Low-energy spectrum of iron-sulfur clusters directly from many-particle quantum mechanics

FeS clusters are a universal biological motif. They carry out electron transfer, redox chemistry, and even oxygen sensing, in diverse processes including nitrogen fixation, respiration, and photosynthesis. The low-lying electronic states are key to their remarkable reactivity, but cannot be directly observed. Here we present the first ever quantum calculation of the electronic levels of [2Fe-2S] and [4Fe-4S] clusters free from any model assumptions. Our results highlight limitations of long-standing models of their electronic structure. In particular, we demonstrate that the widely used Heisenberg-Double-Exchange model underestimates the number of states by 1-2 orders of magnitude, which can conclusively be traced to the absence of Fe d$\rightarrow$d excitations, thought to be important in these clusters. Further, the electronic energy levels of even the same spin are dense on the scale of vibrational fluctuations, and this provides a natural explanation for the ubiquity of these clusters in nature for catalyzing reactions.Comment: Nature Chemistry, 201

Project 150

The purpose of Project 150 is to serve homeless students with support and services to continue school throughout graduation.https://digitalscholarship.unlv.edu/educ_sys_202/1048/thumbnail.jp

Geometries of third-row transition-metal complexes from density-functional theory

A set of 41 metal-ligand bond distances in 25 third-row transition-metal complexes, for which precise structural data are known in the gas phase, is used to assess optimized and zero-point averaged geometries obtained from DFT computations with various exchange-correlation functionals and basis sets. For a given functional (except LSDA) Stuttgart-type quasi-relativistic effective core potentials and an all-electron scalar relativistic approach (ZORA) tend to produce very similar geometries. In contrast to the lighter congeners, LSDA affords reasonably accurate geometries of 5d-metal complexes, as it is among the functionals with the lowest mean and standard deviations from experiment. For this set the ranking of some other popular density functionals, ordered according to decreasing standard deviation, is BLYP > VSXC > BP86 approximate to BPW91 approximate to TPSS approximate to B3LYP approximate to PBE > TPSSh > B3PW91 approximate to B3P86 approximate to PBE hybrid. In this case hybrid functionals are superior to their nonhybrid variants. In addition, we have reinvestigated the previous test sets for 3d- (Buhl M.; Kabrede, H. J. Chem. Theory Comput. 2006, 2, 1282-1290) and 4d- (Waller, M. P.; Buhl, M. J. Comput. Chem. 2007,28,1531-1537) transition-metal complexes using all-electron scalar relativistic DFT calculations in addition to the published nonrelativistic and ECP results. For this combined test set comprising first-, second-, and third-row metal complexes, B3P86 and PBE hybrid are indicated to perform best. A remarkably consistent standard deviation of around 2 pm in metal-ligand bond distances is achieved over the entire set of d-block elements.PostprintPeer reviewe

The Role of Music in the Enhancement of Marketing

Marketers use thousands of techniques in order to create the ideal brand image for products and services. There is no detail left unconsidered at the end of a marketing proposal. Everything from the font on a package to the actor used in commercials is extremely thought-out because marketers are not trying to sell a product; they are trying to sell a brand. Because of this, music is becoming increasingly important in marketing decisions. The types of music playing in a store, on a commercial, on a website, or at a worksite can all effect the image of a product, and ultimately whether or not a product sells. This thesis will examine the correlation between marketing and music, and how markers can use music to help develop an effective brand. Music that is effectively utilized and implemented can greatly contribute to the branding and marketing effort of a company or product. Key Words: music in marketing, branding, memor

Comparison of Many-Particle Representations for Selected Configuration Interaction: II. Numerical Benchmark Calculations

The present work is the second part in our three-part series on the comparison of many-particle representations for the selected configuration interaction (CI) method. In this work, we present benchmark calculations based on our selected CI program called the iterative configuration expansion (ICE) that is inspired by the CIPSI method of Malrieu and co-workers (Malrieu J. Chem. Phys. 1973, 58, (12), 5745−5759). We describe the main parameters that enter in this algorithm and perform benchmark calculations on a set of 21 small molecules and compare ground state energies with full configuration interaction (FCI) results (FCI21 test set). The focus is the comparison of the performance of three different types of many-particle basis functions (MPBFs): (1) individual Slater determinants (DETS), (2) individual spin-adapted configuration state functions (CSFs), and (3) all CSFs of a given total spin that can be generated from spatial configurations (CFGs). An analysis of the cost of the calculation in terms of the number of wavefunction parameters and the energy error is evaluated for the DET-, CFG-, and CSF-based ICE. The main differences for the three many-particle basis representations show up in the number of wavefunction parameters and the rate of convergence toward the FCI limit with the thresholds of the ICE. Next, we analyze the best way to extrapolate the ICE energies toward the FCI results as a function of the thresholds. The efficiency of the extrapolation is investigated relative to the FCI21 test set as well as near FCI calculations on three moderately sized hydrocarbon molecules CH4, C2H4, and C4H6. Finally, we comment on the size-inconsistency error for the three many-particle representations and compare it with the error in the total energy. The implication for selected CI implementations with any of the three many-particle representations is discussed

Hybrid functional calculations of the Al impurity in silica: Hole localization and electron paramagnetic resonance parameters

We performed first-principle calculations based on the supercell and cluster approaches to investigate the neutral Al impurity in smoky quartz. Electron paramagnetic resonance measurements suggest that the oxygens around the Al center undergo a polaronic distortion which localizes the hole being on one of the four oxygen atoms. We find that the screened exchange hybrid functional successfully describes this localization and improves on standard local density approaches or on hybrid functionals that do not include enough exact exchange such as B3LYP. We find a defect level at about 2.5 eV above the valence band maximum, corresponding to a localized hole in a O 2p orbital. The calculated values of the g tensor and the hyperfine splittings are in excellent agreement with experiment.Comment: 5 pages, 2 figures, 1 tabl