报告摘要 | The accuracy and computational efficiency of the widely used Kohn-Sham density functional theory (DFT) are limited by the approximation to its exchange-correlation energy Exc. The earliest local density approximation (LDA) overestimates the strengths of all bonds near equilibrium (even the vdW bonds). By adding the electron density gradient to model Exc, generalized gradient approximations (GGAs) generally soften the bonds to give robust and overall more accurate descriptions, except for the vdW interaction which is largely lost. Further improvement for covalent, ionic, and hydrogen bonds can be obtained by the computationally more expensive hybrid GGAs, which mix GGAs with the nonlocal exact exchange. Meta-GGAs are still semilocal in computation and thus efficient. Compared to GGAs, they add the kinetic energy density that enables them to recognize and accordingly treat different bonds, which no LDA or GGA can [2]. In this talk, I will present an advance in DFT, the recently developed non-empirical strongly constrained and appropriately normed (SCAN) meta-GGA [1]. SCAN predicts accurate geometries and energies of diversely-bonded molecules and materials (including covalent, metallic, ionic, hydrogen, and van der Waals bonds), significantly improving over its predecessors, the GGAs that dominate materials computation, at comparable efficiency [2]. SCAN’s excellent performance on cuprates, traditionally regarded as strongly-correlated systems out of reach of DFT, will be highlighted [3, 4]. For example, without invoking the Hubbard U, SCAN predicts landscapes of competing stripe and magnetic phases in YBa_{2}Cu_{3}O_{6} and YBa_{2}Cu_{3}O_{7} as archetype cuprate compounds [4]. In the latter material, we find many stripe phases that are nearly dgenerate with the ground state and may give rise to the pseudogap state from which the high-temperature superconducting state emerges. Lattice degrees of freedom are found to be crucially important in stabilizing the various phases. I will further explain how SCAN was constructed [1], why it can improve over GGAs [2], and where it should fail [5]. At the end, efforts to improve SCAN via nonlocal corrections will be discussed. References: [1] J. Sun, A. Ruzsinszky, and J.P. Perdew, Strongly constrained and appropriately normed semilocal density functional, *PRL ***115**, 036402 (2015). [2] J. Sun, R.C. Remsing, Y. Zhang, Z. Sun, A. Ruzsinszky, H. Peng, Z. Yang, A. Paul, U. Waghmare, X. Wu, M.L. Klein, and J.P. Perdew, Accurate first-principles structures and energies of diversely-bonded systems from an efficient density functional, *Nat. Chem.***8**, 831 (2016). [3] J.W. Furness, Y. Zhang, C. Lane, I.G. Buda, B. Barbiellini, R.S. Markiewicz, A. Bansil, and J. Sun, An accurate first-principles treatment of doping-dependent electronic structure of high-temperature cuprate superconductors, *Nature Communication Physics*, **1**, 11 (2018). [4] Y. Zhang, C. Lane, J.W. Furness, B. Barbiellini, R.S. Markiewicz, A. Bansil, and J. Sun, Landscape of competing stripe and magnetic phases in cuprates, arXiv: 1809.08457. [5] H. Peng, Z. Yang, J.P. Perdew, and J. Sun, Versatile van der Waals density functional based on a meta-generalized gradient approximation, *PRX ***6**, 041005 (2016). |