# CCHBAR¶

Assembles the coupled cluster effective Hamiltonian. Called whenever CC properties and/or gradients are required.

## General¶

### CACHELEVEL¶

Caching level for libdpd governing the storage of amplitudes, integrals, and intermediates in the CC procedure. A value of 0 retains no quantities in cache, while a level of 6 attempts to store all quantities in cache. For particularly large calculations, a value of 0 may help with certain types of memory problems. The default is 2, which means that all four-index quantities with up to two virtual-orbital indices (e.g., $$\langle ij | ab \rangle$$ integrals) may be held in the cache.

• Type: integer
• Default: 2

### EOM_REFERENCE¶

Reference wavefunction type for EOM computations

• Type: string
• Default: RHF

### T_AMPS¶

Do compute the T amplitude equation matrix elements?

### WABEI_LOWDISK¶

Do use the minimal-disk algorithm for Wabei? It’s VERY slow!

## Expert¶

### WFN¶

Wavefunction type

• Type: string
• Default: SCF