1,819 research outputs found
Non-Empirically Tuned Range-Separated DFT Accurately Predicts Both Fundamental and Excitation Gaps in DNA and RNA Nucleobases
Using a non-empirically tuned range-separated DFT approach, we study both the
quasiparticle properties (HOMO-LUMO fundamental gaps) and excitation energies
of DNA and RNA nucleobases (adenine, thymine, cytosine, guanine, and uracil).
Our calculations demonstrate that a physically-motivated, first-principles
tuned DFT approach accurately reproduces results from both experimental
benchmarks and more computationally intensive techniques such as many-body GW
theory. Furthermore, in the same set of nucleobases, we show that the
non-empirical range-separated procedure also leads to significantly improved
results for excitation energies compared to conventional DFT methods. The
present results emphasize the importance of a non-empirically tuned
range-separation approach for accurately predicting both fundamental and
excitation gaps in DNA and RNA nucleobases.Comment: Accepted by the Journal of Chemical Theory and Computatio
PAMELA: An Open-Source Software Package for Calculating Nonlocal Exact Exchange Effects on Electron Gases in Core-Shell Nanowires
We present a new pseudospectral approach for incorporating many-body,
nonlocal exact exchange interactions to understand the formation of electron
gases in core-shell nanowires. Our approach is efficiently implemented in the
open-source software package PAMELA (Pseudospectral Analysis Method with
Exchange & Local Approximations) that can calculate electronic energies,
densities, wavefunctions, and band-bending diagrams within a self-consistent
Schrodinger-Poisson formalism. The implementation of both local and nonlocal
electronic effects using pseudospectral methods is key to PAMELA's efficiency,
resulting in significantly reduced computational effort compared to
finite-element methods. In contrast to the new nonlocal exchange formalism
implemented in this work, we find that the simple, conventional
Schrodinger-Poisson approaches commonly used in the literature (1) considerably
overestimate the number of occupied electron levels, (2) overdelocalize
electrons in nanowires, and (3) significantly underestimate the relative energy
separation between electronic subbands. In addition, we perform several
calculations in the high-doping regime that show a critical tunneling depth
exists in these nanosystems where tunneling from the core-shell interface to
the nanowire edge becomes the dominant mechanism of electron gas formation.
Finally, in order to present a general-purpose set of tools that both
experimentalists and theorists can easily use to predict electron gas formation
in core-shell nanowires, we document and provide our efficient and
user-friendly PAMELA source code that is freely available at
http://alum.mit.edu/www/usagiComment: Accepted by AIP Advance
The Diamine Cation Is Not a Chemical Example Where Density Functional Theory Fails
In a recent communication, Weber and co-workers presented a surprising study
on charge-localization effects in the N,N'-dimethylpiperazine (DMP+) diamine
cation to provide a stringent test of density functional theory (DFT) methods.
Within their study, the authors examined various DFT methods and concluded that
"all DFT functionals commonly used today, including hybrid functionals with
exact exchange, fail to predict a stable charge-localized state." This
surprising conclusion is based on the authors' use of a self-interaction
correction (namely, complex-valued Perdew-Zunger Self-Interaction Correction
(PZ-SIC)) to DFT, which appears to give excellent agreement with experiment and
other wavefunction-based benchmarks. Since the publication of this recent
communication, the same DMP+ molecule has been cited in numerous subsequent
studies as a prototypical example of the importance of self-interaction
corrections for accurately calculating other chemical systems. In this
correspondence, we have carried out new high-level CCSD(T) analyses on the DMP+
cation to show that DFT actually performs quite well for this system (in
contrast to their conclusion that all DFT functionals fail), whereas the PZ-SIC
approach used by Weber et al. is the outlier that is inconsistent with the
high-level CCSD(T) (coupled-cluster with single and double excitations and
perturbative triples) calculations. Our new findings and analysis for this
system are briefly discussed in this correspondence.Comment: Accepted by Nature Communication
Solid state lithiation-delithiation of sulphur in sub-nano confinement: a new concept for designing lithium-sulphur batteries.
We investigate the detailed effects and mechanisms of sub-nano confinement on lithium-sulfur (Li-S) electrochemical reactions in both ether-based and carbonate-based electrolytes. Our results demonstrate a clear correlation between the size of sulfur confinement and the resulting Li-S electrochemical mechanisms. In particular, when sulfur is confined within sub-nano pores, we observe identical lithium-sulfur electrochemical behavior, which is distinctly different from conventional Li-S reactions, in both ether and carbonate electrolytes. Taken together, our results highlight the critical importance of sub-nano confinement effects on controlling solid-state reactions in Li-S electrochemical systems
- …