  The neutron rich isotopes with Z<20, in particular those with neutron numbers
around N=28,have been at the focus of a lot experimental and theoretical
scrutiny during the last few years.Shell model calculations using the effective
interaction SDPF-NR, were able to predictor to explain most of the properties
featured by these nuclei. Prominent among them is the disappearance of the N=28
shell closure for Z<=16. We have incorporated to SDPF-NR some modifications,
either on purely theoretical grounds or guided by new experimental information.
The proposed interaction, SDPF-U, contains USD as its sd-shell part and KB3G as
its pf-shell-part. Its range of applicability is enlarged and its reliability
enhanced with respect to the earlier version.
