Inspired by biological systems that have the inherent skill to generate considerable bioelectricity from the salt content in fluids with highly selective ion channels and pumps on cell membranes, herein, a fully abiotic single‐pore nanofluidic energy‐harvesting system that efficiently converts Gibbs free energy in the form of a salinity gradient into electricity is demonstrated. The maximum power output with the individual nanopore approaches ∼26 pW. By exploiting parallelization, the estimated power density can be enhanced by one to three orders over previous ion‐exchange membranes. A theoretical description is proposed to explain the power generation with the salinity‐gradient‐driven nanofluidic system. Calculation results suggest that the electric‐power generation and its efficiency can be further optimized by enhancing the surface‐charge density (up to 100 mC m−2) and adopting the appropriate nanopore size (between 10 and 50 nm). This facile and cost‐efficient energy‐harvesting system has the potential to power biomedical tiny devices or construct future clean‐energy recovery plants.

Orbital-free density functional theory (OFDFT), with its attractive linearly scaling computation cost and low prefactor, is one of the most powerful first principles methods for simulating large systems (~10(4)-10(6) atoms). However, approximating the electron kinetic energy with density functionals limits the accuracy and generality of OFDFT compared to Kohn-Sham density functional theory (KSDFT). In this work, we test whether the Huang-Carter (HC) kinetic energy density functional (KEDF), which contains the physics to properly describe covalently bonded semiconductor materials, can also be used to describe covalent bonds in molecules. In particular, we calculate a variety of homonuclear diatomic molecules with the HC functional within OFDFT. The OFDFT bond dissociation energy, equilibrium bond length, and vibrational frequency of these dimers are in remarkably good agreement with benchmark KSDFT results, given the lack of orbitals in the calculation. We vary the two parameters λ (controlling the reduced density gradient contribution to the nonlocal kernel) and β (the exponent of the density in the nonlocal term) present in the HC KEDF and find that the optimal λ correlates with the magnitude of the highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap. Although the HC KEDF represents a significant improvement over previous KEDFs in describing covalent systems, deficiencies still exist. Despite the similar overall shape of the KSDFT and OFDFT ground state electron densities, the electron density within the bonding region is still quite different. Furthermore, OFDFT is not yet able to give reasonable description of magnetic states. The energy orderings of the triplet and singlet states of Si(2) and Al family dimers are not consistent with KSDFT or experimental results and the spin polarization distributions also differ widely between the two theories.

Molecular dynamics simulations of mixtures of 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM+][PF6-]) and water have been performed in order to investigate how small amounts of water affect the translational and rotational dynamics of this ionic liquid (IL). We find that water is closely associated with the anions and that its presence enhances both the translational and rotational dynamics of the IL. In agreement with experiments, we find that the fluorescence spectra of Coumarin-153 is red-shifted because of the presence of water. Small amounts of water enhance the speed of relaxation of the solvent surrounding the solute probe after photoexcitation, but only at a "local environment" level. Interconversion between environments still occurs on a long time scale compared with the fluorescence lifetime of the probe. Excitation wavelength-dependent emission is observed both in the neat IL and in the IL+water mixture.

We present a comprehensive study of single-point kinetic energy density functionals (KEDFs) to be used in orbital-free density functional theory (DFT) calculations. We first propose a new form of KEDFs based on a pointwise Kohn-Sham (KS) kinetic energy density (KED) and electron localization function (ELF) analysis. We find that the ELF and modified enhancement factor have a very strong and transferable correlation with the reduced density in various bulk metals. The non-self-consistent kinetic energy errors predicted by these new KEDF models are decreased greatly compared to previously-reported generalized gradient approximation (GGA) KEDFs.Second, we perform self-consistent calculations with various single-point KEDFs and investigate their numerical convergence behavior. We find striking numerical instabilities for previous GGA KEDFs; most of the GGA KEDFs fail to converge and show unphysical densities during the optimization. In contrast, our new KEDFs demonstrate stable convergence, and their self-consistent results of various bulk 2 properties agree reasonably well with KSDFT. A further detailed KED analysis reveals an interesting bifurcation phenomenon in defective metals and alloys, which may shed light on directions for future KEDF development.

