Predicting building energy consumption is essential for planning and managing energy systems. In recent times, numerous studies focus on load forecasting models dealing with a wide range of different ...methods. In addition to Artificial Neural Networks (ANN), especially Support Vector Machines (SVM) have been studied. Various research work showed the success and superiority of ANN and SVM for load predictions, where frequently, SVM outperformed ANN models. In this study, data-driven thermal load forecasting performance of ε-SVM Regression (ε-SVM-R) based on a Radial Basis Function (RBF) and a polynomial kernel is compared to the outcome of two Nonlinear Autoregressive Exogenous Recurrent Neural Networks (NARX RNN) of different depths. For demonstration, historical data from a non-residential district in Germany is used for training and testing to predict monthly loads. The evaluation of the resulting predictions show that NARX RNNs yields higher accuracy than (ε-SVM-R) models, in combination with comparable computational effort.
•NARX RNNs are very powerful for data-driven predicting tasks related to DHC systems.•NARX RNNs outperform SVM-R models in terms of data-driven thermal load predictions.•Deeper NARX RNNs are able to improve forecast results of a building's energy demand.•Single-layered NARX RNNs provide high forecast accuracy and low computational effort.
The recently commissioned Linac Coherent Light Source is an X-ray free-electron laser at the SLAC National Accelerator Laboratory. It produces coherent soft and hard X-rays with peak brightness ...nearly ten orders of magnitude beyond conventional synchrotron sources and a range of pulse durations from 500 to <10 fs (10-15 s). With these beam characteristics this light source is capable of imaging the structure and dynamics of matter at atomic size and timescales. The facility is now operating at X-ray wavelengths from 22 to 1.2 A and is presently delivering this high-brilliance beam to a growing array of scientific researchers. We describe the operation and performance of this new 'fourth-generation light source'.
An effective state specific (SS) model for the inclusion of solvent effects in time dependent density functional theory (TD-DFT) computations of excited electronic states has been developed and coded ...in the framework of the so-called polarizable continuum model (PCM). Different relaxation time regimes can be treated thus giving access to a number of different spectroscopic properties together with solvent relaxation energies of paramount relevance in electron transfer processes. SS and conventional linear response (LR) models have been compared for two benchmark systems (coumarin 153 and formaldehyde in different solvents) and in the limiting simple case of a dipolar solute embedded in a spherical cavity. The results point out the complementarity of LR and SS approaches and the advantages of the latter model especially for polar solvents. The favorable scaling properties of PCM-TD-DFT models in both SS and LR variants and their availability in effective quantum mechanical codes pave the route for the computation of reliable spectroscopic properties of large molecules of technological and/or biological interest in their natural environments.
A geometry optimization method using an energy-represented direct inversion in the iterative subspace algorithm, GEDIIS, is introduced and compared with another DIIS formulation (controlled GDIIS) ...and the quasi-Newton rational function optimization (RFO) method. A hybrid technique that uses different methods at various stages of convergence is presented. A set of test molecules is optimized using the hybrid, GEDIIS, controlled GDIIS, and RFO methods. The hybrid method presented in this paper results in smooth, well-behaved optimization processes. The optimization speed is the fastest among the methods considered.
A state specific (SS) model for the inclusion of solvent effects in time dependent density functional theory (TD-DFT) computations of emission energies has been developed and coded in the framework ...of the so called polarizable continuum model (PCM). The new model allows for a rigorous and effective treatment of dynamical solvent effects in the computation of fluorescence and phosphorescence spectra in solution, and it can be used for studying different relaxation time regimes. SS and conventional linear response (LR) models have been compared by computing the emission energies for different benchmark systems (formaldehyde in water and three coumarin derivatives in ethanol). Special attention is given to the influence of dynamical solvation effects on LR geometry optimizations in solution. The results on formaldehyde point out the complementarity of LR and SS approaches and the advantages of the latter model especially for polar solvents and/or weak transitions. The computed emission energies for coumarin derivatives are very close to their experimental counterparts, pointing out the importance of a proper treatment of nonequilibrium solvent effects on both the excited and the ground state energies. The availability of SS-PCM/TD-DFT models for the study of absorption and emission processes allows for a consistent treatment of a number of different spectroscopic properties in solution.
The application of density functional theory to heavy elements and magnetic materials requires the generalization of existing functionals to the case of noncollinear spins. This letter describes a ...new idea to achieve such a generalization which, unlike previous efforts in this direction, (i) affords a nonvanishing local magnetic torque, (ii) is invariant with respect to spin-rotations, (iii) is free from numerical instabilities in regions of small magnetization, and (iv) reduces to the proper collinear limit.
Large π-conjugated molecules, when in contact with a metal surface, usually retain a finite electronic gap and, in this sense, stay semiconducting. In some cases, however, the metallic character of ...the underlying substrate is seen to extend onto the first molecular layer. Here, we develop a chemical rationale for this intriguing phenomenon. In many reported instances, we find that the conjugation length of the organic semiconductors increases significantly through the bonding of specific substituents to the metal surface and through the concomitant rehybridization of the entire backbone structure. The molecules at the interface are thus converted into different chemical species with a strongly reduced electronic gap. This mechanism of surface-induced aromatic stabilization helps molecules to overcome competing phenomena that tend to keep the metal Fermi level between their frontier orbitals. Our findings aid in the design of stable precursors for metallic molecular monolayers, and thus enable new routes for the chemical engineering of metal surfaces.
X-ray free-electron lasers, with pulse durations ranging from a few to several hundred femtoseconds, are uniquely suited for studying atomic, molecular, chemical and biological systems. ...Characterizing the temporal profiles of these femtosecond X-ray pulses that vary from shot to shot is not only challenging but also important for data interpretation. Here we report the time-resolved measurements of X-ray free-electron lasers by using an X-band radiofrequency transverse deflector at the Linac Coherent Light Source. We demonstrate this method to be a simple, non-invasive technique with a large dynamic range for single-shot electron and X-ray temporal characterization. A resolution of less than 1 fs root mean square has been achieved for soft X-ray pulses. The lasing evolution along the undulator has been studied with the electron trapping being observed as the X-ray peak power approaches 100 GW.
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