• Algorithms for calculating mass-velocity and Darwin relativistic corrections with n-electron explicitly correlated Gaussians with shifted centers

      Stanke, Monika; Palikot, Ewa; Adamowicz, Ludwik; Univ Arizona, Dept Chem & Biochem; Univ Arizona, Dept Phys; Institute of Physics, Faculty of Physics, Astronomy, and Informatics, Nicolaus Copernicus University, ul. Grudzia̧dzka 5, Toruń, PL 87-100, Poland; Institute of Physics, Faculty of Physics, Astronomy, and Informatics, Nicolaus Copernicus University, ul. Grudzia̧dzka 5, Toruń, PL 87-100, Poland; Department of Chemistry and Biochemistry and Department of Physics, University of Arizona, Tucson, Arizona 85721, USA (AMER INST PHYSICS, 2016-05-07)
      Algorithms for calculating the leading mass-velocity (MV) and Darwin (D) relativistic corrections are derived for electronic wave functions expanded in terms of n-electron explicitly correlated Gaussian functions with shifted centers and without pre-exponential angular factors. The algorithms are implemented and tested in calculations of MV and D corrections for several points on the ground-state potential energy curves of the H-2 and LiH molecules. The algorithms are general and can be applied in calculations of systems with an arbitrary number of electrons. Published by AIP Publishing.
    • Eigenstate-specific temperatures in two-level paramagnetic spin lattices

      Masthay, Mark B.; Eads, Calley N.; Johnson, Amber N.; Keil, Robert G.; Miller, Philip; Jones, Ross E.; Mashburn, Joe D.; Fannin, Harry B.; Univ Arizona, Dept Chem & Biochem; Department of Chemistry, University of Dayton, 300 College Park, Dayton, Ohio 45469-2357, USA; et al. (AMER INST PHYSICS, 2017-12-07)
      Increasing interest in the thermodynamics of small and/or isolated systems, in combination with recent observations of negative temperatures of atoms in ultracold optical lattices, has stimulated the need for estimating the conventional, canonical temperature T-c(conv) of systems in equilibrium with heat baths using eigenstate-specific temperatures (ESTs). Four distinct ESTs-continuous canonical, discrete canonical, continuous microcanonical, and discrete microcanonical-are accordingly derived for two-level paramagnetic spin lattices (PSLs) in external magnetic fields. At large N, the four ESTs are intensive, equal to T-c(conv), and obey all four laws of thermodynamics. In contrast, for N < 1000, the ESTs of most PSL eigenstates are non-intensive, differ from T-c(conv), and violate each of the thermodynamic laws. Hence, in spite of their similarities to T-c(conv) at large N, the ESTs are not true thermodynamic temperatures. Even so, each of the ESTs manifests a unique functional dependence on energy which clearly specifies the magnitude and direction of their deviation from T-c(conv); the ESTs are thus good temperature estimators for small PSLs. The thermodynamic uncertainty relation is obeyed only by the ESTs of small canonical PSLs; it is violated by large canonical PSLs and by microcanonical PSLs of any size. The ESTs of population-inverted eigenstates are negative (positive) when calculated using Boltzmann (Gibbs) entropies; the thermodynamic implications of these entropically induced differences in sign are discussed in light of adiabatic invariance of the entropies. Potential applications of the four ESTs to nanothermometers and to systems with long-range interactions are discussed. Published by AIP Publishing.
    • Electron affinity and excited states of methylglyoxal

      Dauletyarov, Yerbolat; Dixon, Andrew R.; Wallace, Adam A.; Sanov, Andrei; Univ Arizona, Dept Chem & Biochem; Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721, USA; Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721, USA; Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721, USA; Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721, USA (AMER INST PHYSICS, 2017-07-07)
      Using photoelectron imaging spectroscopy, we characterized the anion of methylglyoxal (X(2)A" electronic state) and three lowest electronic states of the neutral methylglyoxal molecule: the closed-shell singlet ground state (X(1)A'), the lowest triplet state (a(3)A"), and the open-shell singlet state (A(1)A"). The adiabatic electron affinity (EA) of the ground state, EA(X(1)A') = 0.87(1) eV, spectroscopically determined for the first time, compares to 1.10(2) eV for unsubstituted glyoxal. The EAs (adiabatic attachment energies) of two excited states of methylglyoxal were also determined: EA(a(3)A") = 3.27(2) eV and EA(A(1)A") = 3.614(9) eV. The photodetachment of the anion to each of these two states produces the neutral species near the respective structural equilibria; hence, the a(3)A" <- X(2)A" and A(1)A" <- X(2)A" photodetachment transitions are dominated by intense peaks at their respective origins. The lowest-energy photodetachment transition, on the other hand, involves significant geometry relaxation in the X(1)A' state, which corresponds to a 60 degrees internal rotation of the methyl group, compared to the anion structure. Accordingly, the X(1)A' <- X(2)A" transition is characterized as a broad, congested band, whose vertical detachment energy, VDE = 1.20(4) eV, significantly exceeds the adiabatic EA. The experimental results are in excellent agreement with the ab initio predictions using several equation-of-motion methodologies, combined with coupled-cluster theory. Published by AIP Publishing.
    • Examining transition metal hydrosulfides: The pure rotational spectrum of ZnSH (X̃2A′)

