  To elucidate a novel pressure-temperature phase diagram of the
quasi-one-dimensional mixed-stack charge-transfer (CT) complex TTF-CA, we study
the quasi-one-dimensional spin-1 Blume-Emery-Griffith (BEG) model. In addition
to the local charge transfer energy and the inter-stack polar (dipole-dipole)
interaction, we take account of the inter-stack electrostriction effect. Using
the self-consistent chain-mean-field theory, where the intra-stack degrees of
freedom are exactly treated by the transfer-matrix method, we reproduce the
gas-liquid-solid like phase diagram corresponding to the neutral (N),
paraelectric ionic (I$_{\rm{para}}$), and ferroelectric ionic
(I$_{\rm{ferro}}$) phases, respectively. We also give an explanation on the
experimentally observed multicritical behavior and concomitant discontinuous
inter-stack lattice contraction in TTF-CA.
