HERMIT is the integral evaluation part of the code. In ordinary
calculations there is no need to think about integral evaluation, as
this will be automatically taken care of by the program. However,
HERMIT has an extensive set of atomic one- and two-electron
integrals ,
and some users may find it useful to generate explicit integrals using
HERMIT . This is for instance necessary if the RESPONSE program (dynamic
properties) is to be
used, as described in Chapter 
. Disc usage may also
be reduced by not calculating the
supermatrix , and this is also controlled in the
**INTEGRALS
input section.
It is worth noticing that the two-electron part of HERMIT is actually two integral programs. One -- HERMIT -- is general and invoked by default in sequential calculations as well as in calculations using generally contracted basis sets. The other, ERI, is a highly vectorized code with orientation towards integral distributions. This code will be invoked in direct calculations using segmented basis sets for totally-symmetric Fock matrices.
Input to integral evaluation is indicated by the keyword **INTEGRALS , and the section may be ended with *END OF or any keyword starting with two stars (like e.g. **WAVE FUNCTIONS ). The intermediate input is divided into two sections: one general input section describing what molecular integrals is to be evaluated, and then a set of modules controling the different parts of the calculation of undifferentiated atomic integrals and the (possible) formation of a supermatrix as defined in for instance [67].