[Pw_forum] Kind of Stress tensor
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 ___ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
Re: [Pw_forum] Kind of Stress tensor
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** ___ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum ___ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
[Pw_forum] Silicon DOS issue
Dear community, I am unable to obtain the square root energy dependency of the bulk Silicon conduction band DOS, despite using a fine k grid (100x100x100). I expect the DOS near conduction band edge (below the second conduction band of silicon) has a square root dependence with energy. I plotted out the (DOS)^2 vs energy I obtained here: http://imgur.com/a/Wu07z As you can see, (DOS)^2 vs. energy is not linear, meaning DOS is not having a square root dependence with energy. Is this an known problem or am I doing something wrong? Here is the nscf calculation input deck: --- &control prefix='silicon', pseudo_dir='../pseudo/' outdir = './results', tstress=.false., tprnfor=.false., calculation = 'nscf', verbosity='high', / &system ibrav= 2, celldm(1) =10.2623466921, nat= 2, ntyp= 1, ecutwfc = 30.0, ecutrho=300.0, input_dft='PBE', nbnd = 8, / &electrons diagonalization = 'david', conv_thr = 1d-08, mixing_mode = 'plain', mixing_beta = 0.7, / ATOMIC_SPECIES Si 28.086 Si.pbe-n-rrkjus_psl.0.1.UPF ATOMIC_POSITIONS Si 0.00 0.00 0.00 Si 0.25 0.25 0.25 K_POINTS automatic 100 100 100 0 0 0 --- Thanks! Xufeng ___ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
