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QUBEKit - Quantum Mechanical Bespoke force field toolkit

Newcastle University UK - Cole Group

Status Language grade: Python Build Status Conda (channel only)
Foundation License: MIT Python Version platforms
Installation Anaconda-Server Badge Anaconda-Server Badge Anaconda-Server Badge

Table of Contents

What is QUBEKit?

QUBEKit is a Python 3.6+ based force field derivation toolkit for Linux operating systems. Our aims are to allow users to quickly derive molecular mechanics parameters directly from quantum mechanical calculations. QUBEKit pulls together multiple pre-existing engines, as well as bespoke methods to produce accurate results with minimal user input. QUBEKit aims to avoid fitting to experimental data where possible while also being highly customisable.

Users who have used QUBEKit to derive any new force field parameters should cite the following papers:

In Development

QUBEKit should currently be considered a work in progress. While it is stable we are constantly working to improve the code and broaden its compatibilities.

We use lots of software written by many different people; if reporting a bug please (to the best of your ability) make sure it is a bug with QUBEKit and not with a dependency. We welcome any suggestions for additions or changes.


QUBEKit is now available through conda-forge; this is the recommended installation method. Github has our latest version which will likely have newer features but may not be stable. Pip is not updated as regularly as Anaconda or Github but should also be stable.

# Recommended
conda install -c conda-forge qubekit

# Alternative 
pip install qubekit

# Recommended for Developers (see below)
git clone
cd <install location>
python install    


Download Anaconda from the above link and install with the linux command:


You may need to use chmod +x Anaconda3<version>.sh to make it executable.

We recommend you add conda to your .bashrc when prompted.

Installation of Gaussian is likely handled by your institution; QUBEKit uses it for density calculations only. If you don't plan on performing these sorts of calculations then it is not necessary. If you do, please make sure Gaussian09 is executable with the command g09.

Chargemol can be downloaded and installed from a zip file in the above link. Be sure to add the path to the QUBEKit configs once you've generated them (explanation).

Most conda packages are included in the conda-forge install. Packages not available through conda-forge may need to be installed separately.

conda install -c conda-forge qubekit

The following table details some of the core requirements included in the conda install of QUBEKit. If any packages are missing from the install or causing issues, this table shows how to get them.

Package Conda Install
GeomeTRIC conda install -c conda-forge geometric
OpenForceField conda install -c omnia openforcefield
OpenMM conda install -c omnia openmm
PSI4 conda install -c psi4 psi4
QCEngine conda install -c conda-forge qcengine
RDKit conda install -c rdkit rdkit
TorsionDrive conda install -c conda-forge torsiondrive

Adding lots of packages can be a headache. If possible, install using Anaconda through the terminal. This is generally safest, as Anaconda should deal with versions and conflicts in your environment. Generally, conda packages will have the conda install command on their website or github. For the software not available through Anaconda, or if Anaconda is having trouble resolving conflicts, either git clone them and install:

git clone https://<git_address_here>
cd <location of cloned package>
python install

or follow the described steps in the respective documentation.

Installing as dev

If downloading QUBEKit to edit the latest version of the source code, the easiest method is install via conda, then remove the conda version of qubekit and git clone. This is accomplished with a few simple commands:

# Install QUBEKit as normal
conda install -c conda-forge qubekit

# Remove ONLY the QUBEKit package itself, leaving all dependencies installed
# and on the correct version
conda remove --force qubekit

# Re-download the latest QUBEKit through github
git clone

# Re-install QUBEKit outside of conda
cd QUBEKit/
python install


Below is general help for most of the commands available in QUBEKit. There is some short help available through the terminal (invoked with -h) but all necessary long-form help is within this document.

