How many electrons form chemical bonds in the NgBeS (Ng = Ar, Kr, Xe) molecules? Topological study using the electron localisation function (ELF) and electron localisability indicator (ELI-D)

Nature of bonding in the NgBeS (Ng = Ar, Kr, Xe) molecules has been studied using topological analysis of ELF, ELI-D functions with the wave function approximated at the DFT (M062X, B3LYP + ZORA), MP2, CCSD and CASSCF level of calculations. Both Xe–Be and Be=S bonds display topological features typical for the covalent-dative bonding. The V2(Xe) attractor characterising electron density, involved in interaction with the beryllium atom, is closer to the C(Be) core than to C(Xe). The population of the respective basin ranges between 1.59e (B3LYP + ZORA) and 1.83e (CCSD). The beryllium–sulphur bond is described by the bonding disynaptic basin V(Be,S) with the population between 3.22e (CASSCF) and 3.48e (M062X). The approximate weights for the Be–S and Be=S resonance forms are 0.3 and 0.7, respectively, in all molecules. Both the NgBe and BeS bonds are highly polarised with the values of the p SBe and p NgBe polarity indices (CCSD) of 0.8 and 0.9–1.0 for all studied molecules

The nature of the T=T double bond (T = B, Al, Ga, In) in dialumene and its derivatives: topological study of the electron localization function (ELF)

The local electronic structure of the Al=Al bond was studied in dialumene and derivatives of dialumene in which the Al atoms were substituted by B, Ga, or In atoms. DFT calculations were performed using the B3LYP, B3PW91, PBE0, M06-L, and M06-2X functionals. Topological analysis of the electron localization function described the covalent bonds mentioned above using the disynaptic basins Vi=1,2(B,B), Vi=1,2(Al,Al), V(Ga,Ga), and Vi=1,2(In,In). The basin populations were smaller than 4 e, as expected for a double bond: B=B 2.97 e, Al=Al 3.44–3.5 e, Ga=Ga 3.58 e, and In=In 3.86 e. The Al=Al, Ga=Ga, and In=In bonds were found to be intermediate in character between single and double bonds. Topological analysis of the ρ(r) field for dialumene showed a non-nuclear attractor along the Al=Al bond, with a pseudoatom basin population of 0.937 e. NBO analysis suggested that a double bond occurred only in the molecules containing Al, Ga, or In atoms. The character of the Ga=Ga bond was observed to be strongly dependent on the effective core potential used in the calculations

The nature of multiple boron-nitrogen bonds studied using electron localization function (ELF), electron density (AIM), and natural bond orbital (NBO) methods

Local nature of the boron-nitrogen (BN) bonding with different formal multiplicities (B≡N, B=N, B-N) have been investigated for 25 experimentally established organoboron molecules in both real and the Hilbert space, using topological analysis of electron localization function (ELF), electron density (AIM), and natural bond orbital (NBO) method. Each BN bond has been represented (ELF) by the bonding disynaptic attractor V(B,N), with the basin electron population between 5.72e and 1.83e, confirming possible existence of all the three bond types. A covalent character of bonding can be associated with the dative mechanism due to the V(B,N) bonding basin formed mainly (91–96%) by the N electron density. Similarly, the NBO method shows 2-center natural orbitals, consisting largely of the hybrids from the N atom. The AIM analysis yields the features typical for shared (H(3,−1)(r)  0) interactions. The delocalization indices, describing electron exchanges between B and N quantum atoms, are smaller than 1.5, even for formally very short triple B≡N bonds

Topological analysis of the electron localisation function (ELF) applied to the electronic structure of oxaziridine: the nature of N-O bond

Topological analysis of the electron localisation function (ELF), natural bond orbital and Wiberg bond index calculations have been applied to study the electronic structure of the oxaziridine molecule with a special focus on the nitrogen-oxygen bond. The calculations have been performed at the DFT(B3LYP, CAM-B3LYP, ωB97XD, M06-L, M06-2X) and post-Hartree-Fock (CCSD(T) and CASSCF) computational levels with applied aug-cc-pVTZ basis set. Nature of N-O bonding has been characterised by two resonance forms, N+ O− and N−O+, owing to a very small population (< 0.60e) of the bonding basin V(N,O), localised in the ELF field for the N-O region. The importance of electron correlation effects for the description of the N-O bonding has been observed in the CASSCF calculations. The orbital description (Wiberg, NBO) differs from topological characterisation, indicating a single N-O bond

Characterisation of the reaction mechanism between ammonia and formaldehyde from the topological analysis of ELF and catastrophe theory perspective

A prototypical reaction between ammonia and formaldehyde has been investigated at the DFT(M06)/6- 311++G(d,p) computational level using the Bonding Evolution Theory (BET). BET is a very useful tool for studying reaction mechanisms as it combines topological analysis of electron localisation function with the catastrophe theory. Each of two studied reactions: H2C=O + NH3 ↔ HO–C(H2)– NH2 (hemiaminal) and HO–C(H2)–NH2 ↔ HN = CH2 (Schiff base) + H2O consists of six steps. Formation of hemiaminal starts from a nucleophillic attack of nitrogen lone pair in NH3 on the carbon atom in H2C=O and is subsequently followed by hydrogen transfer within the N–H..O bridge. A Schiff base is formed via the dehydration reaction of the hemiaminal, where the C–O bond is broken first, followed by hydrogen transfer towards the [HO]δ− moiety, resulting in water and methanimine. The present paper focuses on differences in reaction mechanisms for the processes described above. The results have been compared to the reaction mechanism for stable hemiaminal synthesis from benzaldehyde and 4- amine-4H-1,2,4-triazole studied previously using the BET theor

