The energies of the solid reactants in the lead-acid battery are calculated ab initio using two different basis sets at non-relativistic, scalar relativistic, and fully relativistic levels, and using several exchange-correlation potentials. The average calculated standard voltage is 2.13 V, compared with the experimental value of 2.11 V. All calculations agree in that 1.7-1.8 V of this standard voltage arise from relativistic effects, mainly from PbO2 but also from PbSO4. PACS numbers: 82.47.Cb,82.60.Cx,31.15.ae,31.15.aj,31.15.es Keywords: lead, lead battery, relativity, relativistic effectsThe lead battery is an essential part of cars, and has numerous other applications. This well-known invention is now 150 years old [1,2]. About 75% of the World lead production and a turnover of about 30 billion USD are due to these batteries. Although there are electrochemical simulations starting from the given thermodynamical data[3, 4], we are not aware of any ab initio ones for the lead battery. This is in stark contrast to other rechargeable batteries, such as the modern lithium-ion based systems, where they abound. The problem is difficult enough to be a theoretical challenge, and there is the additional fascination that, Pb being a heavy-element, relativistic effects on its compounds could play an important role, as qualitatively found a long time ago [5][6][7][8]. For metallic lead, see [9][10][11].The discharge reaction of the lead-acid cell isThe electronic structures of both and β-PbO 2 [15-17] have been theoretically studied earlier. Especially, the metallic conductivity of the β-PbO 2 , making the large currents possible, was shown to be an impurity, conduction-band effect, attributed to donor impurities at oxygen sites [16][17][18][19]. The alloying of the Pb electrode is also important in practice, but is not discussed here, because the minute amounts of other elements do not affect the EMF of the cell.The construction of the lead-acid battery[20] has a positive lead dioxide electrode, a negative electrode of metallic lead, and a sulfuric acid electrolyte. The discharge reaction between a Pb(IV) and a Pb(0) produces 2 Pb(II), in form of solid PbSO 4 . The experimental thermodynamics of the reaction are well-known [21].The three solids can be treated with existing solid-state theories, such as density functional theory (DFT), because the bonding mechanism in the investigated species is dominated by covalent interactions where DFT is expected to provide reliable results. Adequately simulating the liquid phase in multiple relativistic regimes is beyond current state of the art, however. We avoid this problem by introducing the known energy ∆E(2) for the experimental reactionWe can use this empirical relationship because only light elements and only S(VI) occur in eq. (2), whose contribution to relativistic effects are small. Combining the equations (1) and (2) givesThe voltages for the lead-acid battery reaction may then be calculated from the reaction energieswhere we use calculated ∆E(3) values and experimenta...

Recent high-pressure experiments conducted on xenon difluoride (XeF(2)) suggested that this compound undergoes several phase transitions up to 100 GPa, becoming metallic above 70 GPa. In this theoretical study, in contrast to experiment, we find that the ambient pressure molecular structure of xenon difluoride, of I4/mmm symmetry, remains the most stable one up to 105 GPa. In our computations, the structures suggested from experiment have either much higher enthalpies than the I4/mmm structure or converge to that structure upon geometry optimization. We discuss these discrepancies between experiment and calculation and point to an alternative interpretation of the measured cell vectors of XeF(2) at high pressure. At pressures exceeding those studied experimentally, above 105 GPa, the I4/mmm structure transforms to one of Pnma symmetry. The Pnma phase contains bent FXeF molecules, with unequal Xe-F distances, and begins to bring other fluorines into the coordination sphere of the Xe. Further compression of this structure up to 200 GPa essentially results in self-dissociation of XeF(2) into an ionic solid (i.e., [XeF](+)F(-)), similar to what is observed for nitrous oxide (N(2)O) at high pressure.

High-precision calculations are reported for the title series with M=Cu, Ag, Au, using CCSD(T) with the latest pseudopotentials and basis sets up to cc-pVQZ. The bond lengths for M=Cu, Ag, Au agree with experiment within better than 1 pm. The role of deep-core excitations is studied. The second-order spin-orbit effects are evaluated at the density functional theory level, including M=Rg. A qualitative bonding analysis suggests multiple M-C bonding. The calculated vibrational frequencies are expected to be more accurate than the available experimental estimates. The M-C bond lengths obey Cu

Modern ab initio calculations predict ionic and superionic states in highly compressed water and ammonia. The prediction apparently contradicts state-of-the-art experimentally established phase diagrams overwhelmingly dominated by molecular phases. Here we present experimental evidence that the threshold pressure of B120 GPa induces in molecular ammonia the process of autoionization to yet experimentally unknown ionic compoundammonium amide. Our supplementary theoretical simulations provide valuable insight into the mechanism of autoionization showing no hydrogen bond symmetrization along the transformation path, a remarkably small energy barrier between competing phases and the impact of structural rearrangement contribution on the overall conversion rate. This discovery is bridging theory and experiment thus opening new possibilities for studying molecular interactions in hydrogen-bonded systems. Experimental knowledge on this novel ionic phase of ammonia also provides strong motivation for reconsideration of the theory of molecular ice layers formation and dynamics in giant gas planets.

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An initial observation of the formation of WH under pressure from W gaskets surrounding hydrogen in diamond anvil cells led to a theoretical study of tungsten hydride phases. At P = 1 atm no stoichiometry is found to be stable with respect to separation into the elements, but as the pressure is raised WH(n) (n = 1-6, 8) stoichiometries are metastable or stable. WH and WH(4) are calculated to be stable at P > 15 GPa, WH(2) becomes stable at P > 100 GPa and WH(6) at P > 150 GPa. In agreement with experiment, the structure computed for WH is anti-NiAs. WH(2) shares with WH a hexagonal arrangement of tungsten atoms, with hydrogen atoms occupying octahedral and tetrahedral holes. For WH(4) the W atoms are in a distorted fcc arrangement. As the number of hydrogens rises, the coordination of W by H increases correspondingly, leading to a twelve-coordinated W in WH(6). In WH(8) H(2) units also develop. All of the hydrides considered should be metallic at high pressure, though the Fermi levels of WH(4) and WH(6) lie in a deep pseudogap. Prodded by these theoretical studies, experiments were then undertaken to seek phases other than WH, exploring a variety of experimental conditions that would favor further reaction. Though a better preparation and characterization of WH resulted, no higher hydrides have as yet been found.

In all of its known connections nitrogen retains a valence shell electron count of eight therefore satisfying the golden rule of chemistry - the octet rule. Despite the diversity of nitrogen chemistry (with oxidation states ranging from + 5 to −3), and despite numerous efforts, compounds containing nitrogen with a higher electron count (hypervalent nitrogen) remain elusive and are yet to be synthesized. One possible route leading to nitrogen’s hypervalency is the formation of a chemical moiety containing pentavalent nitrogen atoms coordinated by more than four substituents. Here, we present theoretical evidence that a salt containing hexacoordinated nitrogen(V), in the form of an NF6− anion, could be synthesized at a modest pressure of 40 GPa (=400 kbar) via spontaneous oxidation of NF3 by F2. Our results indicate that the synthesis of a new class of compounds containing hypervalent nitrogen is within reach of current high-pressure experimental techniques.