Config files

QUBEKit has a lot of settings which are used in production and changing these can result in very different force field parameters. The settings are controlled using ini style config files which are easy to edit. After installation you should notice a QUBEKit_configs folder in your main home directory; now you need to create a master template. To do this, use the command QUBEKit -setup where you will be presented with the following:

You can now edit config files using QUBEKit, chose an option to continue:
1) Edit a config file
2) Create a new master template
3) Make a normal config file

Choose option two to set up a new template which will be used every time you run QUBEKit (unless you supply the name of another ini file in the configs folder). The only parameter that must be changed for QUBEKit to run is the Chargemol path in the descriptions section. This option is what controls where the Chargemol code is accessed from on your PC. It should be the location of the Chargemol home directory, plus the name of the Chargemol folder itself to account for version differences:


Following this, feel free to change any of the other options such as the basis set.

QUBEKit does have a full suite of defaults built in. You do not necessarily need to create and manage an ini config file; everything can be done through the terminal commands. To make it easier to keep track of changes however, we recommend you do use a config file, or several depending on the analysis you're doing.

You can change which config file is being used at runtime using the command:

-config <config file name>.ini

Otherwise, the default master_config.ini will be used.

QUBEKit Commands: Running Jobs

Running a job entirely on defaults, is as simple as typing -i for input, followed by the pdb file name, for example:

QUBEKit -i methane.pdb

This will perform a start-to-finish analysis on the methane.pdb file using the default config ini file. For anything more complex, you will need to add more commands.

Given a list of commands, such as: -setup, -progress some are taken as single word commands. Others however, such as changing defaults: (-c 0), (-m 1), are taken as tuple commands. The first command of tuple commands is always preceded by a -, while the latter commands are not: (-skip density charges). (An error is raised for 'hanging' commands e.g. -c, 1 or -sm.)

All commands can be provided in any order, as long as tuple commands are paired together. All configuration commands are optional. If nothing at all is given, the program will run entirely with defaults. QUBEKit only needs to know the molecule you're analysing, given with -i <molecule>.pdb or -sm <smiles string>.

Files to be analysed must be written with their file extension (.pdb) attached or they will not be recognised commands. All commands should be given in lower case with two main exceptions; you may use whatever case you like for the name of files (e.g. -i DMSO.pdb) or the name of the directory (e.g. -log Run013).

QUBEKit Commands: Some Examples

A full list of the possible command line arguments is given below in the Cook Book section. This section covers some simple examples

Running a full analysis on molecule.pdb with a non-default charge of 1, the default charge engine Chargemol and with GeomeTRIC off: Note, ordering does not matter as long as tuples commands (-c 1) are together.

-i is for the input, -c denotes the charge and -geo is for (en/dis)abling geomeTRIC.

QUBEKit -i molecule.pdb -c 1 -geo false
QUBEKit -c 1 -geo false -i molecule.pdb

Running a full analysis with a non-default bonds engine: Gaussian09 (g09):

QUBEKit -i molecule.pdb -bonds g09

The program will tell the user which defaults are being used, and which commands were given. Errors will be raised for any invalid commands and the program will not run. A full log of what's happening will be created in a QUBEKit_log.txt file.

Try running QUBEKit with the command:

QUBEKit -sm C methane -end hessian

This will generate a methane pdb file (and mol file) using its smiles string: C, then QUBEKit will analyse it until the hessian is calculated. See QUBEKit Commands: Custom Start and End Points (single molecule) below for more details on -end.

QUBEKit Commands: Logging

Each time QUBEKit runs, a new working directory containing a log file will be created. The name of the directory will contain the run number or name provided via the terminal command -log (or the run number or name from the configs if a -log command is not provided). This log file will store which methods were called, how long they took, and any docstring for them (if it exists). The log file will also contain information regarding the config options used, as well as the commands given and much more. The log file updates in real time and contains far more information than is printed to the terminal during a run. If there is an error with QUBEKit, the full stack trace of an exception will be stored in the log file.

The error printed to the terminal may be different and incorrect so it's always better to check the log file.

Many errors have custom exceptions to help elucidate if, for example, a module has not been installed correctly.

The format for the name of the active directory is:


If using QUBEKit multiple times per day with the same molecule, it is therefore necessary to update the 'run number'. Not updating the run number when analysing the same molecule on the same day will prevent the program from running. This is to prevent the directory being overwritten.

Updating the run number can be done with the command:

-log Prop1201

where Prop1201 is an example string which can be almost anything you like (no spaces or special characters).

