  A model of localized electron wave packets (WPs) with variable position and
width (floating and breathing) that are spin-coupled as per the valence-bond
theory is presented. It produces accurate potential energy curves of LiH in the
ground singlet and triplet states. Quantization in a mean-field approximation
of the motion of a WP that corresponds to the Li 2s electron generates
semi-quantitative potential energy curves of low energy excited states.
Real-time semiquantal dynamics of the WP induced by an intense laser pulse
gives high-harmonic generation spectra that capture qualitative features of a
higher-level wave function calculation.
