even_handed

Implementation of the even-handed subsystem selection for projection-based embedding.

J. Chem. Phys. 149, 144101 (2018); https://doi.org/10.1063/1.5050533

Basic Procedure:

Run original projection-based embedding calculation using atoms card
- Print out relevant info (overlap and localized molecular orbitals) using MATROP
- Save the localized molecular orbitals (LMOs) of the entire system using the wfu file
Run the even-handed script to determine the correct LMOs to include
- The script can be run by python main.py -d path_to_folder -n output_filename
Restart the embedding calculation from the wfu file
- Run a single iteration DFT calculation on the LMOs from the wfu file. This sets a bunch of global variables in Molpro which are needed for embedding to work properly
- Call the embed command with orbs correctly specified

These rules must be followed otherwise the even-handed script will not work!
Case 1: System size stays constant (e.g. SN2 reaction)
- The atoms of each molecule in the reaction coordinate need to be in the same order in the xyz file
Case 2: Subsystem A size changes
- Use the --b option with main.py so subsystem B is even-handedly selected instead of subsystem A
- Make sure that all subsystem A (active) atoms come first in the xyz file
- Make sure all atoms in subsystem B are in the same order between the product and reactant in their respective xyz files

Plot the densities of the even-handed selection of the subsystems as a visual sanity check
Plot the overlap metrics to ideally see a large separation between the chosen orbitals (an overlap metric approaching 1) and the excluded orbitals (an overlap metric approaching 0)

There is a simple example for an SN2 reaction within data that outlines the basic procedure