Should the volume of a material change with the application of uniaxial or biaxial strain?

Payal Wadhwa @Payal_Wadhwa

07 July 2018 4 6K Report

Suppose, I have an FCC system having POSCAR as follows

YSb

6.2000000000000002

-0.0000000000 0.5003829369336542 0.5003829369336542

0.5003829369336542 -0.000000000 0.5003829369336542

0.5003829369336542 0.5003829369336542 0.00000000000

Y Sb

1 1

Direct

0.00000000000 0.0000000000000000 0.0000000000000000

0.5000000000000 0.5000000000000000 0.5000000000000000

Then i applied 1% uniaxial strain in z-direction on it with POSCAR as follows

YSb

6.2000000000000002

-0.0000000000000000 0.5003829369336542 0.505386766

0.5003829369336542 -0.0000000000000000 0.505386766

0.5003829369336542 0.5003829369336542 0.000000000000

Y Sb

1 1

Direct

0.0000000000000000 0.0000000000000000 0.00000000000000

0.5000000000000000 0.5000000000000000 0.50000000000000

Firstly, is it the correct way to put uniaxial strain?

Secondly, it is clear that volume of the system will change. But, in experiments, elongation in one direction will compress the other directions, makes the volume constant.

Then, what is the problem with strained POSCAR? Should volume of the material change with strain?

Kindly help me for the same.

Thanks in advance!

A. M. Lomonosov

Uniaxial or biaxial strain does change the volume of a solid so that V=V0*(1+exx+eyy), where exx and eyy are strains. Or did you mean uni- biaxial stresses?

If you apply an uniaxial stress, say you stretch the rod in one direction, its cross-section decreases. That transversal strain depends on the Poisson's ratio. In solids it is less than 1/2 and the volume increases. In fluids Poisson's ratio = 1/2 and the volume remains the same.

There are some exotic materials with negative Poisson's ratio which volume will decrease under tensile uniaxial load, but normally it grows.

Payal Wadhwa

Dear A.M. Lomonosov,

Thank you for the kind response.

One more thing i wanted to ask is it the correct way in which i have applied strain on a primitive unit cell of FCC? For uniaxial, should we consider one axis say x- or y or z, or we have to consider a1 or a2 or a3 which consists of x, y as well z. Which one is the correct way to apply strain?

Kindly suggest me the same.

Naga Venkateswara Rao Nulakani

Hi Payal

you can apply uniaxial tensail strain along z-axis (alongate the z-axis than the equilibrium value), and try to optimize the cell only along x and y-directions with out changing your z-vector. So, your x- and y-vectors will compress....................(1)

In the same way, optimize the x- and y-axis with compressed z-vector than the equilibrium vector, that will alongate your x- and y- vectors......................(2)

I think this solves your problem

With best regards

Venkat

Thank you Venkat. But which ISIF flag should we use to optimize the cell along x and y-directions with out changing the z-vector?

Thanks again!

How to perform band structure calculations with HSE + SOC in VASP?

How can we make POSCAR of crystalline disordered material Ge2Sb2Te5?

How can we determine the weak topological phase in 3D topological insulator?

How should we choose the no. of filled bands to calculate the parity of topological semi-metals?

Should symmetry operations get changed with the inclusion of SOC?

Can band gap increases with the increase in width in graphene nanoribbons with defects?

What is the physical meaning of Charge conjugation symmetry operator C = +1 or -1 ?

What are High symmetry points in a crystal?

How can we correlate melting point, dielectric constant and Young's modulus of a material with its band gap?

What is the approximate time for GW calculations in VASP?

Why are the velocities so high in my Boussinesq approximation Fluent simulation?

What is the characteristic length to determine the Reynolds number for the scattered turbulent fluid flow?

Can we distinguish the type of free fluid inside the pelvic and abdominal cavities whether blood or serous fluid using the ultrasound?

How much pressure we can reduce at the outlet to avoid Reverse Flow?

How to show arrows over the streamlines in CFD-post?

Timeout error!! Processor in the loop (PIL) using STM32F4 Matlab 2018a?

How to increase mesh quality of a cfd model in ansys fluent?

Is anyone familiar with the cyclic compressive fatigue testing (BS EN 12697 - 25) ?

Is there a deep reason for using the squared modulus of the wave function as the probability density of the existence of the particle?

No title