Developing visual perception models for active agents and sensorimotor control in the physical world are cumbersome as existing algorithms are too slow to efficiently learn in real-time and robots ...are fragile and costly. This has given rise to learning-in-simulation which consequently casts a question on whether the results transfer to real-world. In this paper, we investigate developing real-world perception for active agents, propose Gibson Environment for this purpose, and showcase a set of perceptual tasks learned therein. Gibson is based upon virtualizing real spaces, rather than artificially designed ones, and currently includes over 1400 floor spaces from 572 full buildings. The main characteristics of Gibson are: I. being from the real-world and reflecting its semantic complexity, II. having an internal synthesis mechanism "Goggles" enabling deploying the trained models in real-world without needing domain adaptation, III. embodiment of agents and making them subject to constraints of physics and space.
The stability and geometry of a hydrogen‐bonded dimer is traditionally attributed mainly to the central moiety AH⋅⋅⋅B, and is often discussed only in terms of electrostatic interactions. The ...influence of substituents and of interactions other than electrostatic ones on the stability and geometry of hydrogen‐bonded complexes has seldom been addressed. An analysis of the interaction energy in the water dimer and several alcohol dimers—performed in the present work by using symmetry‐adapted perturbation theory—shows that the size and shape of substituents strongly influence the stabilization of hydrogen‐bonded complexes. The larger and bulkier the substituents are, the more important the attractive dispersion interaction is, which eventually becomes of the same magnitude as the total stabilization energy. Electrostatics alone are a poor predictor of the hydrogen‐bond stability trends in the sequence of dimers investigated, and in fact, dispersion interactions predict these trends better.
Predicting hydrogen‐bond strength: The interaction energy of the dimer of water and those of various alcohols is investigated by using symmetry‐adapted perturbation theory. Other than electrostatic interactions, exchange, induction, and dispersion interactions are also important. The picture shows the dependence of the interaction contributions on intermolecular separation for the tert‐butanol dimer.
Bonding in the C2 molecule is investigated with CAS(8,8) wave functions using canonical MOs. In a subsequent step, orthogonal atomic orbitals are constructed by localizing the CASSCF MOs on the two ...carbon atoms with an orthogonal transformation. This orbital transformation causes an orthogonal transformation of the configuration state functions (CSF) spanning the function space of the singlet ground state of C2. Instead of CSFs built from canonical MOs, one obtains CSFs of orthogonal deformed atomic orbitals (AO). This approach resembles the orthogonal valence bond (OVB) methods’ CSFs, which are very different from the conventional VB, based on non-orthogonal AOs. To become used to the different argumentation, the bonding situations in ethane (single bond), ethene (double bond), and the nitrogen molecule (triple bond) are also studied. The complex bonding situation in C2 is caused by the possibility to excite an electron with a spin flip from the doubly occupied 2s AO into the 2p subshell, and the resulting high-spin 5Su state of the carbon atom allows for a better reduction of the Pauli repulsion. However, the electron structure around the equilibrium distance does not allow one to say that C2 in its ground state has a double, or triple, or even a quadruple bond.
Adhesive forces were investigated in a computational study for the complexes of graphene with each of the four adsorbates, benzene, anthracene, pyrene, and tetracene, by using the DFT method B3LYP ...and the semiempirical method DFTB, together with empirical dispersion corrections. The four aromatic molecules differ in size and flexibility. Whereas the adhesion energy (for complete separation) is independent of the way an adsorbed molecule is separated from graphene, the maximum adhesive forces depend strongly on the way the adsorbate is lifted. We investigated, therefore, four lifting modes: in rigid vertical lifting, all atoms of the adsorbate are pull-off points; in flexible central lifting, the pull-off points are in the middle of the adsorbate; in both rigid and flexible terminal lifting, the pull-off points are at one end and the adsorbate is regarded as being either rigid or flexible. For the systems investigated, we find that, for both the adhesion energies and the maximum adhesive forces, the DFTB results are at most 10% lower than the corresponding DFT results. For small or rigid molecules like benzene and pyrene, there is no significant difference between rigid vertical and flexible central lifting. For a flexible molecule like tetracene, the difference of the maximum adhesive force can be up to 70%. Terminal lifting consists of two subprocesses. For the second subprocess, both the adhesion energy and the maximum adhesive force are essentially unchanged across all four adsorbates; for the first subprocess, however, we find a pronounced size dependence of the adhesion energy.
