18.2. The RSF module with various CC reference functions

Please, first read the Quick Guide on all available RSF-CC methods here.

Since most of the RSF-CC flavors implemented in PyBEST offer similar functionality, all features mentioned below are applicable to all RSF-CC methods if not mentioned otherwise. All modules support only the Davidson diagonalization of the EOM Hamiltonian.

In addition to the IOData container attributes mentioned in the Quick Guide above, the RSFBase containers include the following information

orb_a

A copy of the orbitals used in the CC reference calculation

e_ref

The total energy of the CC reference function

18.2.1. Summary of keyword arguments

The RSFCCD module supports various keyword arguments that allow us to steer the optimization of ionized states (ionization energies and the eigenvectors of the targeted states). In the following, all supported keyword arguments are listed together with their default values. Please note that for most cases, the default values should be sufficient to reach convergence.

nroot

(int) the number of targeted (ionized) states (default 1)

threshold

(float) printing threshold for the eigenvectors. If a (row) element of civ_ee is larger than the threshold in absolute value, the corresponding ionization contribution is printed (default 0.1)

tco

(str | None) the flavor of tensor contraction operations used. Either cupy, td or einsum (default None)

Note

PyBEST takes the most efficient tensor contraction operations for specific contractions. By default, selected operations are exported to the GPU using Cupy. If Cupy is not available, td is selected. einsum is taken if all other flavors are unsupported.

We do not recommend changing the default unless you know what you are doing. The tco keyword argument is deprecated.

dump_cache

(boolean) effective Hamiltonian elements are loaded and dumped to the disk whenever needed. Since large arrays are dumped to/read from disk, this implementation is slower but more memory-effective (default True if the number of active orbitals exceeds 300).

Some keyword arguments are working together with the Davidson solver:

tolerance

(float) optimization threshold for each ionization energy (default 1e-6)

tolerancev

(float) optimization threshold for each ionized state eigenvector (default 1e-4)

maxiter

(int) maximum number of total Davidson diagonalization steps (default 200)

nguessv

(int) total number of guess vectors (default (nroots-1)*4+1, that is, 4 vectors per ionized state)

maxvectors

(int) maximum number of Davidson vectors. If additional vectors are added, a subspace collapse is performed (default (nroots-1)*10, that is, 10 vectors per excited state)

todisk

(boolean) if set to True, all intermediates are stored to disk. This reduces memory requirements. However, due to the intensive I/O operations, the code is slowed down significantly (default False).