calculation of static dielectric constant

[A.Eddiouane]

Dear all,
I've been trying the tree following tests in abinit-7.10.2 version : As results of AlAs tests we have:

1- the input "trf1-5.in" (Response-function of an homogeneous electric field) >>>>>>>>>>>>>>>>>>>>>> the result of dielectric constant is 9.7606048428


2- the input "tnlo-2.in"(BERRY PHASE (field=0 )Compute various quantities from Delta polarization) : >>>Linear optical dielectric constant : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Electronic dielectric tensor = 9.20199931 (9.94846084) >>>Static dielectric constant : >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Relaxed ion dielectric tensor = 10.95641891 (11.84823634)


3- the input ''~abinit/tests/tutorespfn/Input/tffield_6.in'' (Finite electric field calculation of alas at clamped atomic positions) >>>>>>>>>>>>>>>>>>>>>>>>>><>>>>>>>>>>>>\epsilon_11 = 1+ 4 \pi \chi(1)_11= 8.13

please can i know the difference between the dielectric constants generated , and which is the appropriate methode to my calculations given that i aim to find the static optical dielectric constant of BaTiO3 in spontaneous state

best regards

[mverstra]

Most of the dielectric constants are comparable, but will only be similar if you converge everything very scrupulously wrt k-points ecut and maybe bands.

The static dielectric constant adds the phonon contribution to the "infinity" electron-only dielectric constant. This is explained in Kittel or Ashcroft and Mermin, or in Xavier Gonze's double PRB on the method.