Lanthanum- Oligopyrrole Complexes (neutral, III) for biogas capture applications by DFT

The structures and interactions of systems formed by the MPBCP (meta-Phenylene-Bridged Cyclic Oligopyrrole) functionalized with lanthanum atom were studied for investigating the abilities of MPBCP, [La-MPBCP]+3 and La-MPBCP to absorb biogas (CO2, N2, H2 and CH4) using density functional theory. The Eads calculated values for biogas molecules on [La-MPBCP]+3 and La-MPBCP showed that these gas molecules have favorable interactions with the lanthanum atom coordinated on the MPBCP. CO2 molecule shows strong interactions, with Eads values of -28.63 and -15.95 kcal/mol. In the case of H2 molecule, the Eads is lower with values of -7.51 and -5.28. It is easy to observe the CO2 molecule on the [La-MPBCP]+3 system has four times higher energy value than adsorption energy for the H2 molecule. The natural bond orbital analysis reveals that gas molecules are electron donator in the systems and the acceptor orbitals belong to lanthanum atom. Computational studies suggest that CO2, N2, CH4 and H2 molecules on [La-MPBCP]+3 and La-MPBCP present physisorption. Our findings divulge promising potential of the [La-MPBCP]+3 as an adsorber/separator CO2/H2.

Sorption of molecular hydrogen on the graphene-like matrix doped by N- and B-atoms

The regularities of interaction of hydrogen molecules with graphene-like planes, where two carbon atoms are replaced by nitrogen or boron atoms, have been studied by the methods of quantum chemistry (DFT, B3LYP, 6-31G**). To take into account the dispersion contributions to the energy of formation of intermolecular complexes that occur during the formation of adsorption supramolecular structures, Grimme’ dispersion correction is used - D3. To study the effect of the size of a graphene-like cluster on the energy of molecular hydrogen chemisorption, polyaromatic molecules (PAM) are used of pyrene, coronene and that consisting of 54 carbon atoms, as well as their nitrogen- and boron-containing analogues where N- and B-atoms are placed in a para-position relative to each other, in the so-called piperazine configuration. The insertion of a heteroatom changes the structure of the transition state and the mechanism of chemisorption. An analysis of the results of quantum chemical calculations showed the highest exothermic dissociative adsorption of the H2 molecule on B-containing graphene-like ones. For N-containing PAM, the exothermicity of the mentioned reaction is somewhat lower, for it a possibility of desorption of atomic hydrogen desorption the surface of the latter with subsequent recombination in the gas phase has been also shown. At the same time, for models of pure graphene-like layer, the data obtained indicate the impossibility of chemisorption of molecular hydrogen. Without a complete analysis of the results for all the possible locations of the pair of hydrogen atoms (formed due to dissociation of the H2 molecule) bound by nitrogen-containing polyaromatic molecules, it can be noted that the dissociative chemisorption of the H2 molecule, regardless of the nature of heteroatom in the PAM, is thermodynamically more probable at the periphery of the model molecules than that in their centers.

A paradigm system for strong correlation and charge transfer competition

In chemistry and condensed matter physics the solution of simple paradigm systems, such as the hydrogen atom and the uniform electron gas, plays a critical role in understanding electron behaviors and developing electronic structure methods. The H2 molecule is a paradigm system for strong correlation with a spin-singlet ground state that localizes the two electrons onto opposite protons at dissociation. We extend H2 to a new paradigm system by using fractional nuclear charges to break the left-right nuclear symmetry, thereby enabling the competition between strong correlation and charge transfer that drives the exotic properties of many materials. This modification lays a foundation for improving practical electronic structure theories and provides an extendable playground for analyzing how the competition appears and evolves.

Hybrid Quantum-Classical Eigensolver without Variation or Parametric Gates

The use of near-term quantum devices that lack quantum error correction, for addressing quantum chemistry and physics problems, requires hybrid quantum-classical algorithms and techniques. Here, we present a process for obtaining the eigenenergy spectrum of electronic quantum systems. This is achieved by projecting the Hamiltonian of a quantum system onto a limited effective Hilbert space specified by a set of computational bases. From this projection, an effective Hamiltonian is obtained. Furthermore, a process for preparing short depth quantum circuits to measure the corresponding diagonal and off-diagonal terms of the effective Hamiltonian is given, whereby quantum entanglement and ancilla qubits are used. The effective Hamiltonian is then diagonalized on a classical computer using numerical algorithms to obtain the eigenvalues. The use case of this approach is demonstrated for ground state and excited states of BeH2 and LiH molecules, and the density of states, which agrees well with exact solutions. Additionally, hardware demonstration is presented using IBM quantum devices for H2 molecule.

A panchromatic spatially resolved analysis of nearby galaxies – II. The main sequence – gas relation at sub-kpc scale in grand-design spirals

ABSTRACT In this work, we analyse the connection between gas availability and the position of a region with respect to the spatially resolved main-sequence (MS) relation. Following the procedure presented in Enia et al. (2020), for a sample of five face-on, grand design spiral galaxies located on the MS we obtain estimates of stellar mass and star formation rate surface densities (Σ⋆ and ΣSFR) within cells of 500 pc size. Thanks to H i 21cm and 12CO(2–1) maps of comparable resolution, within the same cells we estimate the surface densities of the atomic (ΣH i) and molecular ($\Sigma _{\rm {H_2}}$) gas and explore the correlations among all these quantities. Σ⋆, ΣSFR, and $\Sigma _{\rm {H_2}}$ define a 3D relation whose projections are the spatially resolved MS, the Kennicutt–Schmidt law and the molecular gas MS. We find that $\Sigma _{\rm {H_2}}$ steadily increases along the MS relation and is almost constant perpendicular to it. ΣH i is nearly constant along the MS and increases in its upper envelope. As a result, ΣSFR can be expressed as a function of Σ⋆ and ΣH i, following the relation log ΣSFR = 0.97log Σ⋆ + 1.99log ΣH i − 11.11. We show that the total gas fraction significantly increases towards the starburst regions, accompanied by a weak increase in star formation efficiency. Finally, we find that H2/H i varies strongly with the distance from the MS, dropping dramatically in regions of intense star formation, where the UV radiation from newly formed stars dissociates the H2 molecule, illustrating the self-regulating nature of the star formation process.