QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: debashishdashnits on April 5, 2017, 16:17

Title: Wrong result as per theoretical formula
Post by: debashishdashnits on April 5, 2017, 16:17

Hello to all,

I am working on Cubical material and trying to find out elastic constants . As per formula available in different papers, I correctly found bulk and shear moduli which also matches with simulation results. But Young's modulus, I am getting wrong. As per theory, the formula is (Y=9BG/G+3B). When I am putting data's in this, getting wrong results. Any one knows any other formula or Whether quantumwise uses some other formula???

Title: Re: Wrong result as per theoretical formula
Post by: Petr Khomyakov on April 5, 2017, 22:21

I am not sure I have understood your question. Have you calculated the elasticity tensor (elastic constants) in ATK? Do the obtained elastic constants agree with experiment?

Title: Re: Wrong result as per theoretical formula
Post by: Julian Schneider on April 6, 2017, 09:27

VNL calculates the Young's modulus as Y_i = 1/S_ii  (i=x,y,z) where S is the inverse of the elastic constants matrix.
We do not calculate the bulk modulus and the shear modulus directly, but from the elastic constants, as well. Since there are several conventions how to do this exactly (Hill, Voigt, Reuss) which all use slightly different formulas, it is more straightforward to calculate the Young's modulus from the elastic compliance matrix, since that does not rely on any of these conventions.