  We study the a, b and c coefficients of the isobaric-multiplet mass equation
using a macroscopic-microscopic approach developed by P. Moeller and his
collaborators in ADNDT 59, 185 (1995) and ADNDT 109-110, 1 (2016). We show that
already the macroscopic part of the finite-range liquid-drop model (FRLDM)
describes the general trend of the a and b coefficients relatively well, while
the staggering behavior of b coefficients for doublets and quartets can be
understood in terms of the difference of average proton and neutron pairing
energies. The sets of isobaric masses, predicted by the full
macroscopic-microscopic approaches, are used to explore the general trends of
IMME coefficients up to A=100. We conclude that while the agreement for a
coefficients is quite satisfactory, the global approaches have less sensitivity
to predict the staggering pattern observed for b coefficients of doublets and
quartets. The best set of theoretical b coefficients for multiplets up to about
A=100 is used to predict masses of proton-rich nuclei based on the known
experimental masses of neutron-rich mirror partners, and subsequently to
investigate their one- and two-proton separation energies. The estimated
position of the proton-drip line is in fair agreement with known experimental
data. These masses are important for simulations of the astrophysical
rp-process.
