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How to obtain AmberTools21

AmberTools is a free, useful standalone package and a prerequisite for installing Amber itself. The AmberTools suite is free of charge, and its components are mostly released under the GNU General Public License (GPL). A few components are included that are in the public domain or which have other, open-source, licenses. The libsander and libpbsa libraries use the LGPL license.

Option 1: Upgrading from AmberTools20

If you already have AmberTools20 installed from source, just do this:

  cd amber20_src
  ./update_amber --upgrade
  cd build
  make install

Option 2: Binary distribution via conda

The conda package-management system can install a serial, binary (pre-compiled) distribution. This should work for Linux and MacOS systems, and may be sufficient for many users. It provides a simple way to get started with AmberTools, and to install it into many workflows. It does not provide access to parallel or GPU-enabled options, and the full source-code distributions are needed if you wish to combine AmberTools with Amber.

To install, proceed as follows:

  • If you don't have conda installed, please visit the Miniconda download page.

  • Those with an existing conda installation may wish to create a new conda "environment" to avoid conflicts with what you already have installed. To do this:

      conda create --name AmberTools21
      conda activate AmberTools21

    (Note that you would need to perform the "conda activate" step every time you wish use AmberTools21 in a new terminal; it might be appropriate to add this to your start-up script. Creating a new environment should not be necessary if you only use conda for AmberTools.)

  • Once this is done, type:

      conda install -c conda-forge ambertools=21 compilers

  • AmberTools is updated from time to time. To keep your conda package up-to-date, do this:

      conda update -c conda-forge ambertools

Thanks to Jaime Rodríguez-Guerra, the Chodera lab, and Simon Bray for spearheading this.

Option 3: Getting source code in tar format

This path is for users to do not already have AmberTools20, and is the traditional way AmberTools has been distributed. AmberTools is distributed in source code format, and must be compiled in order to be used. You will need C, C++ and Fortran90 compilers.

The Reference Manual is available in pdf format, and included in the distribution. It may help you to see if AmberTools meets your needs.

To download version 21 of the AmberTools distribution, please fill in the following form and click the "Download" button. The file size you should get is about 500 MB, and the md5sum is 81bd97be0aa9d3e728f2db5f63987e04.

Note: Installation instructions are in Chapter 2 of the Amber 2021 Reference Manual. More detailed instructions for many machines may be found at simplified requirements for MacOS, Linux and Windows 10.




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How to obtain Amber20

Amber20 facilitates faster simulations (on parallel CPU or GPU hardware) and is distributed with a separate license and fee structure. Click here for the Amber 20 License Agreement (PDF). Print this form, fill it out, sign and return (with your payment) to the address given at the bottom of the license agreement. Once your order is processed, you will receive download information via email. PDF versions of the Reference Manual are included in the download.

Please note: The Amber20 license is a site license, valid for any number of users and any number of computers. The computers may be located anywhere (such as in the "cloud", or at remote computing centers.) There are restrictions on using the codes on behalf of others who do not have an Amber license; see the license document for details.

Also note: Each release of Amber (which happens every two years) is treated as separate product, and requires a new license form and a new fee.


  • Academic/non-profit/government: $500 (US dollars).
  • Industrial (for-profit): $20,000 for new licensees, $15,000 for licensees of Amber 18.
  • Porting and demonstration licenses are available, as are licenses for computing centers: see the License Agreement for details.
  • Custom payment schedules or subscription-based approaches can be arranged: please send email to for more information.)

  • People who licensed Amber18 after January 1, 2020 are eligible for a free upgrade to Amber20. (This is not automatic: if you wish to obtain the new version, you need fill out and submit a new License Agreement, indicating that you are eligible for the upgrade.)

Payment for all orders for Amber must received prior to shipment of the Software. Payment must be via bank transfer, paper bank check or paper money order in USD, or Visa, MasterCard or American Express credit card. Make payments to: Regents, University of California. We are sorry, but purchase orders can no longer be accepted.

Once payment is received, an email will be sent to the address provided by the customer on the License Agreement containing a username and password, along with instructions on how to download the software.

Fee Waivers

Waivers for the license fee are available for scientists outside of North America, Western Europe and Japan. Please send email to, explaining your situation, and your need for the pmemd program (all other parts of Amber are available for free).

"How's that for maxed out?"

Last modified: Aug 31, 2021