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

$\epsilon _{ij}^{\infty }=\delta _{ij}+{\frac {4\pi }{\epsilon _{0}}}{\frac {\partial P_{i}}{\partial {\mathcal {E}}_{j}}},\qquad {i,j=x,y,z}$

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

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

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.

Related Tags and Sections

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

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