The nature of inter- and intramolecular interactions in F2OXe…HX (X= F, Cl, Br, I) complexes

Electronic structure of the XeOF2 molecule and its two complexes with HX (X= F, Cl, Br, I) molecules have been studied in the gas phase using quantum chemical topology methods: topological analysis of electron localization function (ELF), electron density, ρ(r), reduced gradient of electron density |RDG(r)| in real space, and symmetry adapted perturbation theory (SAPT) in the Hilbert space. The wave function has been approximated by the MP2 and DFT methods, using APF-D, B3LYP, M062X, and B2PLYP functionals, with the dispersion correction as proposed by Grimme (GD3). For the Xe-F and Xe=O bonds in the isolated XeOF2 molecule, the bonding ELF-localization basins have not been observed. According to the ELF results, these interactions are not of covalent nature with shared electron density. There are two stable F2OXe…HF complexes. The first one is stabilized by the F-H…F and Xe…F interactions (type I) and the second by the F-H…O hydrogen bond (type II). The SAPT analysis confirms the electrostatic term, Eelst (1) and the induction energy, Eind (2) to be the major contributors to stabilizing both types of complexes

Predviđanje zakrivljenosti bimetalne limene ploče Al-Cu tijekom asimetričnog hladnog valjanja

In the paper, solving a problem of rolling Al-Cu plates by the numerical way is presented. In the development of new technologies in rolling of bimetallic plates there are many problems both with ensuring a uniform strain distribution and producing a straight plate as well. Such a solution within research of the numerical simulation was obtained at the Forge 2 program based on finite element method. The cold rolling process was carried out at the temperature of 20 °C for 10 %, 20 % and 25 % relative rolling reduction. The curvature of bimetallic plate was numerically controlled by changing the speed of one roll. In this article the numerical analysis of asymmetrical rolling processes of plate composed with two metal layers, Al and Cu, has been done. At the work an influence of rotary speed ratio and value deformation on change of curvature bimetallic plate is determined.U radu je predstavljen numerički način rješavanja valjanja Al-Cu limenih ploča. U razvoju novih tehnologija za valjanje bimetalnih ploča ima mnogo problema i u osiguravanju jednolikog rasporeda deformacije i u proizvodnji ravnih ploča. U okviru provedenih istraživanja programa Forge 2, baziranom na metodi konačnih elemenata, ostvarena je numerička simulacija. Proces hladnog valjanja proveden je na temperaturi od 20 °C s relativnom redukcijom valjanja od 10 %, 20 % i 25 %. Zakrivljenost bimetalne ploče kontrolirala se numeričkim mijenjanjem brzine valjaka. U ovom članku napravljena je numerička analiza procesa asimetričnog valjanja ploče sastavljene od dva metal nasloja: Al i Cu. Također je utvrđen utjecaj omjera brzine rotacije i vrijednosti deformacije na promjenu zakrivljenosti metalne ploče

Odabir parametara kovanja i oblika alata sa stajališta poboljšanja kakvoće otkivka

The article discusses the effect of symmetrical and asymmetrical forging processes on the homogenization of the values of local deformations within the entire cross-section of a forging. Theoretical studies have been performed for the plane strain deformation state, the results of which have been verified in laboratory conditions. From the tests, the values of the main technological parameters of forging have been determined and an appropriate group of tools has been proposed to be used for the anvil hammering of forgings.U članku se raspravlja o utjecaju simetričnog i asimetričnog procesa kovanja na homogenizaciju vrijednosti lokalnih deformacija unutar cijelog presjeka otkivka. Provedene su teorijske studije glede stanja deformacije pri površinskom istezanju čiji rezultati su potvrđeni u laboratorijskim uvjetima. Na osnovu provedenih pokusa utvrđene su vrijednosti glavnih tehnoloških parametara kovanja i predložena je odgovarajuća grupa alata za uporabu pri kovanju otkivaka u ukovnjima

Kompjutersko i laboratorijsko modeliranje analize sprečavanja metalurških grešaka na ingotima tijekom slobodnog toplog kovanja

Computer modelling using a FEM-based program, Forge 2DŇ, was carried out in the study. The influence of die shape and the main parameters of the forging process on closing up of metallurgical defects were determined.U studiji je provedeno kompjutorsko programiranje uporabom programa Forge 2DŇ temeljenog na MKE. Laboratorijsko modeliranje procesa slobodnog toplog kovanja u profilnim nakovnjima provedeno je radi sprečavanja metalurških kvarova. Rezultati dobiveni simulacijom i laboratorijskim modeliranjem obrađeni su uporabom komercijalnih paketa za statističku obradu, Statistica 6.0® PL. Utvrđen je utjecaj oblika matrica i glavnih parametara procesa kovanja na sprečavanju metalurških grešaka

Hydrogen bonding in infinite hydrogen fluoride and hydrogen chloride chains

Hydrogen bonding in infinite HF and HCl bent (zigzag) chains is studied using the ab initio coupled-cluster singles and doubles (CCSD) correlation method. The correlation contribution to the binding energy is decomposed in terms of nonadditive many-body interactions between the monomers in the chains, the so-called energy increments. Van der Waals constants for the two-body dispersion interaction between distant monomers in the infinite chains are extracted from this decomposition. They allow a partitioning of the correlation contribution to the binding energy into short- and long-range terms. This finding affords a significant reduction in the computational effort of ab initio calculations for solids as only the short-range part requires a sophisticated treatment whereas the long-range part can be summed immediately to infinite distances.Comment: 9 pages, 4 figures, 3 tables, RevTeX4, corrected typo