172 research outputs found
Comparing first-principles density functionals plus corrections for the lattice dynamics of YBaCuO
The enigmatic mechanism underlying unconventional high-temperature
superconductivity, especially the role of lattice dynamics, has remained a
subject of debate. Theoretical insights have long been hindered due to the lack
of an accurate first-principles description of the lattice dynamics of
cuprates. Recently, using the r2SCAN meta-GGA functional, we were able to
achieve accurate phonon spectra of an insulating cuprate YBaCuO,
and discover significant magnetoelastic coupling in experimentally interesting
Cu-O bond stretching optical modes [Phys. Rev. B 107, 045126 (2023)]. We extend
this work by comparing PBE and r2SCAN performances with corrections from the
on-site Hubbard U and the D4 van der Waals (vdW) methods, aiming at further
understanding on both the materials science side and the density functional
side. We demonstrate the importance of vdW and self-interaction corrections for
accurate first-principles YBa2 Cu3 O6 lattice dynamics. Since r2SCAN by itself
partially accounts for these effects, the good performance of r2SCAN is now
more fully explained. In addition, the performances of the Tao-Mo series of
meta-GGAs, which are constructed in a different way from SCAN/r2SCAN, are also
compared and discussed.Comment: arXiv admin note: text overlap with arXiv:2210.0656
Understanding the Quantum Oscillation Spectrum of Heavy-fermion Compound SmB6
SmB6 is a mysterious compound that is electrically insulating but yet it
exhibits quantum oscillations, which are a telltale signature of the metallic
state. Adding to the enigma is the possibility that SmB6 is a topological Kondo
insulator. Here, we report first-principles, parameter-free all-electron
electronic-structure calculations on SmB6, which yield the band structure and
crystal-field splittings within the f-electron complex in accord with
experiments. Predicted energies of several magnetic phases where charge, spin
and lattice degrees of freedom are treated on an equal footing are found to be
extremely close, indicating the key role of spin fluctuations in SmB6. Our
results show that the topological Kondo state of SmB6 is robust regardless of
its magnetic configuration. The Fermi surfaces derived from our predicted
ground state explain the experimentally observed bulk quantum oscillations, and
our large calculated effective mass of electrons at the Fermi surface explains
how the material is essentially insulating, with a measured specific heat that
is in excellent agreement with our calculations.Comment: 17 pages, 7 figures and 1 tabl
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