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\title{Calculation of Multicenter Electron Repulsion
Integrals in Slater-Type Basis Sets Using the $\Sigma$ -
Separation Method}

\author{I.V. Maslov$^*$, H.H.H. Homeier and E.O. Steinborn\\[20pt]
{\normalsize Institut f\"ur Physikalische und Theoretische Chemie,}
 {\normalsize Universit\"at }\\
{\normalsize Regensburg, D-93040 Regensburg (Germany)}\\[40pt]
{\normalsize $^*$Permanent address: Laboratory of Molecular
Spectroscopy and }\\
{\normalsize Quantum Chemistry, V.I.Vernadsky
Institute of Geo- and Analytical}\\
{\normalsize Chemistry, Russian
Academy of Sciences, Kosygin Street 19,} \\
{\normalsize 117975 Moscow (Russian Federation)}}

\date{}

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Key words: multicenter molecular integrals, Slater-type
functions, $\Sigma$-separation method, numerical tests.

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{\Large \bf Abstract}

The application of the $\Sigma$-separation method to the calculation
of multicenter two-electron molecular integrals  with Slater-type
basis functions is reported. The approach is based on the
approximation of a scalar component of the two-center atomic density
by a two-center expansion over Slater-type functions. A least-squares
fit was used to determine the coefficients of the expansion. The
angular multipliers of the atomic density were treated exactly.

It is shown that this approach can serve as a sufficiently accurate
and fast algorithm for the calculation of multicenter two-electron
molecular integrals with Slater-type basis functions.

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