Doubly hybrid density functional for accurate descriptions of nonbond interactions, thermochemistry, and thermochemical kinetics

We develop and validate a density functional, XYG3, based on the adiabatic connection formalism and the Görling–Levy coupling-constant perturbation expansion to the second order (PT2). XYG3 is a doubly hybrid functional, containing 3 mixing parameters. It has a nonlocal orbital-dependent component in the exchange term (exact exchange) plus information about the unoccupied Kohn–Sham orbitals in the correlation part (PT2 double excitation). XYG3 is remarkably accurate for thermochemistry, reaction barrier heights, and nonbond interactions of main group molecules. In addition, the accuracy remains nearly constant with system size

Gas adsorption in active carbons and the slit-pore model 1 : pure gas adsorption

We describe procedures based on the polydisperse independent ideal slit-pore model, Monte Carlo simulation and density functional theory (a 'slab-DFT') for predicting gas adsorption and adsorption heats in active carbons.A novel feature of this work is the calibration of gas-surface interactions to a high surface area carbon, rather than to a low surface area carbon as in all previous work. Our models are used to predict the adsorption of carbon dioxide, methane, nitrogen, and hydrogen up to 50 bar in several active carbons at a range of near-ambient temperatures based on an analysis of a single 293 K carbon dioxide adsorption isotherm. The results demonstrate that these models are useful for relatively simple gases at near-critical or supercritical temperatures

Gas adsorption in active carbons and the slit-pore model 2 : mixture adsorption prediction with DFT and IAST

We use a fast density functional theory (a 'slab-DFT') and the polydisperse independent ideal slit-pore model to predict gas mixture adsorption in active carbons. The DFT is parametrized by fitting to pure gas isotherms generated by Monte Carlo simulation of adsorption in model graphitic slit-pores. Accurate gas molecular models are used in our Monte Carlo simulations with gas-surface interactions calibrated to a high surface area carbon, rather than a low surface area carbon as in all previous work of this type, as described in part 1 of this work (Sweatman, M. B.; Quirke, N. J. Phys. Chem. B 2005, 109, 10381). We predict the adsorption of binary mixtures of carbon dioxide, methane, and nitrogen on two active carbons up to about 30 bar at near-ambient temperatures. We compare two sets of results; one set obtained using only the pure carbon dioxide adsorption isotherm as input to our pore characterization process, and the other obtained using both pure gas isotherms as input. We also compare these results with ideal adsorbed solution theory (IAST). We find that our methods are at least as accurate as IAST for these relatively simple gas mixtures and have the advantage of much greater versatility. We expect similar results for other active carbons and further performance gains for less ideal mixtures

New Synthetic Strategies for Improved Gas separation by Nanoporous Organic Polymers

Abstract NEW SYNTHETIC STRATEGIES FOR IMPROVED GAS SEPARATION BY NANOPOROUS ORGANIC POLYMERS Suha S. Altarawneh, Ph.D. The emission of carbon dioxide (CO2) from fossil fuel combustion is a major cause of climate change. Therefore, the efficient separation of CO2 from mixtures of gases such as flue gas and impure sources of CH4 (e.g. natural gas and landfill gas) is an essential step in meeting the ever increasing demands on natural gas and creating a cleaner environment. Carbon capture and storage technology (CCS) is one of the methods employed for gas separation using chemisorption and/or physisorption processes. Several materials such as porous polymers and amine solutions have been used as gas adsorbents. However, the amount of energy required for the adsorbent regeneration is one of the main concerns that needs to be addressed. In this regard, porous organic polymers (POPs) with defined porosity and preferential binding affinity for CO2 over N2 and CH4 are some of the most attractive materials that could fulfill the above requirement and are also applicable for use in gas storage and separation. Suitable POPs that can be used for gas storage applications need to have high porosity and mechanical stability under high pressure conditions (~100 bar). Alternatively, the most effective POPs in gas separation are those that have preferential binding affinity for CO2 over other gases present at low pressure settings. In all cases, the chemical nature of POPs and their textural properties are key parameters, however, the modest surface area of most POPs limits their efficiency. With the above considerations in mind, the aim of our research is to develop benzimidazole–linked polymers (BILPs) that have variable porosity levels and chemical functionality to enhance gas separation (CO2/CH4, CO2/N2). We have established new synthetic routes that utilize polycondensation reactions between aryl-aldehydes and aryl-o-diamine building units to construct new BILPs with improved gas separation properties. Our strategy targeted structural and textural modifications of BILPs. We used longer linkers (building units) to improve porosity; however, the flexible linkers offered only low porosity due to network interpenetration. To overcome this challenge, a more controlled network growth rate was assessed by adjusting imine-bond formation rates through different acid loading. The acid, HCl, was used to catalyze imine-bond formation. The new resulting acid-catalyzed BILPs have shown an improved porosity up to 92% compared to the non-catalyzed BILPs. We also used the “rational ligand design” approach to introduce new functionalities into BILPs (-OR) to alter the hydrophobic nature of their pores. In this regard, we have illustrated the applicability of this strategy to BILPs containing flexible aryl-o-diamine linkers. The bulky alkoxy groups were incorporated into the aryl-aldehyde building unit prior to polymerization. The resulting polymers have proven that the presence of the bulky pendant alkoxy-chains plays a significant role during the polymerization process which allows for increased control over network formation, and in turn, porosity. Sorption measurements, selectivity, and heats of adsorption data have confirmed the positive impact of the alkoxy-groups and shown that varying the pendant groups is a promising method for designing highly porous BILPs. In addition to pore functionalization with alkoxy-chains, we used pi-conjugated and N-rich building units to prepare new BILPs that have semiconducting properties in addition to their porous nature. This class of BILPs has shown that the extended-conjugated system improved BILPs electronic properties. The other studies performed in this research, involved the use of DFT theory to investigate CO2/BILPs interaction sites and binding affinities. The computational outcomes of DFT have shown that (C-H) bond of the aryl system is a possible site for CO2 interaction beside the free-N side and hydrogen bonding. All new polymers were characterized by spectral and analytical characterization methods and their sorption data were collected to evaluate their capability as candidates for gas separation applications

Event horizon - Magnifying glass for Planck length physics

An attempt is made to describe the `thermodynamics' of semiclassical spacetime without specifying the detailed `molecular structure' of the quantum spacetime, using the known properties of blackholes. I give detailed arguments, essentially based on the behaviour of quantum systems near the event horizon, which suggest that event horizon acts as a magnifying glass to probe Planck length physics even in those contexts in which the spacetime curvature is arbitrarily low. The quantum state describing a blackhole, in any microscopic description of spacetime, has to possess certain universal form of density of states which can be ascertained from general considerations. Since a blackhole can be formed from the collapse of any physical system with a low energy Hamiltonian H, it is suggested that when such a system collapses to form a blackhole, it should be described by a modified Hamiltonian of the form $H^2_{\rm mod} =A^2 \ln (1+ H^2/A^2)$ where $A^2 \propto E_P^2$.I also show that it is possible to construct several physical systems which have the blackhole density of states and hence will be indistinguishable from a blackhole as far as thermodynamic interactions are concerned. In particular, blackholes can be thought of as one-particle excitations of a class of {\it nonlocal} field theories with the thermodynamics of blackholes arising essentially from the asymptotic form of the dispersion relation satisfied by these excitations. These field theoretic models have correlation functions with a universal short distance behaviour, which translates into the generic behaviour of semiclassical blackholes. Several implications of this paradigm are discussed