# Spin-Network-Scaled MP2 (SNS-MP2) by D. E. Shaw¶

Code author: D. E. Shaw Research

Section author: Shannon E. Houck

This plugin is an implementation of the SNS-MP2 algorithm developed by McGibbon et. al. [McGibbon:2017:161725]. The SNS-MP2 method uses neural networking to improve the accuracy of MP2 (dfmp2) interaction energies for dimer molecules. The plugin is distributed under the 2-clause BSD license.

## Installation¶

Binary

• snsmp2 is available as a conda package for Linux and macOS (and Windows, through the Ubuntu shell).

• If using the Psi4conda installer, snsmp2 has already been installed alongside.

• If using the PSI4 conda package, the snsmp2 conda package can be obtained through conda install snsmp2 -c psi4 or conda install psi4-rt -c psi4.

• If using PSI4 built from source, and anaconda or miniconda has already been installed (instructions at Quick Installation), snsmp2 can be obtained through conda install snsmp2 -c psi4. Then, hint its location with PYTHONPATH.

• To remove a conda installation, conda remove snsmp2.

Source

>>> git clone https://github.com/DEShawResearch/sns-mp2

• Once dowloaded, the plugin can be installed as outlined in the documentation:

>>> cd {top-level-sns-mp2-directory}
>>> PSI4_PYTHON=$(head$(which psi4) -n 1 | sed -r 's/^.{2}//')
>>> \$PSI4_PYTHON -m pip install .


## Sample Input¶

A sample input file, adapted from the documentation, is shown below:

 1 2 3 4 5 6 7 8 9 # Sample SNS-MP2 calculation for two helium atoms molecule dimer { He 0 0 0 -- He 2 0 0 } energy('sns-mp2') 

Note that the two monomers are separated by double dashes, indicating that they should be treated as separate molecules. (See sec:analysis-of-intermolecular-interactions for more details on setting up dimer molecules.) This input file can be run in the usual fashion:

>>> psi4 input.dat