LCALCEPS: Difference between revisions
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from the [[Berry_phases_and_finite_electric_fields#Self-consistent_response_to_finite_electric_fields|self-consistent response to a finite electric field]] <span style="font-size:16pt">''ε''</span>. | from the [[Berry_phases_and_finite_electric_fields#Self-consistent_response_to_finite_electric_fields|self-consistent response to a finite electric field]] <span style="font-size:16pt">''ε''</span>. | ||
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. | 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: | |||
{{TAG|EFIELD_PEAD}}= <span style="font-size:16pt">''ε''</span><sub>x</sub> 0 0 | |||
{{TAG|EFIELD_PEAD}}= 0 <span style="font-size:16pt">''ε''</span><sub>y</sub> 0 | |||
{{TAG|EFIELD_PEAD}}= 0 0 <span style="font-size:16pt">''ε''</span><sub>z</sub> | |||
where, by default, VASP chooses <span style="font-size:16pt">''ε''</span><sub>x</sub>=<span style="font-size:16pt">''ε''</span><sub>y</sub>=<span style="font-size:16pt">''ε''</span><sub>z</sub>=0.01 eV/Å. | |||
== Related Tags and Sections == | == Related Tags and Sections == | ||
Revision as of 14:18, 19 March 2011
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.
For LCALCEPS=.TRUE., VASP calculates the ion-clamped static dielectric tensor
- [math]\displaystyle{ \epsilon^\infty_{ij}=\delta_{ij}+ \frac{4\pi}{\epsilon_0}\frac{\partial P_i}{\partial \mathcal{E}_j}, \qquad {i,j=x,y,z} }[/math]
the Born effective charge tensors
- [math]\displaystyle{ 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} }[/math]
and the ion-clamped piezoelectric tensor of the system
- [math]\displaystyle{ e^{(0)}_{ij}=-\frac{\partial \sigma_i}{\partial \mathcal{E}_j}, \qquad {i=xx, yy, zz, xy, yz, zx}\quad{j=x,y,z} }[/math]
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 εx=εy=εz=0.01 eV/Å.
Related Tags and Sections
LEPSILON, LCALCPOL, EFIELD_PEAD, LPEAD, IPEAD, LBERRY, IGPAR, NPPSTR, DIPOL, Berry phases and finite electric fields