the stress in the code is defined as the derivative of the energy per
unit volume with respect to infinitesimal deformations
sigma_alpha,beta = 1/Omega partial E / partial epsilon_alpha,beta
for a deformation such that
r_alpha -> r'_alpha = r_alpha + sum_beta epsilon_alpha,beta r_beta
it is symmetric in alpha,beta because the antisymmetric components of
the deformation (describing rotations) do not change the energy.
If I understand correctly the stress definitions
(https://en.wikipedia.org/wiki/Stress_measures) for infinitesimal
deformations they are all the same
because J=1, F=I, dn_0=dn, ... etc
If you are considering finite deformations the stress is the derivative
taken w.r.t. the present deformed configuration so I think must be the
Cauchy stress because the code does not know you want to take another
configuration as reference.
Therefore, should be something like S = J (F^-1) sigma (F^-1)^T
HTH
stefano
On 17/02/2017 16:27, Mahdi Faghihnasiri wrote:
Dear all,
I know If I set tstress=.true. the stress tensor will be computed and
printed. but What's the kind of the Stress Tensor QE dose print? for example
Cauchy,
true, Kirchhoff, PK2, ...
I am trying to calculate second Piola–Kirchhoff (PK2) stresses with QE. Any
suggestions or comments are appreciated.
Sincerely
Mahdi
*Mahdi FaghihNasiri*
Department of Physics
Shahrood University of Technology
Shahrood,Iran**
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