We study within a mean field theory the interplay between superconductivity and antiferromagnetism in
compounds. The hydrostatic or chemical pressure induces first-order phase transitions between superconducting, antiferromagnetic and mixed states in which superconductivity and antiferromagnetism coexist. In this work, we compare the pressure effects in experiments and nesting quality according to our calculations. We describe the
κ-phase of the
organic conductors by a two-band model exhibiting nesting properties governed by the ratio
. When we apply pressure in these compounds, we modify the Fermi surface shape and consequently the strength of the antiferromagnetic fluctuations depending on the nesting properties. Our theoretical description seems to explain various experimental data, for which, to our best knowledge, no clear theoretical interpretation has been given so far.