Like most other plane-wave codes, JDFTx deals only with the valence electrons. The effect of core electrons are handled through the use of pseudopotentials.

Currently, three formats of pseudopotentials are supported by JDFTx: ABINIT .fhi format (norm-conserving), Vanderbilt .uspp format (Ultrasoft) and the Quantum Espresso (QE) UPF format (norm-conserving and ultrasoft). The QE UPF files must be of the version 2.0.1 format; older versions may be converted using the upf2upf2 utility in the QE distribution.

Use of reliable, robust and transferable pseudopotentials is an essential part of any density-functional calculation using plane-waves.

Here are some pseudopotential libraries and generators that work with JDFTx:

GBRV Library

Garrity-Bennett-Rabe-Vanderbilt library is a library of ultrasoft pseudopotentials for most of the periodic table, with the exception of f-block elements. See http://www.physics.rutgers.edu/gbrv and Ref. [10] for more information about the design, construction and testing of these pseudopotentials. These pseudopotentials are pre-distributed with JDFTx, and you can access the latest version for any element using the wildcard syntax:
```
ion-species GBRV/$ID_pbe.uspp
```
for the PBE pseudeopotentials, and similarly using GBRV/$ID_lda.uspp or GBRV/$ID_pbesol.uspp for the LDA and PBEsol pseudeopotentials respectively.

Some pseudopotentials have multiple version numbers installed: a subset of v1, v1.01, v1.1, v1.2, v1.4 and v1.5 for each element. You can select older versions by explicitly selecting version numbers eg. to only use the latest among v1 or v1.4 but none of the others:
```
ion-species GBRV/$ID_pbe_v1.4.uspp
ion-species GBRV/$ID_pbe_v1.uspp
```
SG15 Library

Schlipf-Gygi 2015 library is a library of norm-conserving pseudopotentials for most of the periodic table, with the exception of f-block elements. See http://www.quantum-simulation.org and Ref. [26] for more information about the design, construction and testing of these pseudopotentials. These pseudopotentials are pre-distributed with JDFTx, and you can access the latest version for any element using the wildcard syntax:
```
ion-species SG15/$ID_ONCV_PBE.upf
```
Some pseudopotentials have multiple version numbers installed: a subset of 1.0 and 1.1 for each element. You can select to use specific versions by explicitly specifying version numbers, eg.
```
ion-species SG15/$ID_ONCV_PBE-1.0.upf
```
to only use the 1.0 version.
Virtual Vault for Pseudopotentials and PAW Datasets

NNIN Virtual Vault is a database of pseudopotentials organized by Derek Stewart at Cornell Nanoscale Facility: http://nninc.cnf.cornell.edu (The fhi and upf format files may be used)
Quantum Espresso pseudopotential library

Norm-conserving and ultrasoft UPF pseudopotentials from the QE collection may be used with JDFTx.
Opium Pseudopotential Generator

Opium is a code to generate norm-conserving pseudopotentials: http://opium.sourceforge.net. Dump results in .fhi format to use with JDFTx.
Bennett & Rappe Pseudopotential Library

Bennett & Rappe is a library of norm-conserving pseudopotentials generated with the Opium code. Available as .fhi files as well as Opium input files (.param).
- LDA: http://www.sas.upenn.edu/rappegroup/research/pseudo-potential-lda.html
- GGA: http://www.sas.upenn.edu/rappegroup/research/pseudo-potential-gga.html