Accession Number : ADA245055


Title :   A Priori Calculations of Thermodynamic Functions


Descriptive Note : Doctoral thesis,


Corporate Author : TEXAS UNIV AT AUSTIN


Personal Author(s) : Cordell, Floyd R


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a245055.pdf


Report Date : Dec 1991


Pagination or Media Count : 223


Abstract : A method for calculating a priori thermodynamic functions (specific heat, entropy, free energy, and enthalpy) from a combination of single determinant ab initio calculations employing the 4-21NO basis and experimental data is developed and validated. An estimate of the re geometry is determined by empirically correcting the optimized 4-21NO ab initio geometry with formulae derived from carefully selected experimental re rs and rg geometries for errors caused by basis set truncation and neglect of electron correlation. The r(e) geometry is then used as the reference geometry for the calculation of the ab initio force field by the finite difference method. The Scaled Quantum Mechanical force field is calculated from the ab initio force field using a standard set of scale factors. Fundamental vibration frequencies derived from Scaled Quantum Mechanical force field usually agrees to within 15 cm-1 of the corresponding experimental fundamental vibration frequencies. Rotational constants derived from the r(e) geometry, Scaled Quantum Mechanical fundamental vibration frequencies, and molecular weight are used as inputs for calculating thermodynamic functions via standard statistical mechanic methods, invoking the Born-Oppenheimer and rigid rotor harmonic oscillator approximations. The heat of formation at O K, EO, is calculated either via a method based on atomic equivalents of a method based on isodesmic reactions.


Descriptors :   *FREQUENCY , VIBRATION , EXPERIMENTAL DATA , COMPUTATIONS , THERMODYNAMICS , QUANTUM THEORY , MOLECULAR WEIGHT , FINITE DIFFERENCE THEORY , ELECTRONS , CORRELATION , CONSTANTS , GEOMETRY , ROTATION , ENTHALPY , FREE ENERGY , SPECIFIC HEAT , FORCE(MECHANICS) , ENTROPY , TRUNCATION , FUNCTIONS


Subject Categories : Numerical Mathematics
      Thermodynamics


Distribution Statement : APPROVED FOR PUBLIC RELEASE