Helium atoms in a strong magnetic field studied with the Lagrange-mesh method

The helium atom in a strong magnetic field B less than or equal to 2.35 x 10(5) T is studied with the help of the Lagrange-mesh method, in the case of an infinitely heavy nucleus. An approximate variational calculation is performed with a basis formed by combining Wigner functions depending on Euler angles with Lagrange functions for the three internal degrees of freedom. The Lagrange functions are associated with a three-dimensional mesh in perimetric coordinates. The method is applied to the determination of the energies of the two lowest singlet and triplet helium states with a total orbital momentum projection M equal to zero and to the lowest singlet M = -1 state.