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Disc space requirements:

In difference to CC2 and MP2, the CCSD model does no longer allow to avoid the storage of double excitation amplitudes (taibj) and intermediates of with a similar size. Thus, also the disc space requirements for the CCSD calculation are larger than for RI-MP2 and RI-CC2 calculation for the same system. For a (closed-shell) CCSD ground state energy calculations the amount of disc space needed can be estimated roughly as

Ndisk $\displaystyle \approx$ $\displaystyle \Big($4N3 + (4 + mDIIS)O2N2$\displaystyle \Big)$/(128×1024) MBytes , (10.18)

where N is the number of basis functions, O the number of occupied orbitals and mDIIS the number of vectors used in the DIIS procedure (by default 10, see Sec. 17.2.13 for details).

For (closed-shell) CCSD(T) calculations the required disc space is with

Ndisk $\displaystyle \approx$ $\displaystyle \Big($5N3 +5O2N2 + ON3$\displaystyle \Big)$/(128×1024) MBytes , (10.19)

somewhat larger.

For calculations with an open-shell (UHF or ROHF) reference wavefunctions the above estimates should be multiplied by factor of 4.


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Next: Memory requirements: Up: Characteristics of the Implementation Previous: Integral-direct implementation and resolution-of-the-identity   Contents   Index
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