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CCSD(T) energy with a second-order correction from the interference-corrected MP2-F12:

The error introduced from a CCSD(T) calculation with a finite basis set can be corrected from second-order corrections of the the interference-corrected MP2-F12 (INT-MP2-F12) (Ref. [132]). The approximate CCSD(T)-INT-F12 at the basis set limit is given from

ECCSD(T)/CBS $\displaystyle \approx$ ECCSD(T) + $\displaystyle \sum_{{i<j}}^{}$Fij[eijMP2-F12 - eijMP2] . (10.26)

From define, in the submenu $ricc2 select the ccsd(t) method and add the keyword intcorr
$ricc2
  ccsd(t)
  intcorr
Then, switch on the f12 method (approximation A or B, inv or fixed). The corrected CCSD(T)-INT-F12 energy will be printed in the end of the calculation. It is highly recommended to start the CCSD(T)-INT-F12 calculation from a converged SCF calculation with symmetry, which is transfromed to C1 . It is furthermore recommended to use Boys localized orbitals in the $rir12 submenu. A table with the corrected second-order pair-electron energies and the corresponding interference factors can also be printed in the output by using the keyword intcorr all instead of intcorr.


next up previous contents index
Next: Excitation energies with CCSD: Up: Characteristics of the Implementation Previous: Important options:   Contents   Index
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