32. Prof. John Perdew - Density Functionals, Symmetry Breaking, and Strong Correlation

Full title: More-Predictive Density Functionals, Symmetry Breaking, and Strong Correlation
Speaker: Prof. John Perdew (Departments of Physics and Chemistry, Temple University, US)

First part:
00:00 - Introduction
02:02 - Beginning of the talk
03:50 - Correlated Wavefunction Theory and DFT
16:38 - Accomplishments and Challenges of DFT
13:27 - Hohenberg-Kohn theorem
27:14 - The Kohn-Sham approach
40:46 - Summary for the introductory part

Q&A part 1:
42:43 - Q1: Ways to solve the many-body problem other than DFT?
44:54 - Q2: Kohn-Sham one-electron orbitals
46:30 - Q3: Predicting ground states through machine learning from DFT

Second part:
52:30 - More predictive density functions
54:49 - Construction of DFT approximations
1:00:45 - SCAN: Construction, successes and failures
1:14:59 - Symmetry breaking and strong correlations in DFT
1:28:57 - Spin symmetry breaking in singlet C2 molecule
1:37:11 - Conclusions (2nd)

Q&A part 2:
1:39:08 - Q4: Ab initio methods or DFT?
1:41:06 - Q5: Singlet C2
1:44:17 - Q6: Exact functionals
1:46:40 - Q7: Poles in TD-DFT
1:50:29 - Q8: Broken symmetry
1:51:24 - Q9: Double hybrids
1:54:26 - Q10: Get better metallic properties with SCAN
1:56:03 - Q11: Hydrogen bonds on a metal surface
1:58:32 - Q12: Superconductivity with DFT
2:00:39 - Q13: How DFT accuracy should be assessed?
2:02:22 - Q14: How should we compare DFT with experiments?
2:05:13 - Q15: What DFT accuracy are we pursuing?


https://www.electrochemicalcolloquium...

#theory #DFT #physics

Abstract:
A 30-minute prologue to the research talk discusses what density functional theory is, why it is so widely used, what it has accomplished, and what challenges it still faces. 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).
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[1] J. Sun, A. Ruzsinszky, and J.P. Perdew, Phys. Rev. Lett. 115, 036402 (2015)
[2] J.W. Furness, Y. Zhang, C. Lane, I.G. Buda, B. Barbiellini, R.S. Markiewicz, A. Bansil, and J. Sun, Commun. Phys. 1, 11 (2018)
[3] P.W. Anderson, Science 177, 393 (1972)
[4] J.P. Perdew, A. Ruzsinszky, J. Sun, N.K. Nepal, and A.D. Kaplan, Proc. Nat. Acad. Sci. USA 118, e2017850118 (2021)