TY - JOUR TI - Wetting and nonwetting of molecular films at zero temperature AU - Muirhead, R.J. AU - Dash, J.G. AU - Krim, J. T2 - Physical Review B AB - The wetting characteristics of classical rare gases adsorbed on smooth solid substrates at zero temperature are studied as a function of the molecule-substrate interaction. Comparisons of the relative stabilities of monolayers, bilayers, and trilayers with respect to each other and to the bulk solid phase show a succession of growth regimes with increasing substrate interaction strength relative to molecular pair interactions: nonwetting, incomplete wetting with maximum thicknesses of one layer, incomplete wetting with a mutually commensurate bilayer, and complete wetting. Their order of appearance and the values of substrate strength at crossover boundaries depend sensitively on substrate potential shape, substrate screening of interactions between adsorbate atoms, and the magnitude of the bulk solid energy. Close correspondence with experiment is obtained from Cole-Klein potentials with enhanced first-layer well depths and with substrate screening. This model has a narrow complete wetting region with boundaries at relative substrate strengths near those observed in films on graphite. The complete wetting regime is bounded on the high-strength side by incomplete wetting films consisting of mutually commensurate close-packed bilayers, and on the low-strength side by close-packed monolayers. At still weaker substrate potentials the adsorption is nonwetting. The layer densities of the incompletely wet films are found to be several percent greater than surface planes of the bulk solid, supporting the conjecture that the transition from complete to incomplete, with increasing substrate strength, is driven by structural mismatch between the film and the bulk solid. These features are consistent with observations of light molecular gases on graphite and other surfaces. DA - 1984/// PY - 1984/// DO - 10.1103/PhysRevB.29.5074 VL - 29 IS - 9 SP - 5074-5080 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-24544479341&partnerID=MN8TOARS ER - TY - JOUR TI - Triple-point wetting of light molecular gases on Au(111) surfaces AU - Krim, J. AU - Dash, J.G. AU - Suzanne, J. T2 - Physical Review Letters AB - Wetting characteristics of Ar, Kr, Xe, ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}$, methane, and ethane adsorbed on Au(111) have been determined with a high-frequency microbalance. All gases form incompletely wet films below their bulk triple points and completely wet films above. The transitions to complete wetting are continuous, the maximum thicknesses of the layered films below ${T}_{t}$ varying as ${({T}_{t}\ensuremath{-}T)}^{\ensuremath{-}\frac{1}{3}}$. DA - 1984/// PY - 1984/// DO - 10.1103/PhysRevLett.52.640 VL - 52 IS - 8 SP - 640-643 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-3342994465&partnerID=MN8TOARS ER - TY - JOUR TI - Complete and incomplete wetting of krypton and oxygen on graphite: Reentrant type-2 growth on a scale of substrate strength AU - Bienfait, M. AU - Seguin, J.L. AU - Suzanne, J. AU - Lerner, E. AU - Krim, J. AU - Dash, J.G. T2 - Physical Review B AB - Reflection high-energy electron-diffraction (RHEED) studies of krypton and oxygen films on basal-plane graphite show that the low-temperature mode of growth of Kr is type 1 (complete wetting) whereas that of ${\mathrm{O}}_{2}$ is type 2 (incomplete wetting). The present results extend earlier RHEED measurements on other gases, and indicate the existence of two distinct regimes of incomplete wetting growth separated by a narrow region of complete-wetting growth. These results, together with published work on other films, are analyzed on an improved scale of relative interaction parameters. Arguments are presented to suggest that the mechanisms for incomplete wetting are different in the weak and strong substrate regimes. The present study also shows certain distinct structural relationships between crystallites and layered film in the incomplete wetting growth regime. DA - 1984/// PY - 1984/// DO - 10.1103/PhysRevB.29.983 VL - 29 IS - 2 SP - 983-987 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0001051590&partnerID=MN8TOARS ER - TY - JOUR TI - Elastic and inelastic neutron scattering from Al27at 11, 14, and 17 MeV AU - Whisnant, C. S. AU - Dave, J. H. AU - Gould, C. R. T2 - Physical Review C AB - Fast neutron scattering cross sections have been measured for $^{27}\mathrm{Al}$ using a neutron time-of-flight facility. Angular distributions were measured at angles from 20\ifmmode^\circ\else\textdegree\fi{} to 160\ifmmode^\circ\else\textdegree\fi{} in 5\ifmmode^\circ\else\textdegree\fi{} increments, at incident neutron energies of 11, 14, and 17 MeV. Data are presented for elastic scattering and for inelastic scattering to the sum of the 0.84 and 1.01 MeV states, the 2.21 MeV state, and the sum of the 2.73, 2.98, and 3.00 MeV states. After correcting for compound nucleus effects, the elastic scattering cross sections are well reproduced by the spherical optical model using a linear energy dependence in the real well depth. The inelastic data are interpreted with a coupled channels calculation and the excited core model. DA - 1984/11/1/ PY - 1984/11/1/ DO - 10.1103/physrevc.30.1435 VL - 30 IS - 5 SP - 1435–1441 SN - 0556-2813 UR - http://dx.doi.org/10.1103/physrevc.30.1435 ER - TY - JOUR TI - Measurements of Absolute Collisional Cross Sections at Harvard-Smithsonian CfA AU - Kohl, J.L. AU - Deutsch, L.K. AU - Gardner, L.D. AU - Lafyatis, G.P. AU - Young, A.R. T2 - International Astronomical Union Colloquium AB - The major goal of this research program is to determine, experimentally, accurate absolute cross sections for dielectronic recombination (DR) in multiply and singly charged atomic ions. Our initial measurements of DR in C 3+ are designed to provide a “bench mark” cross section for a simple atomic system. The experiment determines energy averaged DR cross sections for a well defined process involving a specific stabilizing transition. The fields in the region where dielectronic recombination occurs can be made small (≅ 0.25 V/cm) in order to minimize the effect of Stark mixing which is expected to enhance the DR process. We are presently adding the capability to apply known mixing fields up to 5 V/cm in the electron-ion interaction region of our apparatus. DA - 1984/// PY - 1984/// DO - 10.1017/s0252921100085651 VL - 86 SP - 179-182 J2 - International Astronomical Union Colloquium LA - en OP - SN - 0252-9211 UR - http://dx.doi.org/10.1017/s0252921100085651 DB - Crossref ER - TY - JOUR TI - Local density pseudopotential calculations for molecules: O2 and Mo2O2S2(S2)2−2 AU - Bernholc, J. AU - Holzwarth, N. A. W. T2 - The Journal of Chemical Physics AB - We report a development of a self-consistent, local density pseudopotential method for calculation of the electronic properties of large molecules. Angular momentum dependent, first-principles ionic pseudopotentials are used to describe the valence-core interactions. Average correlation effects are included in the local density sense. The wave functions, the charge density and the exchange-correlation potential are expanded in atom-centered Gaussian orbitals of s, p, and d symmetry. These atomic basis sets account for nonspherical (non-muffin tin) effects and are easily transferable to different geometries and other environments. The total energy of the system is accurately evaluated. The method is tested on the O2 molecule and found to give the orbital energies, the equilibrium distance and the vibrational frequency in good agreement with previous all-electron calculations. As the first application to a large system, we have investigated the electronic structure of the Mo2O2S2(S2)2−2 anion. In this anion, the molybdenum atoms are fivefold coordinated: to one oxygen atom, two bridging sulfur atoms, and a molecular S2. From the energy level diagram, the oxygen atoms are found to form approximately triple bonds to the molybdenum atoms, the Mo–S and Mo–S2 bonds being successively weaker. The molybdenum atoms form a single Mo–Mo bond and are formally in the Mo(V) oxidation state. The highest occupied molecular orbitals are, however, the S2 π* orbitals, oriented perpendicular to the Mo-S2 planes and located almost 1 eV above the Mo–Mo bond energy. The lowest unoccupied molecular orbitals are the relatively closely spaced π* antibonding Mo–O, Mo–Mo, and Mo–S2 orbitals. DA - 1984/11// PY - 1984/11// DO - 10.1063/1.448139 VL - 81 IS - 9 SP - 3987-3995 J2 - The Journal of Chemical Physics LA - en OP - SN - 0021-9606 1089-7690 UR - http://dx.doi.org/10.1063/1.448139 DB - Crossref ER - TY - JOUR TI - Convergence of a crossing‐symmetric perturbation series for the four‐point vertex AU - Davis, E. D. AU - Heiss, W. D. T2 - Journal of Mathematical Physics AB - A finite radius of convergence is established for a perturbation expansion of the crossing-symmetric vertex function in a discrete model. DA - 1984/4// PY - 1984/4// DO - 10.1063/1.526227 VL - 25 IS - 4 SP - 812-813 J2 - Journal of Mathematical Physics LA - en OP - SN - 0022-2488 1089-7658 UR - http://dx.doi.org/10.1063/1.526227 DB - Crossref ER - TY - JOUR TI - Electronic structure and identification of deep defects in GaP AU - Scheffler, M. AU - Bernholc, J. AU - Lipari, N. O. AU - Pantelides, S. T. T2 - Physical Review B AB - We report a theoretical study of the Ga vacancy, the P antisite defect (i.e., a P atom occupying a normally Ga site), and carbon impurities at Ga sites. The analysis employs a modified version of the self-consistent Green's-function method that was previously used to describe deep centers in Si. In all three cases, the number, orbital content, and relative energy positions of the localized states can be understood in terms of simple models, as in the case of corresponding centers in Si. In particular, we find that, in all cases, the gap state consists primarily of atomiclike $p$ orbitals centered on the four nearest neighbors, revealing that deviations from $s{p}^{3}$-hybrid character are possible even without any relaxation of the surrounding lattice. In the case of the antisite defect, we find an ${A}_{1}$ bound state in the gap which is consistent with the EPR spectra that led to the identification of the defect. The calculated ionization energies are in agreement with optical data and more recent deep-level-transient-spectroscopy data. In the case of the Ga vacancy, we find a ${T}_{2}$ level in the gap above an ${A}_{1}$ resonance inside the valence bands, and in the case of carbon, we find a deep ${A}_{1}$ level in the gap. These results contradict key assumptions that led to the identification of the NRL-1 EPR signal as the ${V}^{2\ensuremath{-}}$ charge state of the Ga vacancy. More recent experiments redetermined some of the parameters of NRL-1 and reassigned the center to the neutral state of the Ga vacancy. Here, we discuss the interplay between experiment and theory that led to the new identification and describe existing difficulties that limit our ability to construct a detailed model which is consistent with all experiments and with theory. DA - 1984/3/15/ PY - 1984/3/15/ DO - 10.1103/physrevb.29.3269 VL - 29 IS - 6 SP - 3269-3282 J2 - Phys. Rev. B LA - en OP - SN - 0163-1829 UR - http://dx.doi.org/10.1103/physrevb.29.3269 DB - Crossref ER - TY - JOUR TI - THERMODYNAMICALLY CONSISTENT PERTURBATION-THEORY FOR MOLECULAR FLUIDS AU - LADO, F T2 - MOLECULAR PHYSICS AB - New conditions for the reference system in a generalized Andersen-Weeks-Chandler approximation y(12) = g(12) exp [βφ(12)] ≈ y 0(12) are derived which minimize an approximate free energy functional and lead to improved internal thermodynamic consistency for molecular fluids. DA - 1984/// PY - 1984/// DO - 10.1080/00268978400102361 VL - 53 IS - 2 SP - 363-368 SN - 1362-3028 ER - TY - JOUR TI - THERMODYNAMIC CONSISTENCY CONDITIONS FOR THE REFERENCE-HYPERNETTED CHAIN EQUATION WITH ARBITRARY MOLECULAR-POTENTIAL AU - LADO, F T2 - JOURNAL OF CHEMICAL PHYSICS AB - The free energy functional that characterizes the reference-hypernetted chain equation for molecular fluids is variationally minimized, leading to rules for the choice of reference system parameters that guarantee a significant improvement in internal thermodynamic consistency. This work generalizes a successful procedure developed recently for simple fluids. DA - 1984/// PY - 1984/// DO - 10.1063/1.447390 VL - 81 IS - 10 SP - 4592-4593 SN - 0021-9606 ER - TY - JOUR TI - CHOOSING THE REFERENCE SYSTEM FOR LIQUID-STATE PERTURBATION-THEORY AU - LADO, F T2 - MOLECULAR PHYSICS AB - Minimization of an approximate free energy functional yields the Andersen-Weeks-Chandler approximation y(r) ≡ g(r) exp [βφ(r)] ≈ yd(r) along with a new criterion for choosing the reference hard sphere diameter d. The new prescription yields thermodynamic consistency and improved numerical results. DA - 1984/// PY - 1984/// DO - 10.1080/00268978400101621 VL - 52 IS - 4 SP - 871-876 SN - 1362-3028 ER -