Simulation Of Electronic And Geometric Degrees Of Freedom Using A Kink-Based Path Integral Formulation: Application To Molecular Systems, Randall Hall
Oct 2015
Simulation Of Electronic And Geometric Degrees Of Freedom Using A Kink-Based Path Integral Formulation: Application To Molecular Systems, Randall Hall
Randall W. Hall
A kink-based path integral method, previously applied to atomic systems, is modified and used to study molecular systems. The method allows the simultaneous evolution of atomic and electronic degrees of freedom. Results for CH4, NH3, and H2O demonstrate this method to be accurate for both geometries and energies. Comparison with DFT and MP2 level calculations show the path integral approach to produce energies in close agreement with MP2 energies and geometries in close agreement with both DFT and MP2 results.
Microscopic Theory Of Network Glasses, Randall Hall, Peter Wolynes
Oct 2015
Microscopic Theory Of Network Glasses, Randall Hall, Peter Wolynes
Randall W. Hall
A theory of the glass transition of network liquids is developed using self-consistent phonon and liquid state approaches. The dynamical transition and entropy crisis characteristic of random first-order transitions are mapped as a function of the degree of bonding and density. Using a scaling relation for a soft-core model to crudely translate the densities into temperatures, theory predicts that the ratio of the dynamical transition temperature to the laboratory transition temperature rises as the degree of bonding increases, while the Kauzmann temperature falls explaining why highly coordinated liquids are “strong” while van der Waals liquids without coordination are “fragile.”
The Sign Learning Kink (Silk) Based Quantum Monte Carlo (Qmc), Xiaoyao Ma, Frank Loffler, Randall W. Hall, Karol Kowalski, Mark Jarrell, Juana Moreno
Dec 2014
The Sign Learning Kink (Silk) Based Quantum Monte Carlo (Qmc), Xiaoyao Ma, Frank Loffler, Randall W. Hall, Karol Kowalski, Mark Jarrell, Juana Moreno
Randall W. Hall
Purpose
The Sign Learning Kink (SiLK) based Quantum Monte Carlo (QMC) method is based on Feynman's path integral formulation of quantum mechanics, and can reduce the minus sign problem when calculating energies in atomic and molecular systems. The code requires as input the one and two electron integrals, which usually are computed using the NWChem package. Example input files are distributed with this package. The code also requires an parameter file, specifying run-time parameters such as input/output directories, or specific code parameters. For all example inputs a corresponding parameter file is distributed as well.
Systems
The code has been tuned …
Density Functional Calculation Of The Structure And Electronic Properties Of CuNON (N = 1−8) Clusters, Gyun-Tack Bae, Randall W. Hall, Barry Dellinger
Dec 2010
Density Functional Calculation Of The Structure And Electronic Properties Of CuNON (N = 1−8) Clusters, Gyun-Tack Bae, Randall W. Hall, Barry Dellinger
Randall W. Hall
Ab initio simulations and calculations were used to study the structures and stabilities of copper oxide clusters, CunOn (n = 1−8). The lowest energy structures of neutral and charged copper oxide clusters were determined using primarily the B3LYP/LANL2DZ model chemistry. For n ≥ 4, the clusters are nonplanar. Selected electronic properties including atomization energies, ionization energies, electron affinities, and Bader charges were calculated and examined as a function of n.
