next up previous contents index
Next: Prerequisites Up: DOK Previous: Comments on Output   Contents   Index

Second-Order Approximate Coupled-Cluster (CC2) Calculations

RI-CC2

ricc2 is a module for the calculation of excitation energies and response properties at a correlated ab initio level, in particular the second-order approximate coupled-cluster model CC2 [86]. All calculations employ the resolution-of-the-identity (RI) approximation for the electron repulsion integrals needed for the correlation treatment and and the description of excitation processes. At present the following functionalities are implemented:

ground state energies
for MP2 and CC2 and spin-component scaled variants thereof; the MP2 results are identical with those obtained with rimp2 (but usually the calculations are somewhat faster).
excitation energies
for the models CIS/CCS, CIS(D), CIS(D$ _\infty$), ADC(2), and CC2
transition moments
for ground state--excited and excited--excited state transitions for the models CCS and CC2
first-order properties
for the ground state (SCF/CCS, MP2, and CC2) and excited states (CCS, CC2, ADC(2) and CIS(D$ _\infty$))
geometric gradients
for the electronic ground state at the MP2 and the CC2 level; for electronically excited states at the CIS(D$ _\infty$), ADC(2), and CC2 level
gradients for auxiliary basis sets
for RI-MP2, -CC2, etc. calculations based on the RI-MP2 error functional
F12 corrections
to RI-MP2; MP2 ground-state energies can be computed (in $ C_1$ symmetry) using explicitly-correlated two-electron basis functions in the framework of the MP2-F12 model [87,88].
All functionalities are implemented for closed-shell RHF and open-shell UHF reference wavefunctions. Ground (MP2, CC2) and excited state energies (CC2, CIS(D$ _\infty$), ADC(2)) are also implemented for single determinant restricted open-shell reference wavefunctions.



Subsections
next up previous contents index
Next: Prerequisites Up: DOK Previous: Comments on Output   Contents   Index
TURBOMOLE