Chemical bonding is the stabilization of a molecular system by charge- and spin-reorganization processes in chemical reactions. These processes are said to be local, because the number of atoms ...involved is very small. With multi-configurational self-consistent field (MCSCF) wave functions, these processes can be calculated, but the local information is hidden by the delocalized molecular orbitals (MO) used to construct the wave functions. The transformation of such wave functions into valence bond (VB) wave functions, which are based on localized orbitals, reveals the hidden information; this transformation is called a VB reading of MCSCF wave functions. The two-electron VB wave functions describing the Lewis electron pair that connects two atoms are frequently called covalent or neutral, suggesting that these wave functions describe an electronic situation where two electrons are never located at the same atom; such electronic situations and the wave functions describing them are called ionic. When the distance between two atoms decreases, however, every covalent VB wave function composed of non-orthogonal atomic orbitals changes its character from neutral to ionic. However, this change in the character of conventional VB wave functions is hidden by its mathematical form. Orthogonal VB wave functions composed of orthonormalized orbitals never change their character. When localized fragment orbitals are used instead of atomic orbitals, one can decide which local information is revealed and which remains hidden. In this paper, we analyze four chemical reactions by transforming the MCSCF wave functions into orthogonal VB wave functions; we show how the reactions are influenced by changing the atoms involved or by changing their local symmetry. Using orthogonal instead of non-orthogonal orbitals is not just a technical issue; it also changes the interpretation, revealing the properties of wave functions that remain otherwise undetected.
Reliable simulation of molecular adsorption onto cellulose surfaces is essential for the design of new cellulose nanocomposite materials. However, the applicability of classical force field methods ...to such systems remains relatively unexplored. In this study, we present the adsorption of glucose, cellobiose, and cellotetraose on model surfaces of crystalline cellulose Iα and Iβ. The adsorption of the two large carbohydrates was simulated with the GLYCAM06 force field. To validate this approach, quantum theoretical calculations for the adsorption of glucose were performed: Equilibrium geometries were studied with density functional theory (DFT) and dispersion-corrected DFT, whereas the adsorption energies were calculated with two standard density functional approximations and five dispersion-containing DFT approaches. We find that GLYCAM06 gives a good account of geometries and, in most cases, accurate adsorption energies when compared to dispersion-corrected DFT energies. Adsorption onto the (100) surface of cellulose Iα is, in general, stronger than onto the (100) surface of cellulose Iβ. Contrary to intuition, the adsorption energy is not directly correlated with the number of hydrogen bonds; rather, it is dominated by dispersion interactions. Especially for bigger adsorbates, a neglect of these interactions leads to a dramatic underestimation of adsorption energies.
Carbon nanotubes (CNTs) are insoluble in small aromatics, but solubilisation is possible when special solubilisers are added to the solvent. The solubiliser molecules are composed of a large aromatic ...moiety, which adsorbs to the CNT, and a solvophilic group connected by a short aliphatic chain. The experimental finding that CNTs can be solubilised but not dissolved lets one assume that a strong interaction of the solubiliser molecules with the CNT is necessary for the solubilisation. The form of the solubiliser molecules and the need that the aromatic moiety must contain at least three condensed aromatic rings suggest that (1) the aromatic moiety interacts with the CNT, (2) the solvophilic group interacts with the bulk and (3) the solubilised CNTs are dressed by the strongly interacting solubiliser molecules. Strength of the interactions between CNT and the aromatic moiety can be described by either the interaction energy or the force needed to pull the aromatic molecule off the CNT. Although we do not find a size dependence of the desorption energies, we find a marked size dependence of the adhesive forces.
Weak, intermolecular interactions in amine dimers were studied by using the combination of a dispersionless density functional and a function that describes the dispersion contribution to the ...interaction energy. The validity of this method was shown by comparison of structural and energetic properties with data obtained with a conventional density functional and the coupled cluster method. The stability of amine dimers was shown to depend on the size, the shape, and the relative orientation of the alkyl substituents, and it was shown that the stabilization energy for large substituents is dominated by dispersion interactions. In contrast to traditional chemical explanations that attribute stability and condensed matter properties solely to hydrogen bonding and, thus, to the properties of the atoms forming the hydrogen bridge, we show that without dispersion interactions not even the stability and structure of the ammonia dimer can be correctly described. The stability of amine dimers depends crucially on the interaction between the non‐polar alkyl groups, which is dominated by dispersion interactions. This interaction is also responsible for the energetic part of the free energy interaction used to describe hydrophobic interactions in liquid alkanes. The entropic part has its origin in the high degeneracy of the interaction energy for complexes of alkane molecules, which exist in a great variety of conformers, having their origin in internal rotations of the alkane chains.
An incremental increase of the intermolecular dispersion interaction energy in an n‐butylamine dimer with cis‐aligned substituents is reported. The dispersion interaction energy is calculated for all atom pairs inside a sphere with radius RS; the center of the sphere is the midpoint of the N−N distance. The graph shows that the constant increase of the interaction energy with increasing radius is due to the added atom pairs in close contact.
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•What is meant by “topological approach”?•“Topological approach” and chemical concepts.•Measurable quantities from “topological approaches”.•Predicting the outcome of a “topological ...approach”.•New domains of application.
The paper collects the answers of the authors to the following questions:
•What is the significance of topological approach?•Can new chemical concepts be found by a topological approach?•What is the status of a chemical concept within a topological approach?•Should topological approaches provide measurable quantities?•Is it possible to predict the outcome of a topological approach without performing a calculation on a computer?•What are new domains for which topological approaches would be useful?
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