Two-parameter wavefunction for the ground state of the helium isoelectronic sequence

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Abstract
A simple two-parameter wavefunction for the ground state of two-electron atoms has been obtained by introducing variational parameters in the Hamiltonian rather than in the trial wavefunction. The energy eigenvalues have been calculated for atoms with nuclear charge Z in the range I<or=Z<or=12. The binding energies so obtained are observed to be better than the corresponding one-parameter (only screening) values, and are in reasonable agreement with very accurate multiparameter results reported by earlier workers. The method proposed is only easily extendable to those configurations in which both the electrons occupy the same orbital.