Dispersion Size-Consistency

A multivariate adiabatic connection (MAC) framework for describing dispersion interactions in a system consisting of non-overlapping monomers is presented. By constraining the density to the physical ground-state density of the supersystem, the MAC enables a rigorous separation of induction and dispersion effects. The exact dispersion energy is obtained from the zero-temperature fluctuation-dissipation theorem and partitioned into increments corresponding to the interaction energy gained when an additional monomer is added to a -monomer system. The total dispersion energy of an -monomer system is independent of any partitioning into subsystems. This statement of dispersion size consistency is shown to be an exact constraint. The resulting additive separability of the dispersion energy results from multiplicative separability of the generalized screening factor defined as the inverse generalized dielectric function. Many-body perturbation theory (MBPT) is found to violate dispersion size-consistency because perturbative approximations to the generalized screening factor are nonseparable; on the other hand, random phase approximation-type methods produce separable generalized screening factors and therefore preserve dispersion size-consistency. This result further explains the previously observed increase in relative errors of MBPT for dispersion interactions as the system size increases. Implications for electronic structure theory and applications to supramolecular materials and condensed matter are discussed.

Three-dimensional convective dissolution of carbon dioxide into brine

The sequestration of carbon dioxide (CO2) through storage into deep saline aquifers represents an indispensable support technology to achieve the zero-carbon target necessary to mitigate the impact of CO2 on climate change. The effectiveness of the sequestration process, partly driven by the convective dissolution of CO2 in brine, is nowadays well characterized for two-dimensional geometries, low permeabilities, and small pressures of injection of CO2. However, reliable predictions of process-efficiency are missing because of the lack of full understanding of the three-dimensional (3D) spatio-temporal behaviour of CO2-rich convective fingers in brine over a large range of injection pressures. Here, we show that the convective dissolution is determined by the instability of the boundary layer formed at the interface between the two phases and is totally independent of the overall vertical size. Experiments were conducted over a broad range of injection pressures, close to process-relevant conditions. The results show the formation of complex 3D structures, including interconnecting stream tubes at the CO2-liquid interface, which could not be detected in previous 2D Hele-Shaw studies, and fingerings. A scale-free theoretical modelling of the convective process allows us to remap our laboratory results to length-scales of relevance for geological reservoirs. The experiments and the model show that the times needed for the onset of convection and the convective flux are independent of the system size.

Quantum harmonic free energies for biomolecules and nanomaterials

Obtaining the free energy of large molecules from quantum mechanical energy functions is a longstanding challenge. We describe a method that allows us to estimate, at the quantum mechanical level, the harmonic contributions to the thermodynamics of molecular systems of unprecedented size, with modest cost. Using this approach, we compute the vibrational thermodynamics of a series of diamond nanocrystals, and show that the error per atom decreases with system size in the limit of large systems. We further show that we can obtain the vibrational contributions to the binding free energies of prototypical protein-ligand complexes where the exact computation is too expensive to be practical. Our work raises the possibility of routine quantum mechanical estimates of thermodynamic quantities in complex systems.

On-site solar powered refueling stations for green hydrogen production and distribution: performances and costs

Today, the hydrogen is considered an essential element in speeding up the energy transition and generate important environmental benefits. Not all hydrogen is the same, though. The “green hydrogen”, which is produced using renewable energy and electrolysis to split water, is really and completely sustainable for stationary and mobile applications. This paper is focused on the techno-economic analysis of an on-site hydrogen refueling station (HRS) in which the green hydrogen production is assured by a PV plant that supplies electricity to an alkaline electrolyzer. The hydrogen is stored in low pressure tanks (200 bar) and then is compressed at 900 bar for refueling FCHVs by using the innovative technology of the ionic compressor. From technical point of view, the components of the HRS have been sized for assuring a maximum capacity of 450 kg/day. In particular, the PV plant (installed in the south of Italy) has a size of 8MWp and supplies an alkaline electrolyzer of 2.1 MW. A Li-ion battery system (size 3.5 MWh) is used to store the electricity surplus and the grid-connection of the PV plant allows to export the electricity excess that cannot be stored in the battery system. The economic analysis has been performed by estimating the levelized cost of hydrogen (LCOH) that is an important economic indicator based on the evaluation of investment, operational & maintenance and replacement costs. Results highlighted that the proposed on-site configuration in which the green hydrogen production is assured, is characterized by a LCOH of 10.71 €/kg.

