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Displaying 1 - 21 of 21

To Predict Vibrational Spectra, Are Anharmonic Calculations Worthwhile?

January 22, 2013
Author(s)
Ruth L. Jacobsen, Karl K. Irikura, Russell D. Johnson III, Raghu N. Kacker
Anharmonic calculations using vibrational perturbation theory are known to provide near-spectroscopic accuracy when combined with high-level ab initio potential energy functions. However, performance with economical, popular electronic structure methods is

Scaling Factors and Uncertainties for ab Initio Anharmonic Vibrational Frequencies

August 21, 2009
Author(s)
Russell D. Johnson III, Karl K. Irikura, Raghu N. Kacker, Ruediger Kessel
To predict the vibrational spectra of molecules, ab initio calculations are often used to compute harmonic frequencies, which are usually scaled by empirical factors as an approximate correction for errors in the force constants and for anharmonic effects

Uncertainties in Scaling Factors for ab Initio Vibrational Zero-Point Energies

March 21, 2009
Author(s)
Karl K. Irikura, Russell D. Johnson III, Raghu N. Kacker, Ruediger Kessel
Vibrational zero-point energies (ZPEs) determined from ab initio calculations are often scaled by empirical factors. An empirical scaling factor partially compensates for the effects arising from vibrational anharmonicity and incomplete treatment of

Thermodynamic properties of methylquinolines: Experimental results for 2,6-dimethylquinoline and mutual validation between experiments and computational methods for methylquinolines

May 1, 2007
Author(s)
Robert D. Chirico, Russell D. Johnson III, William Steele
Measurements leading to the calculation of the standard thermodynamic properties for gaseous 2,6-dimethylquinoline (Chemical Abstracts registry number [877-43-0]) are reported. Experimental methods included adiabatic heat-capacity calorimetry, vibrating

Is NO 3 Formed During the Decomposition of Nitramine Explosives?

December 21, 2006
Author(s)
Karl K. Irikura, Russell D. Johnson III
Quantum chemistry calculations reveal that it is both thermodynamically and kinetically reasonable to produce NO3 (nitrate radical) during the thermal decomposition of RDX (1,3,5-trinitrohexahydro-s-triazine) and other nitramines. However, experimental

Uncertainties in Scaling Factors for ab Initio Vibrational Frequencies

September 1, 2005
Author(s)
Karl K. Irikura, Russell D. Johnson III, Raghu N. Kacker
Vibrational frequencies determined from ab initio calculations are often scaled by empirical factors. An empirical scaling factor partially compensates for the errors arising from vibrational anharmonicity and incomplete treatment of electron correlation

The Industrial Fluid Properties Simulation Challenge

March 1, 2004
Author(s)
Raymond D. Mountain, F Case, Anne M. Chaka, Daniel G. Friend, David Frurip, Russell D. Johnson III, J Golab, P Kolar, J Moore, J Olson, Martin Schiller, J Storer
This poster describes the results, activities, and philosophy of the Industrial Fluids Simulation Challenge. The recently completed open competition challenged practitioners of molecular simulation to calculate accurate physical properties for pure

NIST 101. Computational Chemistry Comparison and Benchmark Database

November 1, 1999
Author(s)
Russell D. Johnson III
The CCCBDB is a collection of experimental and theoretical thermochemical properties for 580 neutral gas-phase species. The goal of the database/website is to provide a benchmark set of molecules and reactions for the evaluation of ab initio computational

Photoionization Efficiency Spectrum And Ionization Energy of Obro

November 1, 1999
Author(s)
R P. Thorn, L J. Stief, T J. Buckley, Russell D. Johnson III, P S. Monks, R B. Klemm
The photoionization efficiency (PIE) spectrum of OBrO was measured over the wavelength range [Lambda] = 86 - 126 nm by using a discharge flow-photoionization mass spectrometer (DF-PIMS) apparatus coupled to a VUV synchrotron radiation source. Bromine

Predicting Unexpected Chemical Reactions by Isopotential Searching

October 1, 1999
Author(s)
Karl K. Irikura, Russell D. Johnson III
The reactions of a chemical system are dictated by the corresponding potential energy surface (PES). Since reasonably accurate PESs are now available from quantum chemical calculations, a great deal of chemistry can, in principle, be predicted using

Sicklist Database

October 1, 1999
Author(s)
Russell D. Johnson III
This is a database of problems that arise from using a particular ab initio computational method with a particular molecule. It is intended to serve as a guide to prevent people from wasting resources struggling with known problems and to offer solutions