My Community

I try to repeat the calculation of fluorine displacement dipole (Born effective charge) in NaF from the manual.
In the final step,

delta <R> = delta <R>ion + delta<R>el = ( -3.33E-05 -3.33E-05 -0.0429)

and we move the F atom along z direction

undist ---- (0 0 0),(0.5 0.5 0.5) dist ----(0 0 0),(0.51 0.51 0.49)

Hence, we move the F-sublattice by = 0.045102 electron/A.
then we get the Born effective charge for flurine in NaF

Z* --> (-0.000739 0.000739 -0.951177)

but in the manual , it show only Z* = -0.9740.
What is wrong ?
Z* must be a tensor ?

in the discussed example (cubic NaF, displacement of F in the z-direction only) , the effective charge tensor reduces to a scalar due to symmetry reasons.
please check if the x and y components of the Berry phase term are due to spurious contributions.

As a clarification, in all cases the statements made are that the F atom is displaced in the cartesian Z-direction only, and yet we have the following:

Equilibrium:
0.5000 0.5000 0.5000

Displaced:
0.5100 0.5100 0.4900

The displacement is obviously in all 3 directions, simultaneously. Also, when I run the calculations in sec. 6.59 of the manual "Berry phase calculation", I consistently fail to obtain the quoted results.

Is there perhaps a misprint in the manual, or is there some hidden detail that I have so far failed to notice?

The positions are given in direct coordinates leading to:

Start configuration:
0.5*(0, 0.5, 0.5) + 0.5*(0.5, 0, 0.5) + 0.5*(0.5, 0.5, 0) = (0.5, 0.5, 0.5)

Displaced:
0.51*(0, 0.5, 0.5) + 0.51*(0.5, 0, 0.5) + 0.49*(0.5, 0.5, 0) = (0.5, 0.5, 1.02*0.5)

so there should just be a displacement in the z-direction.

Best regards,
/Dan