For the He wave function, use

with Z_eff = 2 - 5/16, as obtained by the variational method. The measured value of the diamagnetic susceptibility is 1.88 x 10^-6 cm³/mole.

Using the Hamiltonian for an atomic electron in a magnetic field, determine, for a state of zero angular momentum, the energy, change to order B² if the system is in a uniform magnetic field represented by the vector potential A = 1/2B x r.

Defining the atomic diamagnetic susceptibility x by E = -1/2X B², calculate x for a helium atom in the ground state and compare the result with the measured value.

(X1, X2) = (Zeff/a)exp - Zerr(r+r2) ao