LPEAD: Difference between revisions

From VASP Wiki
No edit summary
Line 49: Line 49:


== Related Tags and Sections ==
== Related Tags and Sections ==
{{TAG|LPEAD}},
{{TAG|IPEAD}},
{{TAG|IPEAD}},
{{TAG|LEPSILON}},
{{TAG|LEPSILON}},
{{TAG|LOPTICS}},
{{TAG|LOPTICS}},
{{TAG|LCALCEPS}},
{{TAG|EFIELD_PEAD}},
[[Berry_phases_and_finite_electric_fields|Berry phases and finite electric fields]]
[[Berry_phases_and_finite_electric_fields|Berry phases and finite electric fields]]
----
----

Revision as of 17:53, 20 March 2011

LPEAD = .TRUE. | .FALSE
Default: LPEAD = .FALSE. 

Description: for LPEAD=.TRUE., the derivative of the cell-periodic part of the orbitals w.r.t. k, |∇kunk⟩, is calculated using finite differences.


The derivative of the cell-periodic part of the orbitals w.r.t. k, k, |∇kunk⟩, may be written as:

where H(k) and S(k) are the Hamiltonian and overlap operator for the cell-periodic part of the orbitals, and the sum over n´ must include a sufficiently large number of unoccupied states.

It may also be found as the solution to the following linear Sternheimer equation (see LEPSILON):

Alternatively one may compute |∇kunk⟩ from finite differences:

where m runs over the N occupied bands of the system, Δk=kj+1-kj, and

.

As mentioned in the context of the self-consistent response to finite electric fields one may derive analoguous expressions for |∇kunk⟩ using higher-order finite difference approximations.

When LPEAD=.TRUE., VASP will compute |∇kunk⟩ using the aforementioned finite difference scheme. The order of the finite difference approximation can be specified by means of the IPEAD-tag (default: IPEAD=4).

These tags may be used in combination with LOPTICS=.TRUE. and LEPSILON=.TRUE..

Related Tags and Sections

IPEAD, LEPSILON, LOPTICS, LCALCEPS, EFIELD_PEAD, Berry phases and finite electric fields


Contents