Niranjan V. Ilawe

Breaking Badly: DFT-D2 Gives Sizeable Errors for Tensile Strengths in Palladium-Hydride Solids

Dispersion interactions play a crucial role in noncovalently bound molecular systems, and recent studies have shown that dispersion effects are also critical for accurately describing covalently bound solids. While most studies on bulk solids have solely focused on equilibrium properties (lattice constants, bulk moduli, and cohesive energies), there has been little work on assessing the importance of dispersion effects for solid-state properties far from equilibrium. In this work, we present a detailed analysis of both equilibrium and highly nonequilibrium properties (tensile strengths leading to fracture) of various palladium-hydride systems using representative DFT methods within the LDA, GGA, DFT-D2, DFT-D3, and nonlocal vdw-DFT families. Among the various DFT methods, we surprisingly find that the empirically constructed DFT-D2 functional gives extremely anomalous and qualitatively incorrect results for tensile strengths in palladium-hydride bulk solids. We present a detailed analysis of these effects and discuss the ramifications of using these methods for predicting solid-state properties far from equilibrium. Most importantly, we suggest caution in using DFT-D2 (or other coarse-grained parametrizations obtained from DFT-D2) for computing material properties under large stress/strain loads or for evaluating solid-state properties under extreme structural conditions.

Polarizabilities of π-Conjugated Chains Revisited: Improved Results from Broken-Symmetry Range-Separated DFT and New CCSD(T) Benchmarks.

We present a detailed analysis of nonempirically tuned range-separated functionals, with both short- and long-range exchange, for calculating the static linear polarizability and second hyperpolarizabilities of various polydiacetylene (PDA) and polybutatriene (PBT) oligomers. Contrary to previous work on these systems, we find that the inclusion of some amount of short-range exchange does improve the accuracy of the computed polarizabilities and second hyperpolarizabilities. Most importantly, in contrast to prior studies on these oligomers, we find that the lowest-energy electronic states for PBT are not closed-shell singlets, and enhanced accuracy with range-separated DFT can be obtained by allowing the system to relax to a lower-energy broken-symmetry solution. Both the computed polarizabilities and second hyperpolarizabilities for PBT are significantly improved with these broken-symmetry solutions when compared to previously published and current benchmarks. In addition to these new analyses, we provide new large-scale CCSD(T) and explicitly correlated CCSD(T)-F12 benchmarks for the PDA and PBT systems, which comprise the most complete and accurate calculations of linear polarizabilities and second hyperpolarizabilities on these systems to date. These new CCSD(T) and CCSD(T)-F12 benchmarks confirm our DFT results and emphasize the importance of broken-symmetry effects when calculating polarizabilities and hyperpolarizabilties of π-conjugated chains.

Sultam-Based Hetero[5]helicene: Synthesis, Structure, and Crystallization-Induced Emission Enhancement

A deep-blue-emitting sultam-based hetero[5]helicene was synthesized in four steps, and its crystal structure and physical properties were characterized. The helicene displays more than two-fold crystallization-induced emission enhancement as well as atypical blue-shifting of its solid-state emission relative to the solution phase. This rapid synthesis of an unusual sulfonamide-based helicene fluorophore is expected to generate new molecular design options that will help address the ongoing challenges associated with designing pure-blue emitters for organic optoelectronic and sensing applications.

Effect of quantum tunneling on the efficiency of excitation energy transfer in plasmonic nanoparticle chain waveguides

We present a detailed analysis of the electronic couplings that mediate excitation energy transfer (EET) in plasmonic nanoantenna systems using large-scale quantum dynamical calculations. To capture the intricate electronic interactions in these large systems, we utilize a real-time, time-dependent, density functional tight binding (RT-TDDFTB) approach to characterize the quantum-mechanical efficiency of EET in plasmonic nanoparticle chains with subnanometer interparticle spacings. In contrast to classical electrodynamics methods, our quantum dynamical calculations do not predict a monotonic increase in EET efficiency with a decrease in interparticle spacing between the nanoparticles of the nanoantenna. Most notably, we show a sudden drop in EET efficiencies as the interparticle distance approaches subnanometer length scales within the nanoparticle chain. We attribute this drop in EET efficiency to the onset of quantum charge tunneling between the nanoparticles of the chain which, in turn, changes the nature of the electronic couplings between them. We further characterize this abrupt change in EET efficiency through visualizations of both the spatial and time-dependent charge distributions within the nanoantenna, which provide an intuitive classification of the various types of electronic excitations in these plasmonic systems. Finally, while the use of classical electrodynamics methods have long been used to characterize complex plasmonic systems, our findings demonstrate that quantum-mechanical effects can result in qualitatively different (and sometimes completely opposite) results that are essential for accurately calculating EET mechanisms and efficiencies in these systems.

Correction to Real-Time Quantum Dynamics of Long-Range Electronic Excitation Transfer in Plasmonic Nanoantennas

I the original version of the article, within the Theory and Methodology Section, the following sentences contain incorrect citations. The corrected references should be as follows: Page 3443: These matrix elements are pretabulated for all pairs of chemical elements, as a function of distance between atomic pairs, significantly improving the computational efficiency of the DFTB approach. Page 3443: The second term in eq 2 is the energy due to charge fluctuations and is parametrized analytically as a function of orbital charges and γAB, which is a function of interatomic separation and Hubbard parameter, U. Page 3443: These pairwise repulsive functions are obtained by fitting to DFT calculations using a suitable reference structure. Page 3444: This formalism has been previously used to probe the nonequilibrium electron dynamics in several large chemical systems, including photoinjection dynamics in dyesensitized TiO2 solar cells 4,5 and many-body interactions in solvated nanodroplets. Page 3444: When the applied incident fields are smaller than the internal fields within the matter, the system is found to be in the linear response regime. The new references (numbered 1−6) are included in this Erratum. References 37 and 43 are in the original manuscript. The authors apologize for these mistakes.