We develop a proper nonempirical spin-density formalism for the van der Waals density functional (vdW-DF) method. We show that this generalization, termed svdW-DF, is firmly rooted in the single-particle nature of exchange and we test it on a range of spin systems. We investigate in detail the role of spin in the nonlocal-correlation driven adsorption of H2 and CO2 in the linear magnets Mn-MOF74, Fe-MOF74, Co-MOF74, and Ni-MOF74. In all cases, we find that spin plays a significant role during the adsorption process despite the general weakness of the molecular-magnetic responses. The case of CO2 adsorption in Ni-MOF74 is particularly interesting, as the inclusion of spin effects results in an increased attraction, opposite to what the diamagnetic nature of CO2 would suggest. We explain this counter-intuitive result, tracking the behavior to a coincidental hybridization of the O p states with the Ni d states in the down-spin channel. More generally, by providing insight on nonlocal correlation in concert with spin effects, our nonempirical svdW-DF method opens the door for a deeper understanding of weak nonlocal magnetic interactions. The modular building-block nature of metal organic frameworks (MOFs) and their extraordinary affinity for adsorption of small molecules make these nano-porous materials ideal for technologically important applications. MOFs are used, for example, for gas storage and sequestration [1][2][3][4][5], catalysis [6,7], polymerization [8,9], luminescence [10,11], non-linear optics [12], magnetic networks [13], targeted drug delivery [14], multiferroics [15][16][17], and sensing [18][19][20][21]. The design of novel MOFs with improved properties requires insight into the molecule/MOF interaction. The large unit cells and periodic nature of MOFs make density functional theory (DFT) the prospective tool for a theory exploration. However, both the adsorbate molecule and the MOF's metal centers can carry spin, giving rise to complex magnetic interactions and a molecular-spin response. It is thus crucial that DFT can reliably capture van der Waals (vdW) forces-which govern adsorption in MOFs-in concert with spin effects.Concerning the former, the last decade witnessed the development of DFT descriptions for these forces [22]. Here, the vdW-DF versions [23][24][25][26] stand out by being nonempirical exchange-correlation functionals that are systematic and truly nonlocal extensions beyond LDA [27] and GGA [28] in the electron-gas tradition [22,29,30]. Subsequent developments include variants which differ by their choice of the semi-local exchange [31][32][33][34][35] and related nonlocal correlation functionals that rely on optimizing parameters [36][37][38]. The vdW-DF method and relatives have been successfully applied to numerous materials in general [22,29,39], and to smallmolecule adsorption in MOFs in particular [4,5,[40][41][42][43][44][45][46].Concerning the spin effects, however, a systematic description within the vdW-DF framework is still missing. Such effects can play important roles ...

The theoretical description of sparse matter attracts much interest, in particular for those ground-state properties that can be described by density functional theory. One proposed approach, the van der Waals density functional (vdW-DF) method, rests on strong physical foundations and offers simple yet accurate and robust functionals. A very recent functional within this method called vdW-DF-cx [K. Berland and P. Hyldgaard, Phys. Rev. B 89, 035412 (2014)] stands out in its attempt to use an exchange energy derived from the same plasmon-based theory from which the nonlocal correlation energy was derived. Encouraged by its good performance for solids, layered materials, and aromatic molecules, we apply it to several systems that are characterized by competing interactions. These include the ferroelectric response in PbTiO3, the adsorption of small molecules within metal-organic frameworks, the graphite/diamond phase transition, and the adsorption of an aromatic-molecule on the Ag(111) surface. Our results indicate that vdW-DF-cx is overall well suited to tackle these challenging systems. In addition to being a competitive density functional for sparse matter, the vdW-DF-cx construction presents a more robust general-purpose functional that could be applied to a range of materials problems with a variety of competing interactions.

Using high-throughput screening coupled with state-of-the-art van der Waals density functional theory, we investigate the adsorption properties of four important molecules, H2, CO2, CH4, and H2O in MOF-74-M with M = Be, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Zr, Nb, Ru, Rh, Pd, La, W, Os, Ir, and Pt. We show that high-throughput techniques can aid in speeding up the development and refinement of effective materials for hydrogen storage, carbon capture, and gas separation. The exploration of the configurational adsorption space allows us to extract crucial information concerning, for example, the competition of water with CO2 for the adsorption "pockets." We find that only a few noble metals-Rh, Pd, Os, Ir, and Pt-favor the adsorption of CO2 and hence are potential candidates for effective carbon-capture materials. Our findings further reveal significant differences in the binding characteristics of H2, CO2, CH4, and H2O within the MOF structure, indicating that molecular blends can be successfully separated by these nano-porous materials.

On-road vehicular emissions contribute to the formation of fine particulate matter and ozone which can lead to increased adverse health outcomes near the emission source and downwind. In this study, we present a transportation-specific modeling platform utilizing the community multiscale air quality model (CMAQ) with the decoupled direct method (DDM) to estimate the air quality and health impacts of on-road vehicular emissions from five vehicles classes; light-duty autos, light-duty trucks (LDT), medium-duty trucks, heavy-duty trucks (HDT), and buses (BUS), on PM2.5 and O3 concentrations at a 12 × 12 kilometer scale for 12 states and Washington D.C. as well as four large metropolitan statistical areas in the Northeast and Mid-Atlantic U.S. in 2016. CMAQ-DDM allows for the quantification of sensitivities from individual precursor emissions (NO X , SO2, NH3, volatile organic compounds, and PM2.5) in each state to pollution levels and health effects in downwind states. In the region we considered, LDT are responsible for the most PM2.5-attributable premature mortalities at 1234 with 46% and 26% of those mortalities from directly emitted primary particulate matter and NH3, respectively; and O3-attributable premature mortalities at 1129 with 80% of those mortalities from NO X emissions. Based on a detailed source-receptor matrix of sensitivities with subsequent monetization of damages that we computed, we find that the largest damages-per-ton estimate is approximately $4 million per ton of directly emitted primary particulate matter from BUS in the New York-Newark-Jersey City metropolitan statistical area. We find that on-road vehicular NH3 emissions are the second largest contributor to PM2.5 concentrations and health impacts in the study region, and that reducing 1 ton of NH3 emissions from LDT is ∼75 times and from HDT is ∼90 times greater in terms of damages reductions than a 1 ton reduction of NO X . By quantifying the impacts by each combination of source region, vehicle class, and emissions precursor this study allows for a comprehensive understanding of the largest vehicular sources of air quality-related premature mortalities in a heavily populated part of the U.S. and can inform future policies aimed at reducing those impacts.

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