Project Planning and Documents

This page contains the plans and outlines the new Basis Set Exchange project.


A rewrite of the current EMSL Basis Set Exchange database and website (

Public Code Repository

The main code for this project is located on GitHub at Comments and bugs/issues should be reported there.

The main documentation is located at

Additional related projects are located under the MolSSI-BSE GitHub organization at


The Basis Set Exchange has served the community well since its inception around 2004. However, the current code stack is considered outdated and in need of a rewrite.

  • The code is currently written in Java, which is considered ‘heavy’ for such a project today.

  • The codebase is considered over-engineered in other ways, including the use of multiple components originally written for other projects and repurposed for the BSE

The actual basis set data is considered de-facto standard by much of the community. Nevertheless, there are errors and inconsistencies. While most errors are believed to be fixed, some may remain due to some inflexibility of the current code stack.

Proposed Components

The new BSE is proposed to have 4 separate components

  1. A store or database of basis set data, in some form

  2. A library accompanying the data, allowing for querying and composing basis set information

  3. An web API for programmatically querying and obtaining basis set data

  4. A web frontend

Backend Data Store

This component contains the actual basis set data in a common format. The old BSE stored basis set data in XML files, while the new BSE will use JSON files, making it more lightweight. This data will be stored in a publicly-accessible git repository on GitHub. This repository is combined with the backend library (see next section). Since the data is stored as (relatively) plain text, modifications to this data can take place through already-established channels and protocols dealing with modifications and conflict resolution (GitHub issues and pull requests, for example). Many people working with basis sets will be familiar with such procedures, and additional help and perhaps web interfaces should be available to those that are not familiar.

Backend Library

This library is responsible for consuming the raw basis set data and producing some useful output. Some aspects of this include:

  • Composing complete basis sets from components (for example, adding polarization or diffuse functions)

  • Converting a basis set to a particular output format (Gaussian or NWChem, for example)

  • Helper functions for curation

  • Schemas and validation functions

  • Basis set manipulation, such as uncontraction and optimization of general contractions.

  • Obtaining notes about basis sets and basis set families

  • Obtaining references for basis sets

Due to the nature of this library, it is combined (in the same version control repository) with the raw basis set data. While this is likely the best path forward, discussion of separation of the data and the library may happen at a later date.

In addition, a command-line interface will also be included as part of this library.


This component is responsible for allowing users to programmatically obtain basis set information via a REST interface.

This interface will mostly mirror the main API of the backend library.

It should be noted that this interface will be read-only, as the curation of the basis set raw data is done elsewhere.

Web Frontend

Many people currently use the web frontend to download and explore basis sets. In general, people approve of the current interface and functionality, with only small improvements desired.

The web fronted should be as separate as possible from the other components, allowing for future changes and possible rewrites.

Data Curation and Identifiers

As part of this project, basis sets will be verified, when possible, against other databases, literature, and what is implemented in various codes. An effort will be made to identify canonical, standard values based on these sources. When differences are found, they will be recorded within the basis set data notes.

This work will support the community in running well-defined, reproducible computations.


A section of the website will be devoted to education about basis sets, including common nomenclature and the best basis sets for different calculations.

Project Members

The project is a collaboration between MolSSI and EMSL/PNNL. The members and major responsibilities are:

  • MolSSI

    • Benjamin Pritchard - Project lead, development of backend library

    • Doaa Altaraway - Development of the web frontend

    • Daniel Smith - Programming support

  • EMSL

    • Tara Gibson - EMSL lead, development support

    • Phil Gackle - Sysadmin/Advisor

    • Eric Bylaska - Subject matter expert

  • Other

    • Theresa Windus - Liaison, MolSSI BoD Sponsor, development support

    • Ellie Fought - Basis set curation support

Community Engagement

Help from the community will likely be required for some parts of the project. In particular, curation and validation of the basis data itself will likely be a community-wide effort, as well as opinions on website design.

In addition, opinions about basis set data and naming will be solicited from basis set authors and the developers of computational chemistry code.

If you would like to help with this project, contact Benjamin Pritchard at

Timelines and Milestones

Current short-to-medium term milestones can be viewed at