FCI and GENCI initial core guess determinants for Davidson-Liu solver

[marink2]

Description

PR incorporates the feature to run a FCI (or GENCI) calculation(s) with core-excited determinants as the initial guess space for the Davidson-Liu solver. Core-excited determinants include determinant strings with single- and none-occupation on the first position.

User Notes

• [x] Added default boolean parameter (bool core_guess) to StateInfo class.

• [x] Added protected boolean member variable (core_guess_) to ActiveSpaceMethod class.

• [x] ActiveSpaceSolver assigns values of DL_CORE_INITIAL_GUESS to StateInfo object, StateInfo maps this value to ActiveSpaceMethod, which passes value to GENCI or FCI solver.

• [x] Feature is implemented for GENCI and FCI solvers only.

• [x] Included two test cases, fci-core-1 and fci-core-2, for the implemented feature.

• [x] Added default boolean parameter (bool core_guess) to find_initial_guess_det member function of Forte. This feature prints the value(s) of DL_CORE_INITIAL_GUESS in an appropriate place ("Initial Guess") of the output.dat file. To avoid cluttering the parameter list of this function consider creating an instance of ActiveSpaceMethod in sparce_ci_initial_guess.cc.

Checklist

• [x] Added/updated tests of new features and included a reference output.ref file
• [x] Documented source code
• [x] Documented new features in the manual
• [x] Ready to go!

[huangm29]

Please ensure your "User Notes" and "Checklist" correspond to your changes. See other PR for examples.