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. GBRV 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/$ID_pbe_v1.2.uspp
ion-species GBRV/$ID_pbe_v1.01.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. SG15 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/$ID_ONCV_PBE-1.1.upf
ion-species SG15/$ID_ONCV_PBE-1.0.upf
```
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