A Parallel Fock-Space ab DMRG code based on MPO for Quantum Chemistry Hamiltonian

Basic ideas:

1. The central quantity is the three indexed operators in MPO format.

2. Parallelization is achieved at the operator level.

Supports:

1. Ab inito DMRG with/without particle number and Sz symmetry

2. Spin-projected DMRG with S^2 symmetry

3. Conversion form spin-projected MPS to spin-adapted MPS used in the BLOCK code [for examples, see source/samps/example_conversion/]

Reference:

Spin-Projected Matrix Product States: Versatile Tool for Strongly Correlated Systems

Z. Li and G.K.-L. Chan, J. Chem. Theory Comput., 2017, 13 (6), pp 2681–2695