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By the inclusion of half-integral powers in the Hylleraas functions for the ground state of the helium atom, it is possible to obtain more rapid convergence in the Ritz variational method applied to the nonrelativistic Schr\"odinger equation (for infinite nuclear mass), as shown by results of calculations involving from four to thirteen parameters. The energy obtained with 13 parameters, -2.903719 a.u., is the lowest so far published. The coefficients for the normalized wave functions are given.
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Herman Schwartz (1956) studied this question.
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