Domain boundaries in Luttinger-Tisza ordered dipole lattices

Abstract

Motivated by the recent interest in the possible ordering of the CH3NH3 dipoles in the material CH3NH3PbI3, we investigate the properties of domain boundaries in a simple cubic lattice of dipoles. We perform numerical simulations in which we set the boundary conditions such that the dipoles at opposite sides of the simulated sample are ordered in different directions, hence simulating a domain boundary. We calculate the lowest energy configuration under this constraint. We find that if we consider only dipole-dipole interactions the dipole orientations tend to gradually transform between the two orientations at the two opposite ends of the sample. When we take into consideration the finite spatial size of the CH3NH3 molecules and go beyond the point dipole approximation, we find that the domain boundary becomes sharper. For the parameters of CH3NH3PbI3, our results indicate that the optimal energy structure has a boundary region of a width on the order of a single unit cell.

Long-range order imposed by short-range interactions in methylammonium lead iodide: Comparing point-dipole models to machine-learning force fields

“…Several model Hamiltonians describing the interactions of MA dipoles on a grid have been proposed in the last five years 24,[26][27][28][29][30][31][32][33] . In these models an effective Hamiltonian splits the total interaction energy of all N molecules in the cell in a short-range framework-dipole interaction and a long-range dipole-dipole interaction: H = H sr + H lr .…”

“…However, the length and time scales required to model the finite temperature structure occurring in real devices exclude a straightforward application of FPMD methods. Therefore effective model Hamiltonians that describe the potential energy surface of MA molecules on a lattice could be of great help in understanding the local structure at defects 23 and domain boundaries 24 . The presence of the reorienting molecules makes it difficult to apply models used for other perovskites, like BaTiO 3 25 .…”

“…The presence of the reorienting molecules makes it difficult to apply models used for other perovskites, like BaTiO 3 25 . Therefore point-dipole (pd) based model Hamiltonians 24,[26][27][28][29][30][31][32][33] , a rigid rotor cluster expansion 34 and classical force fields 35,36 have been designed. Often pd-models have been constructed in such a way that the heat capacity as function of temperature and/or phase transitions resemble experimental data.…”

Self-assembly of Pseudo-Dipolar Nanoparticles at Low Densities and Strong Coupling

“…The latter has the form f i (r) = −∇ U and is computed considering a cut-off distance equal to 4σ. The use of a spherical cut-off on dipolar interactions is a common assumption in coarse grained models that does not strongly affect the physics of the model system 16,17,21,[33][34][35] within the studied range of parameters. The last term in Eq.…”

Order in the ground state of a simple cubic dipole lattice in an external field

“…[9] More recently, spin models have been used to explore the long-range order in perovskites [10] and the structure of the interface between domains with different ordering patterns across the interface. [11] Spin models apply more generally to other systems in nature, some examples being the ordering of the electric dipoles of water molecules in ice [12] and the dipolar ordering of small molecules trapped in regular cage structures. [13][14][15] Artificially fabricated magnetic superstructures can also…”