  We have developed the capability to determine accurate harmonic spectra for
multielectron atoms within time-dependent R-matrix (TDRM) theory. Harmonic
spectra can be calculated using the expectation value of the dipole length,
velocity or acceleration operator. We assess the calculation of the harmonic
spectrum from He irradiated by 390 nm laser light with intensities up to 4 x
10(14) W cm(-2) using each form, including the influence of the multielectron
basis used in the TDRM code. The spectra are consistent between the different
forms, although the dipole acceleration calculation breaks down at lower
harmonics. The results obtained from TDRM theory are compared with results from
the HELIUM code finding good quantitative agreement between the methods. We
find that bases which include pseudostates give the best comparison with the
HELIUM code, but models comprising only physical orbitals also produce accurate
results.
