Kharkiv Quantum Seminar: 2024 April 2, 17:00 (EEST)

More-predictive density functionals, symmetry breaking, and strong correlation

John P. Perdew

 (Department of Physics and Engineering Physics,Tulane University, New Orleans, LA, USA)

Approximate density functionals constructed to satisfy known mathematical properties of the exact density functional for the exchange-correlation energy of a many-electron system can be predictive over a wide range of materials and molecules. The strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation [1] satisfies 17 exact constraints, and nicely describes some systems that were formerly thought to be beyond the reach of density functional theory, such as the cuprates [2]. Ground states that break the symmetry of a Coulomb-interacting Hamiltonian can be understood as dynamic density or spin-density fluctuations that drop to low or zero frequency [3,4] and so persist over long times. In many cases, symmetry breaking transforms the strong correlation in a symmetry-unbroken wavefunction into moderate correlation like that found in the uniform electron gas of high or valence-electron density (an “appropriate norm” for constraint-based approximations).