Multiwfn is a multifunctional program for wavefunction analysis. Its main functions are: (1) Calculating and visualizing real space function, such as electrostatic potential and electron localization function at point, in a line, in a plane or in a spatial scope. (2) Population analysis. (3) Bond order analysis. (4) Orbital composition analysis. (5) Plot density-of-states and spectrum. (6) Topology analysis for electron density. Some other useful utilities involved in quantum chemistry studies are also provided. The built-in graph module enables the results of wavefunction analysis to be plotted directly or exported to high-quality graphic file. The program interface is very user-friendly and suitable for both research and teaching purpose. The code of Multiwfn is substantially optimized and parallelized. Its efficiency is demonstrated to be significantly higher than related programs with the same functions. Five practical examples involving a wide variety of systems and analysis methods are given to illustrate the usefulness of Multiwfn. The program is free of charge and open-source. Its precompiled file and source codes are available from http://multiwfn.codeplex.com.

Multiwfn: a multifunctional wavefunction analyzer.

To make practical the molecular dynamics simulation of large scale reactive chemical systems (1000s of atoms), we developed ReaxFF, a force field for reactive systems. ReaxFF uses a general relationship between bond distance and bond order on one hand and between bond order and bond energy on the other hand that leads to proper dissociation of bonds to separated atoms. Other valence terms present in the force field (angle and torsion) are defined in terms of the same bond orders so that all these terms go to zero smoothly as bonds break. In addition, ReaxFF has Coulomb and Morse (van der Waals) potentials to describe nonbond interactions between all atoms (no exclusions). These nonbond interactions are shielded at short range so that the Coulomb and van der Waals interactions become constant as Rij → 0. We report here the ReaxFF for hydrocarbons. The parameters were derived from quantum chemical calculations on bond dissociation and reactions of small molecules plus heat of formation and geometry data for...

http://www.wag.caltech.edu/publications/sup/pdf/471.pdf

ReaxFF: A Reactive Force Field for Hydrocarbons

Chlorofluoromethanes are being added to the environment in steadily increasing amounts. These compounds are chemically inert and may remain in the atmosphere for 40–150 years, and concentrations can be expected to reach 10 to 30 times present levels. Photodissociation of the Chlorofluoromethanes in the stratosphere produces significant amounts of chlorine atoms, and leads to the destruction of atmospheric ozone.

Stratospheric sink for chlorofluoromethanes: chlorine atomc-atalysed destruction of ozone

By comparing the ozone depletion potential-weighted anthropogenic emissions of N2O with those of other ozone-depleting substances, we show that N2O emission currently is the single most important ozone-depleting emission and is expected to remain the largest throughout the 21st century. N2O is unregulated by the Montreal Protocol. Limiting future N2O emissions would enhance the recovery of the ozone layer from its depleted state and would also reduce the anthropogenic forcing of the climate system, representing a win-win for both ozone and climate.

http://science.sciencemag.org/content/sci/326/5949/123.full.pdf

Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century

Recent attempts1,2 to consolidate assessments of the effect of human activities on stratospheric ozone (O3) using one-dimensional models for 30° N have suggested that perturbations of total O3 will remain small for at least the next decade. Results from such models are often accepted by default as global estimates3. The inadequacy of this approach is here made evident by observations that the spring values of total O3 in Antarctica have now fallen considerably. The circulation in the lower stratosphere is apparently unchanged, and possible chemical causes must be considered. We suggest that the very low temperatures which prevail from midwinter until several weeks after the spring equinox make the Antarctic stratosphere uniquely sensitive to growth of inorganic chlorine, ClX, primarily by the effect of this growth on the NO2/NO ratio. This, with the height distribution of UV irradiation peculiar to the polar stratosphere, could account for the O3 losses observed.

Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction

Gas Phase Reaction Rate Theory

Although a great deal of attention has been given to the role of water vapor from supersonic transport (SST) exhaust in the stratosphere, oxides of nitrogen from SST exhaust pose a much greater threat to the ozone shield than does an increase in water. The projected increase in stratospheric oxides of nitrogen could reduce the ozone shield by about a factor of 2, thus permitting the harsh radiation below 300 nanometers to permeate the lower atmosphere.

https://science.sciencemag.org/content/sci/173/3996/517.full.pdf

Reduction of stratospheric ozone by nitrogen oxide catalysts from supersonic transport exhaust.

Tunnelling corrections were evaluated for the unsymmetrical Eckart potential for ranges of parameters expected for ordinary chemical reactions at ordinary temperatures.

Tunnelling corrections for unsymmetrical eckart potential energy barriers

Activation Energies from Bond Energies. I. Hydrogen Transfer Reactions

The kinetics of the nitrogen pentoxide catalyzed decomposition of ozone were studied in the dark and with photolytic light absorbed by the NO/sub 3/ radical Ultraviolet, visible, or infrared absorption cross sections were measured for N/sub 2/O/sub 5/, HNO/sub 3/, NO/sub 2/ and NO/sub 3/ The equilibrium constant for N/sub 2/O/sub 5/ reversible NO/sub 2/ + NO/sub 3/ was found to be (molecules cm/sup -3/, 298--329 K) K = (84 +- 18) x 10/sup 26/ exp(-(11180 +- 100)/T) The rate constants for several reactions were measured: (cm/sup 3/ molecule/sup -1/s/sup -1/) 2NO/sub 3/ --> 2NO/sub 2/ + O/sub 2/, g = (85 +- 28) x 10/sup -13/ exp(-(2450 +- 100)/T); O + N/sub 2/O/sub 5/ --> product, m less than or equal to 2 x 10/sup -14/; O + NO/sub 3/ --> O/sub 2/ + NO/sub 2/, n = (10 +- 04) x 10/sup -11/ By combining the equilibrium constant K with literature values of Ke and Kf, rate constants for reactions e and f were evaluated: NO/sub 2/ + NO/sub 3/ --> NO + O/sub 2/ + NO/sub 2/, e = (25 +- 05) x 10/sup -14/ exp(-(1230 +- 100)/T); NO + NO/sub 3/ --> 2NO/sub 2/, f =more » (19 +- 04) x 10/sup -11/ at 297 K At 1 atm total pressure, the photolysis of NO/sub 3/ occurs with a primary quantum yield less than one in the red region of the spectrum The solar photolysis constants at 298 K for the two paths of dissociation are consistent with the following values: NO/sub 3/ + hnu --> NO + O/sub 2/, j/sub 1/ = 0040 +- 002 s/sup -1/; NO/sub 3/ + hnu --> NO/sub 2/ + O, j/sub 2/ = 0099 +- 002 s/sup -1/ The average quantum yield for process two was approximately 077 for light with wavelengths between 470 and 610 nm, and that for process one was about 023 between 470 and 610 nm but only 007 in the strong absorption region between 610 and 670 nm The photolysis constants may be larger at lower total pressures Infrared absorption ascribed to NO/sub 3/ is due to N/sub 2/O/sub 5/; previously reported visible cross sections for NO/sub 3/ were found to be about a factor of 4 too low and are corrected here; previously reported ultraviolet cross sections for N/sub 2/O/sub 5/ are reversed slightly« less

Harold S. Johnston

Papers

Gas Phase Reaction Rate Theory

Reduction of stratospheric ozone by nitrogen oxide catalysts from supersonic transport exhaust.

Tunnelling corrections for unsymmetrical eckart potential energy barriers

Activation Energies from Bond Energies. I. Hydrogen Transfer Reactions

The photochemistry of the nitrate radical and the kinetics of the nitrogen pentoxide-ozone system