Print all parameters used in the calculation, the one-electron matrix, and two electron integrals .  This keyword should normally only be used with 1SCF, otherwise the output can be very large.

Two electron integrals are in the order: All integrals for atoms 1 with 1, 1 with 2, 2 with 2, 1 with 3, 2 with 3, 3 with 3, etc.  Within an atom-pair, the integrals are, in order:

<ss|ss> <ss|sx> <ss|xx> <ss|sy> <ss|xy> <ss|yy> ... <sx|ss> ... <(xy)(xy)|(xy)(xy)>

Atomic orbitals are, in order: s x y z (x2-y2) (xz) (z2) (yz) (xy)

The number of two-electron integrals can be quite large; for two atoms with d-orbitals (l = 2)  there are 2025  = 452 = ((9*10)/2)2 = ((l + 1)2*((l + 1)2 + 1)/2)2 distinct integrals.

HCORE is useful in diagnostic work - understanding how SCF methods work and in finding bugs in the program.