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31 EXPLICITLY CORRELATED METHODS 233<br />

ccsd(t)-f12,ri basis=optri<br />

would be sufficient. Note, however, that without the specification OPTRI the avtz/jkfit basis set<br />

would be used for the RI. For example,<br />

basis=avtz<br />

hf<br />

ccsd(t)-f12<br />

is equivalent to<br />

basis=avtz<br />

hf<br />

ccsd(t)-f12,df_basis=avtz/mp2fit,df_basis_exch=vtz/jkfit,ri_basis=vtz/jkfit<br />

If the VnZ-F12 basis sets are used, the OPTRI sets are used by default, i.e.,<br />

basis=vtz-f12<br />

hf<br />

ccsd(t)-f12<br />

is equivalent to<br />

basis=vtz-f12<br />

hf<br />

ccsd(t)-f12,df_basis=avtz/mp2fit,df_basis_exch=vtz/jkfit,\\<br />

ri_basis=vtz-f12/optri<br />

31.5 Symmetry<br />

Symmetry cannot be used in DF-LMP2-F12 calculations. However, in MP2-F12, DF-MP2-<br />

F12, DF-RMP2-F12, CCSD(T)-F12 and UCCSD(T)-F12 calculations Abelian symmetry can<br />

be used as usual; in these cases the preceding DF-MP2-F12 calculations will be automatically<br />

performed without symmetry, and the integrals that are necessary for subsequent CCSD-F12<br />

or UCCSD-F12 calculations will be transformed to the symmetry adapted basis. This is fully<br />

automatic and transparent to the user. Note, however, that the prefix DF- turns off symmetry<br />

automatically, and if you want to use symmetry in the HF calculations preceding the DF-MP2-<br />

F12 or DF-MP2-F12 calculations the symmetry elements (or AUTO) must be specified using the<br />

SYMMETRY directive (setting SYMMETRY,AUTO works fine).<br />

31.6 Options<br />

There are many options available, but these are hardly needed. Normally, when standard orbital<br />

basis sets such as aug-cc-PVTZ or VTZ-F12 are used, appropriate defaults are used and no<br />

further options are needed. A typical input simply reads<br />

basis=vtz-f12<br />

hf<br />

ccsd(t)-f12

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