      Bucchino, M. P.; Adande, G. R.; Halfen, D. T.; Ziurys, L. M.; Univ Arizona, Dept Chem & Biochem (AMER INST PHYSICS, 2017-10-21)
      The pure rotational spectrum of the ZnSH ((X) over tilde (2)A') radical has been measured using millimeter-wave direct absorption and Fourier transform microwave (FTMW) methods across the frequency range 18-468 GHz. This work is the first gas-phase detection of ZnSH by any spectroscopic technique. Spectra of the (ZnSH)-Zn-66, (ZnSH)-Zn-68, and (ZnSD)-Zn-64 isotopologues were also recorded. In the mm-wave study, ZnSH was synthesized in a DC discharge by the reaction of zinc vapor, generated by a Broidatype oven, with H2S; for FTMW measurements, the radical was made in a supersonic jet expansion by the same reactants but utilizing a discharge-assisted laser ablation source. Between 7 and 9 rotational transitions were recorded for each isotopologue. Asymmetry components with K-a = 0 through 6 were typically measured in the mm-wave region, each split into spin-rotation doublets. In the FTMW spectra, hyperfine interactions were also resolved, arising from the hydrogen or deuterium nuclear spins of I = 1/2 or I = 1, respectively. The data were analyzed using an asymmetric top Hamiltonian, and rotational, spin-rotation, and magnetic hyperfine parameters were determined for ZnSH, as well as the quadrupole coupling constant for ZnSD. The observed spectra clearly indicate that ZnSH has a bent geometry. The r(m)((1)) structure was determined to be r(Zn-S) = 2.213(5) angstrom, r(S-H) = 1.351(3) angstrom, and theta(Zn-S-H) = 90.6(1)degrees, suggesting that the bonding occurs primarily through sulfur p orbitals, analogous to H2S. The hyperfine constants indicate that the unpaired electron in ZnSH primarily resides on the zinc nucleus. Published by AIP Publishing.
    • Millimeter-wave spectroscopy of CrC (X3Σ−) and CrCCH (X̃ 6Σ+): Examining the chromium-carbon bond

      Min, J.; Ziurys, L. M.; Univ Arizona, Steward Observ, Dept Astron, Dept Chem & Biochem; Department of Chemistry and Biochemistry, Department of Astronomy, Steward Observatory, 933 North Cherry Avenue, University of Arizona, Tucson, Arizona 85721, USA; Department of Chemistry and Biochemistry, Department of Astronomy, Steward Observatory, 933 North Cherry Avenue, University of Arizona, Tucson, Arizona 85721, USA (AMER INST PHYSICS, 2016-05-14)
      Pure rotational spectroscopy of the CrC (X-3 Sigma(-)) and CrCCH ((X) over tilde (6)Sigma(+)) radicals has been conducted using millimeter/sub-millimeter direct absorption methods in the frequency range 225-585 GHz. These species were created in an AC discharge of Cr(CO)(6) and either methane or acetylene, diluted in argon. Spectra of the CrCCD were also recorded for the first time using deuterated acetylene as the carbon precursor. Seven rotational transitions of CrC were measured, each consisting of three widely spaced, fine structure components, arising from spin-spin and spin-rotation interactions. Eleven rotational transitions were recorded for CrCCH and five for CrCCD; each transition in these cases was composed of a distinct fine structure sextet. These measurements confirm the respective (3)Sigma(-) and (6)Sigma(+) ground electronic states of these radicals, as indicated from optical studies. The data were analyzed using a Hund's case (b) Hamiltonian, and rotational, spin-spin, and spin-rotation constants have been accurately determined for all three species. The spectroscopic parameters for CrC were significantly revised from previous optical work, while those for CrCCH are in excellent agreement; completely new constants were established for CrCCD. The chromium-carbon bond length for CrC was calculated to be 1.631 angstrom, while that in CrCCH was found to be r(Cr-C) = 1.993 angstrom - significantly longer. This result suggests that a single Cr-C bond is present in CrCCH, preserving the acetylenic structure of the ligand, while a triple bond exists in CrC. Analysis of the spin constants suggests that CrC has a nearby excited (1)Sigma(+) state lying similar to 16 900 cm(-1) higher in energy, and CrCCH has a (6)Pi excited state with E similar to 4800 cm(-1). Published by AIP Publishing.
    • A molecular dynamics study of the role of molecular water on the structure and mechanics of amorphous geopolymer binders