Double and Charge-Transfer Excitations in Time-Dependent Density Functional Theory

Time-dependent density functional theory has emerged as a method of choice for calculations of spectra and response properties in physics, chemistry, and biology, with its system-size scaling enabling computations on systems much larger than otherwise possible. While increasingly complex and interesting systems have been successfully tackled with relatively simple functional approximations, there has also been increasing awareness that these functionals tend to fail for certain classes of approximations. Here I review the fundamental challenges the approximate functionals have in describing double excitations and charge-transfer excitations, which are two of the most common impediments for the theory to be applied in a black-box way. At the same time, I describe the progress made in recent decades in developing functional approximations that give useful predictions for these excitations. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 73 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Scalable Adaptive Protein Ensemble Refinement Integrating Flexible Fitting

Recent advances in cryo-electron microscopy (cryo-EM) has enabled modeling macromolecular complexes that are essential components of life. The density maps obtained from cryo-EM experiments is often integrated with ab-initio, knowledge-driven or first principles-based computational methods to build, fit and refine protein structures inside the electron density maps. Going beyond a single stationary-structure determination scheme, it is becoming more common to interpret the experimental data with a set of multiple physical models all of which contributes to the average observation seen by the experiment. Hence, there is a need to decide on the quality of an ensemble of protein structures on-the-fly, while refining them against the density maps. In this work, we demonstrate such adaptive decision making capabilities during flexible fitting of biomolecules. Our solution uses RADICAL tools (RCT) and we test this new implementation in exascale high performance computing environment for two proteins, Adenylate Kinase (ADK) and Carbon Monoxide Dehydrogenase (CODH). Our results indicate that using multiple replicas in flexible fitting with adaptive decision making improves the overall quality of fit and model by 40 % improvement when compared against the traditional flexible fitting approach. These advances are agnostic to system-size and computing environments.

Effect of Silicon on Morpho-Physiological Attributes, Yield and Cadmium Accumulation in Two Maize Genotypes with Contrasting Root System Size and Health Risk Assessment

Background and aims Cadmium (Cd) contamination is a serious threat to plants and humans. Silicon (Si) was reported to have some alleviative effects on plant tolerance to Cd stress. However, whether Si alleviates Cd toxicity in maize genotypes with contrasting root system size are unknown. Methods Effects of Si applications (0 and 200 mg kg-1 soil) on shoot and root growth, Cd uptake and transportation under Cd treatments (0 and 20 mg kg-1 soil) were assessed at the silking and maturity of maize genotypes Zhongke11 (large-rooted) and Shengrui999 (small-rooted) in a pot experiment. Results Root dry weight, plant height and root length were significantly affected by Si addition. Root volume and average root diameter were significantly positively correlated with root Cd concentration, bioaccumulation and translocation factor, respectively, of two maize genotypes at the silking stage. Addition of Si significantly increased Cd concentration, content, bioconcentration and translocation factor in roots of Zhongke11, but reduced the values of these parameters in Shengrui9999 at both growth stages. Under Cd stress, grain Cd concentration in the Si treatment was decreased by 14.4% (Zhongke11) and 21.4% (Shengrui999) than that in non-Si treatment. Grain yield was significantly negatively correlated with root Cd accumulation. Moreover, addition of Si significantly reduced Cd daily intake and health risk index in maize.Conclusions This study demonstrated that addition of Si reduced health risk by eliminating Cd accumulation in maize shoot and grain, and alleviated Cd stress with more profound effects in the small-rooted genotype Shengrui999.

Review on Relationship Between the Universality Class of the Kardar-Parisi-Zhang Equation and the Ballistic Deposition Model

We have analysed the research findings on the universality class and discussed the connection between the Kardar-Parisi-Zhang (KPZ) universality class and the ballistic deposition model in microscopic rules. In one dimension and 1+1 dimensions deviations are not important in the presence of noise. At the same time, they are very relevant for higher dimensions or deterministic evolution. Mostly, in the analyses a correction scale higher than 1280 has not been studied yet. Therefore, the growth of the interface for finite system size β ≥ 0.30 value predicted by the KPZ universality class is still predominant. Also, values of α ≥ 0.40, β ≥ 0.30, and z ≥ 1.16 obtained from literature are consistent with the expected KPZ values of α = 1/2, β = 1/3, and z = 3/2. A connection between the ballistic deposition and the KPZ equation through the limiting procedure and by applying the perturbation method was also presented.