New features of BDF since 2020

The Beijing Density Functional (BDF) program package, with a history of over 30 years, is primarily characterized by its inclusion of the full range of relativistic Hamiltonians (one-, two-, quasi-four-, effective-four-, and four-component, as well as quantum electrodynamics) alongside fully symmetry-adapted density functional theory (DFT), time-dependent (TD) DFT, and single/multi-reference wave function theories (WFTs) for electronic structures and response properties of molecular systems. New features of BDF since its last summary [Zhang et al., J. Chem. Phys. 152, 064113 (2020)] include approximate treatments of relativistic effects, improved SCF solvers, implicit and explicit solvation models, enhanced TDDFT, new multi-reference WFT for strong correlation, and analytic gradients, Hessians, and nonadiabatic coupling matrix elements for both ground and excited states, as well as extensions to various spectroscopies. These developments have transformed BDF into a comprehensive and efficient electronic structure program well-suited for real-world applications.