|The effect of uniaxial strain on electronic structure and magnetism in LaMnO3 is studied from a
model Hamiltonian that illustrates the competition between the Jahn-Teller, super exchange, and
double exchange interactions. We retain in our model the three main octahedral distortions (Q1,Q2,
and Q3), which couple to the Mn (eg) electrons. Our results show the ground state to be a type
A antiferromagnetic (AFM) insulating state for the unstrained case, consistent with experiments.
With tensile strain (stretching along the c axis), the ground state changes into a ferromagnetic
and eventually into a type G0 AFM structure, while with compressive strain, we find the type A
switching into a type G structure. The orbital ordering, which displays the well known checkerboard
x2−1/y2−1 structure for the unstrained case, retains more or less the same character for compressive
strain, while changing into the z2 − 1 character for tensile strains. While Q1 and Q3 are fixed by
the strain components "xx and "zz in our model, the magnitude of the in-plane distortion mode
(Q2), which varies to minimize the total energy, slowly diminishes with tensile strain, completely
disappearing as the FM state is entered. Within our model, the FM state is metallic, while the
three AFM states are insulating.