Electronic and magnetic properties of an organic multiferroic: (C2H5NH3)2CuCl4

(C2H5NH3)(2)CuCl4 was proposed to be a ferroelectric material with dominant ferromagnetic interactions. Using first-principles calculations we find that the insulating state and in-plane ferromagnetism induced by d(z2-x2)-d(z2-y2) orbital order can be expressed well by generalized gradient approximation (GGA) at ambient pressure. While the Jahn Teller distortion (JTD) is suppressed under critical pressure of 4 GPa, as a result the new d(z)z orbital order leads to in-plane antiferromagnetism. Meanwhile the conventional GGA gives a wrong metal state. Our results suggest that (C2H5NH3)(2)CuCl4 is a strong correlated charge transfer insulator, while the depress of JTD by pressure changes it to a Mott Hubbard insulator. (C) 2013 Elsevier B.V. All rights reserved.