Inputs are not sanitised so code injection is possible but given QUBEKit's use occurs locally, you're only hurting yourself! If you don't understand this, don't worry, just use alphanumeric log names like above.

QUBEKit Commands: High Throughput

Bulk commands are for high throughput analysis; they are invoked with the -bulk keyword. A csv must be used when running a bulk analysis. If you would like to generate a blank csv config file, simply run the command:

QUBEKit -csv example.csv

where example.csv is the name of the config file you want to create. This will automatically generate the file with the appropriate column headers. The csv config file will be put into wherever you ran the command from. When writing to the csv file, append rows after the header row, rather than overwriting it.

If you want to limit the number of molecules per csv file, simply add an argument to the command. For example, if you have 23 pdb files and want to analyse them 12 at a time, use the command:

QUBEKit -csv example.csv 12

This will generate two csv files, one with 12 molecules inside, the other with the remaining 11. You can then fill in the rest of the csv as desired, or run immediately with the defaults.

Before running a bulk analysis, fill in each column for each molecule*; importantly, different config files can be supplied for each molecule.

*Only the name column needs to be filled (which is filled automatically with the generated csv), any empty columns will simply use the default values:

  • If the charge column is empty, charge will be set to 0;
  • If the multiplicity column is empty, multiplicity will be set to 1;
  • If the config column is empty, the default config is used;
  • The smiles string column only needs to be filled if a pdb is not supplied;
  • Leaving the restart column empty will start the program from the beginning;
  • Leaving the end column empty will end the program after a full analysis.

A bulk analysis is called with the -bulk command, followed by the name of the csv file:

QUBEKit -bulk example.csv

Any pdb files should all be in the same place: where you're running QUBEKit from. Upon executing this bulk command, QUBEKit will work through the rows in the csv file. Each molecule will be given its own directory and log file (the same as single molecule analyses).

Please note, there are deliberately two config files. The changeable parameters are spread across a .csv and a .ini config files. The configs in the .ini are more likely to be kept constant across a bulk analysis. For this reason, the .csv config contains highly specific parameters such as torsions which will change molecule to molecule. The .ini contains more typically static parameters such as the basis sets and engines being used (e.g. PSI4, Chargemol, etc). If you would like the ini config to change from molecule to molecule, you may specify that in the csv config.

You can change defaults inside the terminal when running bulk analyses, and these changed defaults will be printed to the log file. However, the config files themselves will not be overwritten. It is therefore recommended to manually edit the config files rather than doing, for example:

QUBEKit -bulk example.csv -log run42 -ddec 3 -solvent true

Be aware that the names of the pdb files are used as keys to find the configs. So, each pdb being analysed should have a corresponding row in the csv file with the correct name (if using smiles strings, the name column will just be the name given to the created pdb file).

For example (csv row order does not matter, and you do not need to include smiles strings when a pdb is provided; column order does matter):



QUBEKit Commands: Custom Start and End Points (single molecule)

QUBEKit also has the ability to run partial analyses, or redo certain parts of an analysis. For a single molecule analysis, this is achieved with the -end and -restart commands.

The stages are:

Stage Description
parametrise The molecule is parametrised using OpenFF, AnteChamber or an xml file. This step also loads in the molecule and extracts key information like the atoms and their coordinates.
mm_optimise This is a quick, preliminary optimisation which speeds up later optimisations. (This stage is skippable.)
qm_optimise This is the main quantum mechanical optimisation stage; default method is to use PSI4 with GeomeTRIC.
hessian This again uses PSI4 or Gaussian to calculate the Hessian matrix which is needed for calculating bonding parameters.
mod_sem Using the Hessian matrix, the bond lengths, angles and force constants are calculated with the Modified Seminario Method.
density The density is calculated using Gaussian09. This is where the solvent is applied as well (if configured).
charges The charges are partitioned and calculated using Chargemol with DDEC3 or 6.
lennard_jones The charges are extracted and Lennard-Jones parameters (sigma and epsilon) are calculated.
torsion_scan Using the molecule's geometry, a torsion scan is performed. The molecule can then be optimised with respect to these parameters.
torsion_optimise The fitting and optimisation step for the torsional analysis.
finalise This step (which is always performed, regardless of end-point) produces an xml file for the molecule. This stage also prints the final information to the log file and a truncated version to the terminal.