238 wileyonlinelibrary.com COMMUNICATION available highly purifi ed CNTs, with reported purity of up to 99.9% or even higher. [ 22 ] Another factor leads to the slow progress on the development of high-performance CNT IR detectors is that device structure and operation mode have not been optimized for solution-processed CNTs to achieve performance comparable with that of state-of-the-art commercial IR detectors. [ 23,24 ] In this letter, we show that high-performance photodiodes can be constructed using solution-processed CNTs via a dopingfree technique. In contrast to other photodetectors that use photocurrent as the signal, [ 8,[11][12][13][14][15][16][17][18][19][20] here we exploit using photovoltage as the signal. The major benefi t of using photovoltage is that the commonly occurring shot noise and 1/ f noise can be signifi cantly suppressed. In addition, signal can be multiplied via introducing virtual contacts, which leads to further improvement on signal-to-noise ratio. A prototype CNT IR detector is demonstrated, which works at room temperature and shows broadband response, high responsivity and detectivity that are comparable to that of state-of-the-art room temperature semiconductor IR detectors. It is also demonstrated that our CNT IR detectors have excellent stability, as a result of the dopingfabrication process used here, with time, under high power illumination and at rigorous temperature conditions. An array of 150 × 150 photodetectors on a single chip is fabricated, with tested yield of 100% and high device uniformity, showing the potential for large-scale fabrication capability and imager applications.In a typical photovoltaic device, a built-in fi eld is essential for the effi cient separation of photoinduced electron-hole pairs. For CNT-based diodes, ideal rectifi cation behavior has been realized by using split gates or asymmetric contacts on individual CNTs. [ 9,10,13 ] However, light absorption in these devices is usually very weak. It is thus advantageous to construct a photodiode using CNT fi lm with more CNTs in the device channel. However, solution-processed CNT-fi lm-based diodes showing excellent rectifi cation effect have not been realized. [ 23,24 ] Here, we show that such high-performance diode based on solutionprocessed CNT fi lm can be realized by using a doping-free technique in a barrier-free-bipolar diode (BFBD) device geometry as depicted in Figure 1 a. In this device geometry, Sc and Pd are asymmetrically contacted to a CNT fi lm made by a liquidphase deposition technique on an n + silicon/SiO 2 substrate (see Figure S1a,b, Supporting Information). Thus, p-region and n-region are automatically formed adjacent to the contacts by charge transfer from the contacts. This process involves no intentionally introduced dopants, no extra defects on CNTs,

We propose a density decomposition scheme using a Wang-Govind-Carter (WGC)-based kinetic energy density functional (KEDF) to accurately and efficiently simulate various covalently bonded molecules and materials within orbital free (OF) density functional theory (DFT). By using a local, density-dependent scale function, the total density is decomposed into a highly localized density within covalent bond regions and a flattened delocalized density, with the former described by semilocal KEDFs and the latter treated by the WGC KEDF. The new model predicts reasonable equilibrium volumes, bulk moduli, and phase ordering energies for various semiconductors compared to Kohn-Sham (KS) DFT benchmarks. The decomposition formalism greatly improves numerical stability and accuracy while retaining computational speed compared to simply applying the original WGC KEDF to covalent materials. The surface energy of Si (100) and various diatomic molecule properties can be stably calculated and also agree well with KSDFT benchmarks. This linear scaling, computationally efficient, density-partitioned/multi-KEDF scheme opens the door to large scale simulations of molecules, semiconductors, and insulators with OFDFT.2

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The Weighted Histogram Analysis Method (WHAM) and unbinned versions such as the Multistate Bennett Acceptance Ratio (MBAR) and Unbinned WHAM (UWHAM) are widely used to compute free energies and expectations from data generated by independent or coupled parallel simulations. Here we introduce a Replica Exchange-like algorithm (RE-SWHAM) that can be used to solve the UWHAM equations stochastically. This method is capable of analyzing large data sets generated by hundreds or even thousands of parallel simulations that are too large to be “WHAMMED” using standard methods. We illustrate the method by applying it to obtain free energy weights for each of the 240 states in a simulation of host-guest ligand binding containing ~ 3.5 × 107 data elements collected from 16 parallel Hamiltonian Replica Exchange simulations, performed at 15 temperatures. In addition to using much less memory, RE-SWHAM showed a nearly eighty fold improvement in computational time compared with UWHAM.