AB-INITIO CALCULATION OF SCATTERING LENGTH AND CROSS-SECTIONS AT VERY-LOW ENERGIES FOR ELECTRON-HELIUM SCATTERING

The multiconfiguration Hartree-Fock method for continuum wave function s has been used to calculate the scattering length and phase shifts ov er extremely low energies ranging from 0 to 1 eV very accurately for e lectron-helium scattering. The scattering length is calculated very ac curately with wave functions computed exactly at zero energy, resultin g in an upper bound of 1.1784. The electron correlation and polarizati on of the target by the scattering electron, which are very important in these calculations, have been taken into account in an accurate ab initio manner through the configuration-interaction procedure by optim izing both bound and continuum orbitals simultaneously at each kinetic energy of the scattered electron. Detailed results for scattering len gth, differential, total, and momentum-transfer cross sections obtaine d from the phase shifts are presented. The present scattering length i s found to be in excellent agreement with the experimental result of A ndrick and Bitsch [J. Phys. B 8, 402 (1975)] and the theoretical resul t of O'Malley, Burke, and Berrington [J. Phys. B 12, 953 (1979)]. Ther e is excellent agreement between the present total cross sections and the corresponding experimental measurements of Buckman and Lohmann [J. Phys. B 19, 2547 (1986)]. The present momentum-transfer cross section s also show remarkable agreement with the experimental results of Crom pton, Elford, and Robertson [Aust. J. Phys. 23, 667 (1970)].