A coherent approach to the description of double excitations in correlated materials is presented: We derive stringent mathematical conditions on the algebraical structure of the Bethe-Salpeter and ...time-dependent density functional theory kernels that avoid the occurrence of spurious and nonphysical excitations. We discuss how these conditions need to be respected at any level of approximation, including the commonly used local density and static screening approximations. We propose a correlated kernel for the Bethe-Salpeter equation, and we illustrate several aspects of our approach with numerical calculations for model molecular systems.
We have recently completed a full re-architecturing of the ROSETTA molecular modeling program, generalizing and expanding its existing functionality. The new architecture enables the rapid ...prototyping of novel protocols by providing easy-to-use interfaces to powerful tools for molecular modeling. The source code of this rearchitecturing has been released as ROSETTA3 and is freely available for academic use. At the time of its release, it contained 470,000 lines of code. Counting currently unpublished protocols at the time of this writing, the source includes 1,285,000 lines. Its rapid growth is a testament to its ease of use. This chapter describes the requirements for our new architecture, justifies the design decisions, sketches out central classes, and highlights a few of the common tasks that the new software can perform.
A new highly solid-state luminescent phase of a previously reported weakly luminescent Cu
Pd
dicationic assembly is reported revealing the high geometrical versatility of this moiety that importantly ...alters its luminescent properties. This very minor new species B
is based on a different conformer scaffold than the one encountered in the previously reported B
form and, essentially differs from B
by displaying shorter Cu
-Cu
intermetallic distances. DFT calculations allow concluding that the predominance in the solid-state of the weakly luminescent and less stable B
phase is due to the extra stability induced by a larger number of intermolecular non-covalent π-CH interactions in its crystalline packing and not by the intrinsic stability of the Cu
Pd
dicationic moiety. Calculations also revealed that a more stable conformation B
is expected in vacuum, which bears a different distribution of Cu
-Cu
intermetallic distances than the dications in B
and B
phases. Taking into account that the geometrical alterations are associated to drastic changes of luminescence properties, this confer to the Cu
Pd
assembly high potentiality as stimuli-sensitive luminescent materials. Indeed, by applying mechanical or thermal stress to samples of B
phase, new phases B
and B
, respectively, were obtained. Alterations of the solid-state photophysical properties of these new species compared to those recorded for B
are reported together with a combined experimental and computed study of the structures/properties relationships observed in these phases.
Artificial switchable catalysts Blanco, Victor; Leigh, David A; Marcos, Vanesa
Chemical Society reviews,
08/2015, Volume:
44, Issue:
15
Journal Article
Peer reviewed
Open access
Catalysis is key to the effective and efficient transformation of readily available building blocks into high value functional molecules and materials. For many years research in this field has ...largely focussed on the invention of new catalysts and the optimization of their performance to achieve high conversions and/or selectivities. However, inspired by Nature, chemists are beginning to turn their attention to the development of catalysts whose activity in different chemical processes can be switched by an external stimulus. Potential applications include using the states of multiple switchable catalysts to control sequences of transformations, producing different products from a pool of building blocks according to the order and type of stimuli applied. Here we outline the state-of-art in artificial switchable catalysis, classifying systems according to the trigger used to achieve control over the catalytic activity and stereochemical or other structural outcomes of the reaction.
This review describes progress in the field of artificial switchable catalysts, where the rate acceleration, stereochemistry and/or chemoselectivity of catalysed processes can be switched through external stimuli.
When a large set of discrete bodies passes through a bottleneck, the flow may become intermittent due to the development of clogs that obstruct the constriction. Clogging is observed, for instance, ...in colloidal suspensions, granular materials and crowd swarming, where consequences may be dramatic. Despite its ubiquity, a general framework embracing research in such a wide variety of scenarios is still lacking. We show that in systems of very different nature and scale -including sheep herds, pedestrian crowds, assemblies of grains, and colloids- the probability distribution of time lapses between the passages of consecutive bodies exhibits a power-law tail with an exponent that depends on the system condition. Consequently, we identify the transition to clogging in terms of the divergence of the average time lapse. Such a unified description allows us to put forward a qualitative clogging state diagram whose most conspicuous feature is the presence of a length scale qualitatively related to the presence of a finite size orifice. This approach helps to understand paradoxical phenomena, such as the faster-is-slower effect predicted for pedestrians evacuating a room and might become a starting point for researchers working in a wide variety of situations where clogging represents a hindrance.
Virtual Chemical Libraries Walters, W Patrick
Journal of medicinal chemistry,
02/2019, Volume:
62, Issue:
3
Journal Article
Peer reviewed
Advances in computer processing speed and storage capacity have enabled researchers to generate virtual chemical libraries containing billions of molecules. While these numbers appear large, they are ...only a small fraction of the number of organic molecules that could potentially be synthesized. This review provides an overview of recent advances in the generation and use of virtual chemical libraries in medicinal chemistry. We also consider the practical implications of these libraries in drug discovery programs and highlight a number of current and future challenges.
The reactions of the organometallic ligand complex Cp
Mo
(CO)
(μ,η
-Sb
) (C) with AgTEF (TEF
=Al{OC(CF
)
}
) in the presence of a number of di- or polytopic N-donor molecules ...(1,6,7,12-tetraazaperylene (L1), 2,2'-bipyrimidine (L2), 4,4'-bipyridine (L3), trans-1,2-di(4-pyridyl)ethylene (L4) and 1,3-di(4-pyridyl)propane (L5)), were studied. Depending on the reaction stoichiometry and choice of linker, these reactions lead to the selective formation of dimeric or tetrameric supramolecular coordination complexes as well as 1D and 2D coordination polymers (CPs). The presented compounds are unique examples of supramolecular complexes incorporating both organometallic Sb-donor and organic N-donor molecules as ligands to stabilize metal ions. Moreover, one of the formed compounds, the CP Ag
(η
-C)
(L4)
TEF
, represents an exceptional 1D polymer incorporating both N- and Sb-donor ligands as connectors for metal ions.
Materials with switchable mechanical properties are widespread in living organisms and endow many species with traits that are essential for their survival. Many of the mechanically morphing ...materials systems found in nature are based on hierarchical structures, which are the basis for mechanical robustness and often also the key to responsive behavior. Many “operating principles” involve cascades of events that translate cues from the environment into changes of the overall structure and/or the connectivity of the constituting building blocks at various levels. These concepts permit dramatic property variations without significant compositional changes. Inspired by the function and the growing understanding of the operating principles at play in biological materials with the capability to change their mechanical properties, significant efforts have been made toward mimicking such architectures and functions in artificial materials. Research in this domain has rapidly grown in the last two decades and afforded many examples of bioinspired materials that are able to reversibly alter their stiffness, shape, porosity, density, or hardness upon remote stimulation. This review summarizes the state of research in this field.
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