  Some typical overlap/potential energy integrals which occur in the use of
extended Hylleraas-configuration interaction (E-Hy-CI) functions with
Slater-type orbital (STO) basis for two-electron atomic structure calculations,
have been evaluated analytically. The corresponding kinetic energy integrals
have been simplified first by using formulas derived from Gauss' divergence
theorem in vector calculus, and then expressed in terms of overlap / potential
energy matrix elements. Also closed-form expressions for such integrals which
arise in the application of Hylleraas-CI functions, and CI functions have been
obtained as special cases, and the calculated values are found to agree well
with correct results published by other investigators.
