Requests for technical support from the VASP group should be posted in the VASP-forum.

# LFOCKACE

LFOCKACE = .TRUE. | .FALSE.
Default: LFOCKACE = .TRUE.

 Default: LFOCKACE = .TRUE. for VASP.6 = N/A for VASP.5.X and older

Description: LFOCKACE determines whether the Adaptively Compressed Exchange Operator is used.[1]

• N.B.:Available for CPU and OpenACC version of VASP.6 when compiled with -Dfock_dblbuf.

For LFOCKACE=.TRUE. the Cholesky decomposition ${\displaystyle X=LL^{\dagger }}$ of the Fock exchange matrix ${\displaystyle X_{ij}=\langle {\tilde {\psi }}_{i}\mid {\tilde {V}}_{X}\mid {\tilde {\psi }}_{j}\rangle }$ is calculated and the adaptively compressed exchange operator ${\displaystyle {\tilde {V}}_{ACE}=-\sum _{i}\mid {\tilde {X}}_{i}\rangle \langle {\tilde {X}}_{i}\mid }$ is used for the action of the Fock exchange on the pseudo orbitals. This method can be used for hybrid functionals in combination with the Davidson algorithm (ALGO=Normal) to save a factor of ${\displaystyle \approx 3}$ in computation time.

For LFOCKACE=.TRUE. the conventional orbital representation is used.