LCALCEPS

LCALCEPS = .TRUE. | .FALSE.
Default: LCALCEPS = .FALSE. 

Description: for LCALCEPS=.TRUE. the macroscopic ion-clamped static dielectric tensor, Born effective charge tensors, and the ion-clamped piezoelectric tensor of the system are determined from the response to finite electric fields.

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For LCALCEPS=.TRUE., VASP calculates the ion-clamped static dielectric tensor

$\epsilon^\infty_{ij}=\delta_{ij}+ \frac{4\pi}{\epsilon_0}\frac{\partial P_i}{\partial \mathcal{E}_j}, \qquad {i,j=x,y,z}$

the Born effective charge tensors

$Z^*_{ij}=\frac{\Omega}{e}\frac{\partial P_i}{\partial u_j} =\frac{1}{e}\frac{\partial F_i}{\partial \mathcal{E}_j}, \qquad {i,j=x,y,z}$

and the ion-clamped piezoelectric tensor of the system

$e^{(0)}_{ij}=-\frac{\partial \sigma_i}{\partial \mathcal{E}_j}, \qquad {i=xx, yy, zz, xy, yz, zx}\quad{j=x,y,z}$

from the self-consistent response to a finite electric field ε. In this case, the "response" of the system is the change in the polarization P, the Hellmann-Feynman forces F, and the stress tensor σ.

To this end VASP will perform essentially three successive calculations, with:

EFIELD_PEAD= εx 0 0

EFIELD_PEAD= 0 εy 0

EFIELD_PEAD= 0 0 εz 

where, by default, VASP chooses ε_x=ε_y=ε_z=0.01 eV/Å.

This default may be overwritten by specifying

EFIELD_PEAD= εx εy εz

in the INCAR file.

Related Tags and Sections

LEPSILON, LCALCPOL, EFIELD_PEAD, LPEAD, IPEAD, LBERRY, IGPAR, NPPSTR, DIPOL, Berry phases and finite electric fields

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