Draft instructions for using NWChem with chem library

contrib/quasar/README.md

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+Using NWChem with Microsoft Quantum Development Kit
+===================================================
+
+Instructions on building and running NWChem are available
+[here](http://www.nwchem-sw.org/index.php/Main_Page).
+
+Alternatively, you can run the NWChem docker image using the
+instructions at:
+
+<to be filled in>
+
+The general format of NWChem input files is described
+[here](https://github.com/nwchemgit/nwchem/wiki). You can also start
+with any of the input files in `QA/chem_library_tests` in the NWChem
+repository.
+
+## NWChem Input File Format
+
+To generate inputs to Microsoft QDK, the NWChem input file currently
+needs to have the following components:
+
+* `echo` directive to capture geometry and basis set information
+
+* `set tce:print_integrals T` directive to obtain one and two electron integrals
+
+* `set tce:qorb <#orbitals>` directive specifying number of orbitals
+
+* `set tce:qela  <#alpha electrons>` directive specifying number of alpha electrons
+
+* `set tce:qelb  <#beta electrons>` directive specifying number of alpha electrons
+
+* `tce` block with `ccsd` directive is needed to obtain initial state
+  suggestions and reference energies
+
+mcscf can be used to extract representative FCI energies. In the
+absence of mcscf, tce ccsd energies will be used instead.
+
+## Generating QDK Input
+
+The output file from running NWChem can be used to generate input to
+Microsort QDK using the `export_chem_library_yaml.py` script in this
+directory as:
+
+`$python3 export_chem_library_yaml.py < <nwchem_output_file> > <yaml_output>`
+