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 ...
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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. ...
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  • 3,269
5 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 ...
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  • 327
4 votes
Accepted

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-...
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  • 3,269
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, ...
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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 ...
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  • 601
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(...
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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 ...
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  • 3,269

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