      Sadat, Mohammad Rafat; Bringuier, Stefan; Asaduzzaman, Abu; Muralidharan, Krishna; Zhang, Lianyang; Univ Arizona, Dept Civil Engn & Engn Mech; Univ Arizona, Dept Mat Sci & Engn (AMER INST PHYSICS, 2016-10-07)
      In this paper, molecular dynamics simulations are used to study the effect of molecular water and composition (Si/Al ratio) on the structure and mechanical properties of fully polymerized amorphous sodium aluminosilicate geopolymer binders. The X-ray pair distribution function for the simulated geopolymer binder phase showed good agreement with the experimentally determined structure in terms of bond lengths of the various atomic pairs. The elastic constants and ultimate tensile strength of the geopolymer binders were calculated as a function of water content and Si/Al ratio; while increasing the Si/Al ratio from one to three led to an increase in the respective values of the elastic stiffness and tensile strength, for a given Si/Al ratio, increasing the water content decreased the stiffness and strength of the binder phase. An atomic-scale analysis showed a direct correlation between water content and diffusion of alkali ions, resulting in the weakening of the AlO4 tetrahedral structure due to the migration of charge balancing alkali ions away from the tetrahedra, ultimately leading to failure. In the presence of water molecules, the diffusion behavior of alkali cations was found to be particularly anomalous, showing dynamic heterogeneity. This paper, for the first time, proves the efficacy of atomistic simulations for understanding the effect of water in geopolymer binders and can thus serve as a useful design tool for optimizing composition of geopolymers with improved mechanical properties. Published by AIP Publishing.
    • Orbit-orbit relativistic correction calculated with all-electron molecular explicitly correlated Gaussians

      Stanke, Monika; Palikot, Ewa; Kȩdziera, Dariusz; Adamowicz, Ludwik; Univ Arizona, Dept Chem & Biochem; Univ Arizona, Dept Phys; Institute of Physics, Faculty of Physics, Astronomy, and Informatics, Nicolaus Copernicus University in Torun, ul. Grudzia̧dzka 5, Toruń PL 87-100, Poland; Institute of Physics, Faculty of Physics, Astronomy, and Informatics, Nicolaus Copernicus University in Torun, ul. Grudzia̧dzka 5, Toruń PL 87-100, Poland; Faculty of Chemistry, Nicolaus Copernicus University, ul. Gagarina 7, Toruń PL 87-100, Poland; Department of Chemistry and Biochemistry and Department of Physics, University of Arizona, Tucson, Arizona 85721, USA andInterdisciplinary Center for Modern Technologies, Nicolaus Copernicus University, ul. Wileńska 4, Toruń PL 87-100, Poland (AMER INST PHYSICS, 2016-12-14)
      An algorithm for calculating the first-order electronic orbit-orbit magnetic interaction correction for an electronic wave function expanded in terms of all-electron explicitly correlated molecular Gaussian (ECG) functions with shifted centers is derived and implemented. The algorithm is tested in calculations concerning the H-2 molecule. It is also applied in calculations for LiH and H-3(+) molecular systems. The implementation completes our work on the leading relativistic correction for ECGs and paves the way for very accurate ECG calculations of ground and excited potential energy surfaces (PESs) of small molecules with two and more nuclei and two and more electrons, such as HeH, H-3(+), HeH2+, and LiH2+. The PESs will be used to determine rovibrational spectra of the systems. Published by AIP Publishing.