet equation of state: https://github.com/flokno/tools.mlff/blob/main/mlfftools/scripts/...
flokno's user avatar
  • 136
3 votes

What is a good material to use in a blood vessel model?

What an interesting question! You are definitely creating a model... unfortunately 'modelling' in the context of this site means 'computer modelling'. See here for an explanation of what this site is ...
Tyler Sterling's user avatar
2 votes

Assessing Accuracy of Elastic Constants for 2D Materials Calculated via VASP and VASPKIT

Symmetries The elastic constants tensor obtained should reflect the symmetries of the crystal structure of the material in question. This comment article can be a helpful reference. Elastic constants ...
CW Tan's user avatar
  • 1,316
2 votes

How can I calculate the in-plane stiffness and Poisson’s ratio of a graphene monolayer?

If you already have the elastic constants $C_{ij}$ (in Voigt notation), you should be able to use the following equations for the general angle-dependent in-plane Young's modulus $E(\theta)$ and ...
CW Tan's user avatar
  • 1,316
2 votes

How to calculate 2D elastic constants of boron nitride monolayers from uniaxial strains?

I think you should take a rectangular unit cell instead of the hexagonal unit cell depending on this article (The response of mechanical and electronic properties of graphene to the elastic strain M. ...
2 votes

How to compute the Elastic Modulus of a molecule using GROMACS?

You can apply certain strains to the system by modifying the input structure, e.g. stretching one direction and fixing the other directions. After running MD, one can extract stress components. Keep ...
Lukas's user avatar
  • 303
1 vote

Supercell Elastic Constant

In the undoped case, when considering a cubic crystal structure and using a tetragonal supercell not changes point symmetry, Hence number of independent elastic constants remains three. If you rotate ...
Pranav kumar's user avatar
  • 4,278

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