In a normal run, all of these stages are executed sequentially, but with -end and -restart you are free to run from any step to any step inclusively.

When using -end, simply specify the end-point in the proceeding command (default finalise), when using -restart, specify the start-point in the proceeding command (default parametrise). The end-point (if not finalise) can then be specified with the -end command.

When using these commands, all other config-changing commands can be used in the same ways as before. For example:

QUBEKit -i methanol.pdb -end charges
QUBEKit -restart qm_optimise -end density
QUBEKit -i benzene.pdb -log BEN001 -end charges -geo false 
QUBEKit -restart hessian -ddec 3

If using -end but not -restart, a new directory and log file will be created within wherever the command is run from. Just like a normal analysis.

However, using -restart requires files and other information from previous executions. Therefore, -restart can only be run from inside a directory with those files present.

Note: you do not need to use the -i (input file) command when restarting, QUBEKit will detect the pdb file for you.

To illustrate this point, a possible use case would be to perform a full calculation on the molecule ethane, then recalculate using a different (set of) default value(s):

QUBEKit -i ethane.pdb -log ETH001
cd QUBEKit_ethane_2019_01_01_ETH001
QUBEKit -restart density -end charges -ddec 3

Here, the calculation was performed with the default DDEC version 6, then rerun with version 3 instead, skipping over the early stages which would be unchanged. It is recommended to copy (not cut) the directory containing the files because some of them will be overwritten when restarting.

Note that because -restart was used, it was not necessary to specify the pdb file name with -i.

QUBEKit Commands: Skipping Stages

There is another command for controlling the flow of execution: -skip. The skip command allows you to skip any number of proceeding steps. This is useful if using a method not covered by QUBEKit for a particular stage, or if you're just not interested in certain time-consuming results.

-skip takes at least one argument and on use will completely skip over the provided stage(s). Say you are not interested in calculating bonds and angles, and simply want the charges; the command:

QUBEKit -i acetone.pdb -skip hessian mod_sem

will skip over the Hessian matrix calculation which is necessary for the modified Seminario method (skipping that too). QUBEKit will then go on to calculate density, charges and so on.

Beware skipping steps which are required for other stages of the analysis.

Just like the other commands, -skip can be used in conjunction with other commands like config changing, and -end or -restart. Using the same example above, you can stop having calculated charges:

QUBEKit -i acetone.pdb -skip hessian mod_sem -end charges

-skip is not available for -bulk commands and probably never will be. This is to keep bulk commands reasonably simple. We recommend creating a simple script to run single analysis commands if you would like to skip stages frequently.

In case you want to add external files to be used by QUBEKit, empty folders are created in the correct place even when skipped. This makes it easy to drop in, say, a .cube file from another charges engine, then calculate the Lennard-Jones parameters with QUBEKit.

QUBEKit Commands: Custom Start and End Points (multiple molecules)

When using custom start and/or end points with bulk commands, the stages are written to the csv file, rather than the terminal. If no start point is specified, a new working directory and log file will be created. Otherwise, QUBEKit will find the correct directory and log file based on the log string and molecule name. This means the log string cannot be changed when restarting a bulk run. There will however be a clear marker in the log file, indicating when an analysis was restarted.

Using a similar example as above, two molecules are analysed with DDEC6, then restarted for analysis with DDEC3:


QUBEKit -bulk first_run.csv

(optional: copy the folders produced to a different location to store results)


QUBEKit -bulk second_run.csv

The first execution uses a config file for DDEC6 and runs from the beginning up to the charges stage. The second execution uses a config file for DDEC3 and runs from the density stage to the charges stage.

QUBEKit Commands: Checking Progress

Throughout an analysis, key information will be added to the log file. This information can be quickly parsed by QUBEKit's -progress command

To display the progress of all analyses in your current directory and below, use the command:

QUBEKit -progress

QUBEKit will find the log files in all QUBEKit directories and display a colour-coded table of the progress.

