Applicability of conventional band theory and the role of phenons in high Tc superconductors

State-of-the-art electronic structure and total energy calculations within the local density approximation (LDA) describe many of the features of the high-Tc oxides, including transport properties, structures, and phonon frequencies. LDA, however, does not give sufficient exchange splitting to give a stable antiferromagnetic solution in La2CuO4, even when the symmetry is relaxed and the in-plane oxygens are allowed to spin polarize. Nevertheless, the accuracy of the predictions of paramagnetic calculations suggests that the spin fluctuations play only a minor role in determining transport and lattice dynamics in the superconducting samples