This glossary contains the common terms which appear over the entire Fractal project. There are other, specialized glossaries for components of Fractal which are linked below to help group terms together with their contextual docs. Some terms may appear in multiple glossaries, but will always have the same meaning, e.g. Queue Adapter and Adapter.

DB Index

A DB Index (or Database Index) is a commonly queried field used to speed up searches in a DB Table.

DB Socket

A DB Socket (or Database Socket) is the interface layer between standard Python queries and raw SQL or MongoDB query language.

DB Table

A set of data inside the Database which has a common ObjectId. The table name follows SQL conventions which is also known as a collection in MongoDB.

Fractal Config Directory

The directory where QCFractal Server and Database configuration files live. This is also the home of the Database itself in the default configuration. Default path is ~/.qca/qcfractal

Hash Index

A index that hashes the information contained in the object in a reproducible manner. This hash index is only used to find duplicates and should not be relied upon as it may change in the future.


A unique 3D representation of a molecule. Any changes to the protonation state, multiplicity, charge, fragments, coordinates, connectivity, isotope, or ghost atoms represent a change in the molecule.


A ObjectId (or Database ID) is a unique ID for a given row (a document or entry) in the database that uniquely defines that particular row in a DB Table. These rows are automatically generated and will be different for every database, but outlines ways to reference other rows in the database quickly. A ObjectId is unique to a DB Table.


On-node computations, these can either be a single computation (energy, gradient, property, etc.) or a series of calculations such as a geometry optimization.

Queue Adapter

The interface between QCFractal’s internal queue representation and other queueing systems such as Dask or Fireworks. Also see the Adapter in the Manager glossary.


Iterative workflows where the required computations are distributed via the queue and then are processed on the server to acquire the next iteration of calculations.

Contextually Organized Glossaries