Indicator Meaning
Completed successfully
~ Neither finished nor errored
S Skipped
E Started and failed for some reason

Viewing the QUBEKit log file will give more information as to why it failed.

QUBEKit Commands: Other Commands and Information

You cannot run multiple kinds of analysis at once. For example:

QUBEKit -bulk example.csv -i methane.pdb -bonds g09

is not a valid command. These should be performed separately:

QUBEKit -bulk example.csv
QUBEKit -i methane.pdb -bonds g09

Be wary of running QUBEKit concurrently through different terminal windows. The programs QUBEKit calls often just try to use however much memory is assigned in the config files; this means they may try to take more than is available, leading to a crash.

Cook Book

Complete analysis of single molecule from its pdb file using only defaults:

QUBEKit -i molecule.pdb

All commands can be viewed by calling QUBEKit -h. Below is an explanation of what all these commands are:

Command Type Description
-geo Bool: True, true, t, False, false, f Enable or disable GeomeTRIC
-ddec Int: 3, 6 Change DDEC version
-solvent Bool Enable or disable the solvent model
-param String: antechamber, openff, xml Change the method for initial parametrisation
-log String: <arbitrary alphanumeric> Change the log file name and directory label
-func String: <any valid PSI4/Gaussian functional Change the functional being used
-basis String: <any valid PSI4/Gaussian basis set Change the basis set
-vib Float: 0.0 - 1.0 Change the vibrational scaling used with the basis set
-memory Int: 1 - PC limit Change the amount of memory allocated
-threads Int: 1 - PC limit Change the number of threads allocated
-v Bool Change the verbosity of the output

Complete analysis of ethane from its smiles string using DDEC3, OpenFF and no solvent (-log command labels the analysis):

QUBEKit -sm CC -ddec 3 -param openff -solvent false -log ethane_example

Analyse benzene from its pdb file until the charges are calculated; use DDEC3:

QUBEKit -i benzene.pdb -end charges -ddec 3 -log BENZ_DDEC3

Redo that analysis but use DDEC6 instead:

(Optional) Copy the folder and change the name to indicate it's for DDEC6:

cp -r QUBEKit_benzene_2019_01_01_BENZ_DDEC3 QUBEKit_benzene_2019_01_01_BENZ_DDEC6

(Optional) Move into the new folder:

cd QUBEKit_benzene_2019_01_01_BENZ_DDEC6

Rerun the analysis with the DDEC version changed. This time we can restart just before the charges are calculated to save time. Here we're restarting from density and finishing on charges:

QUBEKit -restart density -end charges -ddec 6

This will still produce an xml in the finalise folder.

Analyse methanol from its smiles string both with and without a solvent:

QUBEKit -sm CO -solvent true -log Methanol_Solvent

(Optional) Create and move into new folder

cp -r QUBEKit_methanol_2019_01_01_Methanol_Solvent QUBEKit_methanol_2019_01_01_Methanol_No_Solvent
cd QUBEKit_methanol_2019_01_01_Methanol_No_Solvent

QUBEKit -solvent false -restart density

Calculate the density for methane, ethane and propane using their pdbs:

Generate a blank csv file with a relevant name:

QUBEKit -csv density.csv

Fill in each row like so:


Run the analysis:

QUBEKit -bulk density.csv

Note, you can add more commands to the execution but it is recommended that changes are made to the config files instead.

Running the same analysis but using the smiles strings instead; this time do a complete analysis:

Generate a blank csv with the name simple_alkanes:

QUBEKit -csv simple_alkanes.csv

Fill in the csv file like so:


Run the analysis:

QUBEKit -bulk simple_alkanes.csv

Just calculating charges for acetone:

Skip hessian and mod_sem, the two stages used to calculate the bonds and angles, then end the analysis after the charge calculation.

QUBEKit -i acetone.pdb -skip hessian mod_sem -end charges


Quantum Mechanical Bespoke Force Field Derivation Toolkit







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