Semiempirical model for calculating the lattice dynamics of the Jahn-Teller oxide La2CuO4

Elastic properties of La2CuO4under pressure

“…The critical pressure P SPT at which the SPT from the orthorhombic phase (space group D 18 2h ) to the tetragonal phase (space group D 17 4h ) must have taken place has not been achieved experimentally at low temperatures. According to our calculations [10], the value of the critical pressure P SPT for La 2 CuO 4 at T = 0 K is equal to 5 GPa.…”

“…Note that the Jahn-Teller energy contribution plays a very important role in the crystal structure formation of K 2 CuF 4 [9] which has the same layered perovskite structure as La 2 CuO 4 , discussed in this work. The Jahn-Teller energy contribution was also found to be important for the correct simulation of the structure and lattice dynamics of La 2 CuO 4 [10] and this term determined the difference in physical properties between La 2 CuO 4 and La 2 NiO 4 [11]. We think that taking into account the multi-body Jahn-Teller contribution to the crystal energy of La 2 CuO 4 is preferable from the physical point of view to describing the Jahn-Teller effect by including the anisotropic Cu 2+ -O 2− pair potential (see, for example, [12]) or by considering the scaled Cu 2+ -O 2− pair potential involving apical oxygen (see [5]) †.…”

“…The values of all of the constants (i.e. C ij , D ij , λ ij , k i , A ij , and B ij ) needed to simulate La 2 CuO 4 as well as the methods used to determine them are given in our previous paper [10], devoted to the calculation of the structural properties of La 2 CuO 4 under pressure.…”

“…We approximate the multi-body Jahn-Teller contribution to the crystal energy as in [13] by the sum of expressions for the lower branches of CuO 6 cluster adiabatic potentials:…”

“…where the index k numbers all of the copper ions in the unit cell and the symmetrized coordinates Q θ , Q characterize the e g distortion of the oxide octahedra around the copper ions (for more details, see [10]). Evaluation of the linear Jahn-Teller coupling constant V e for the CuO 6 cluster with the distance R(Cu-O) = 0.21 nm (the average Cu-O distance in La 2 CuO 4 ) with the aid of the method of [14] gives V e = −2.5 nN.…”