# Hybrid functionals

### This page gives hints on how to use hybrid functionals with the ABINIT package.

##### Copyright (C) 2016-2017 ABINIT group (FJ)

Mentioned in help_features#2.2, help_features#5.

### Table of content:

- 1. Introduction.
- 2. Related input variables.
- 3. Selected input files.

### 1. Introduction.

The Fock exchange term has been implemented in ABINIT, both in the norm-conserving pseudopotential framework and in the PAW one. Some details about the implementation in ABINIT can be found here.
For an ABINIT user, to make a calculation of Fock exchange:
- do a first GGA dataset for the ground state
- do a second dataset for the Fock calculation choosing ixc=40-42 (HF, PBE0, PBE0-1/3), -406 (PBE0-Libxc), -456 (PBE0-1/3 Libxc), or -427, -428 (HSE03, HSE06).

The energy and forces are available in the norm-conserving and PAW frameworks. Stresses are available in the norm-conserving framework only for the moment.

WARNING:
Forces and stresses cannot be calculated simultaneously for the moment.
The spin polarised case has not been extensively tested for the moment.
Use istwfk=1, iscf=2, paral_kgb=0, paral_atom=0.
The efficiency of the calculation is not optimal. Work is in progress concerning this point.
Go to the top

### 2. Related input variables.

Compulsory input variables:

... ixc [Index of eXchange-Correlation functional]

Basic input variables:

... fockoptmix [FOCK operator : OPTions for MIXing]

Useful input variables:

... nbandhf [Number of BANDs for (Hartree)-Fock exact exchange]
... nphf [Number of Processors for (Hartree)-Fock exact exchange]

Relevant internal variables:

... %usefock [USE FOCK exact exchange]

Input variables for experts:

... cgtyphf [Conjugate Gradient TYPe used for Hartree Fock exact exchange]
... nkpthf [Number of K - Points for (Hartree) Fock exact exchange]
... nnsclohf [Number of Non-Self Consistent LOops for (Hartree)-Fock exact exchange]
Go to the top

### 3. Selected input files.

WARNING : as of ABINITv8.6.x, the list of input files provided in the specific section of the topics Web pages is still to be reviewed/tuned. In some cases, it will be adequate, and in other cases, it might be incomplete, or perhaps even useless.
The user can find some related example input files in the ABINIT package in the directory /tests, or on the Web:

tests/v7/Input: t65.in t66.in

tests/libxc/Input: t67.in t68.in t69.in

tests/paral/Input: t93.in t94.in
Go to the top