  We discus existent conflicts between experimentally measured and
theoretically calculated melting curves of Mo, Ta, and W. By assuming that
vacancy formation plays a fundamental role in the melting process, an
explanation for the measured melting curves is provided. Furthermore, we show
that the Lindemann law fits well all the measured melting curves of bcc
transition metals if the Grueneisen parameter is written as a power series of
the interatomic distance. For completeness, we examine possible reasons for
current disagreements between shock-wave and DAC experiments. To solve them, we
propose the existence of an extra high P-T phase for Mo, Ta, and W