Density Functional Calculation Of The Structure And Electronic Properties Of CuNON (N = 1−4) Clusters, Gyun-Tack Bae, Randall W. Hall
Dec 2008
Density Functional Calculation Of The Structure And Electronic Properties Of CuNON (N = 1−4) Clusters, Gyun-Tack Bae, Randall W. Hall
Randall W. Hall
The formation, stability, and reactivity of chlorinated phenoxyl radicials was studied using ab initio methods. All 19 congeners from mono- to penta-chlorinated species were considered. The radical species are formed in combustion reactions via unimolecular scission of the phenoxyl-hydrogen bond or hydrogen atom abstraction by hydrogen atom or hydroxyl radical. The resulting radicals are stable with respect to unimolecular decomposition and reaction with molecular oxygen is relatively slow. Activation energies are similar to those of the phenoxyl radical for both the decomposition pathway and the reaction with molecular oxygen at the more reactive para-position. Calculations were performed with the model …
Ab Initio Study Of The Formation And Degradation Reactions Of Chlorinated Phenols, Cheri A. Mcferrin, Randall W. Hall, Barry Dellinger
Dec 2008
Ab Initio Study Of The Formation And Degradation Reactions Of Chlorinated Phenols, Cheri A. Mcferrin, Randall W. Hall, Barry Dellinger
Randall W. Hall
The formation, stability, and reactivity of chlorinated phenoxyl radicials was studied usingab initio methods. All 19 congeners from mono- to penta-chlorinated species were considered. The radical species are formed in combustion reactions via unimolecular scission of the phenoxyl-hydrogen bond or hydrogen atom abstraction by hydrogen atom or hydroxyl radical. The resulting radicals are stable with respect to unimolecular decomposition and reaction with molecular oxygen is relatively slow. Activation energies are similar to those of the phenoxyl radical for both the decomposition pathway and the reaction with molecular oxygen at the more reactive para-position. Calculations were performed with the …
Intermolecular Forces And The Glass Transition, Randall W. Hall, Peter G. Wolynes
Dec 2007
Intermolecular Forces And The Glass Transition, Randall W. Hall, Peter G. Wolynes
Randall W. Hall
Random first-order transition theory is used to determine the role of attractive and repulsive interactions in the dynamics of supercooled liquids. Self-consistent phonon theory, an approximate mean field treatment consistent with random first-order transition theory, is used to treat individual glassy configurations, whereas the liquid phase is treated using common liquid-state approximations. Free energies are calculated using liquid-state perturbation theory. The transition temperature,, the temperature where the onset of activated behavior is predicted by mean field theory; the lower crossover temperature,, where barrierless motions actually occur through fractal or stringy motions (corresponding to the phenomenological mode coupling transition temperature); and, …
Formation And Stabilization Of Persistent Free Radicals, Barry Dellinger, Slawomir Lomnicki, Lavrent Khachatryan, Zofia Maskos, Randall W. Hall, Julien Adounkpe, Cheri Mcferrin, Hieu Truong
Aug 2006
Formation And Stabilization Of Persistent Free Radicals, Barry Dellinger, Slawomir Lomnicki, Lavrent Khachatryan, Zofia Maskos, Randall W. Hall, Julien Adounkpe, Cheri Mcferrin, Hieu Truong
Randall W. Hall
We demonstrate that stable and relatively unreactive “environmentally persistent free radicals (PFRs)” can be readily formed in the post-flame and cool-zone regions of combustion systems and other thermal processes. These resonance-stabilized radicals, including semiquinones, phenoxyls, and cyclopentadienyls, can be formed by the thermal decomposition of molecular precursors including catechols, hydroquinones and phenols. Association with the surfaces of fine particles imparts additional stabilization to these radicals such that they can persist almost indefinitely in the environment. A mechanism of chemisorption and electron transfer from the molecular adsorbate to a redox-active transition metal or other receptor is shown through experiment, and supported …
Hall And Wolynes Reply [Reply To Comment On ‘‘Microscopic Theory Of Network Glasses’’], Randall W. Hall, Peter G. Wolynes
Oct 2003
Hall And Wolynes Reply [Reply To Comment On ‘‘Microscopic Theory Of Network Glasses’’], Randall W. Hall, Peter G. Wolynes
Randall W. Hall
In a Comment on our recent paper on network glasses (Phys. Rev. Lett., 2003, 90, 085505), Micoulaut and Boolchand (MB) compare our predictions on glass transitions in network systems for the ratios of the transition temperatures TA/TG and TK/TG with experimental data. They claim significant differences between experiment and theory are seen and claim the lack of agreement is due to flaws in our theory. Their comparison of TA/TG is incorrect as they do not measure the same quantity that our theory predicts. The TK/TG comparison shows remarkable agreement between theory and experiment.
