Reducing the Computational Cost of Ab Initio Methods

Reducing the Computational Cost of Ab Initio Methods

Date: August 2008
Creator: Mintz, Benjamin
Description: In recent years, advances in computer technology combined with new ab initio computational methods have allowed for dramatic improvement in the prediction of energetic properties. Unfortunately, even with these advances, the extensive computational cost, in terms of computer time, memory, and disk space of the sophisticated methods required to achieve chemical accuracy - defined as 1 kcal/mol from reliable experimental data effectively - limits the size of molecules [i.e. less than 10-15 non-hydrogen atoms] that can be studied. Several schemes were explored to help reduce the computational cost while still maintaining chemical accuracy. Specifically, a study was performed to assess the accuracy of ccCA to compute atomization energies, ionization potentials, electron affinities, proton affinities, and enthalpies of formation for third-row (Ga-Kr) containing molecules. Next, truncation of the correlation consistent basis sets for the hydrogen atom was examined as a possible means to reduce the computational cost of ab initio methods. It was determined that energetic properties could be extrapolated to the complete basis set (CBS) limit utilizing a series of truncated hydrogen basis sets that was within 1 kcal/mol of the extrapolation of the full correlation consistent basis sets. Basis set truncation for the hydrogen atom was then applied to ...
Contributing Partner: UNT Libraries
Application of the Correlation Consistent Composite Approach (ccCA) to Third-Row (Ga-Kr) Molecules

Application of the Correlation Consistent Composite Approach (ccCA) to Third-Row (Ga-Kr) Molecules

Date: January 19, 2008
Creator: DeYonker, Nathan J.; Mintz, Benjamin; Cundari, Thomas R., 1964- & Wilson, Angela K.
Description: This article discusses the application of the correlation consistent composite approach (ccCA) to third-row (Ga-Kr) molecules. The authors applied the ccCA to the G3/05 training set of 51 energetic properties for the atoms and molecules that contain the 4p elements, Ga-Kr.
Contributing Partner: UNT College of Arts and Sciences
Accurate Enthalpies of Formation of Alkali and Alkaline Earth Metal Oxides and Hydroxides: Assessment of the Correlation Consistent Composite Approach (ccCA)

Accurate Enthalpies of Formation of Alkali and Alkaline Earth Metal Oxides and Hydroxides: Assessment of the Correlation Consistent Composite Approach (ccCA)

Date: July 12, 2006
Creator: Ho, Dustin S.; DeYonker, Nathan J.; Cundari, Thomas R., 1964- & Wilson, Angela K.
Description: This article discusses research on accurate enthalpies of formation of alkali and alkaline earth metal oxides and hydroxides. For this research, the authors use a new model chemistry called the correlation consistent Composite Approach (ccCA).
Contributing Partner: UNT College of Arts and Sciences
The correlation-consistent composite approach: Implementation of the resolution-of-the-identity approximation

The correlation-consistent composite approach: Implementation of the resolution-of-the-identity approximation

Date: April 2, 2009
Creator: Lai, Jeremy; Wilson, Angela K. & Prascher, Brian
Description: This presentation discusses research on the correlation-consistent composite approach (ccCA). This research experiment tested RI-ccCA with G2/97 test set, over 100 second-row and third-row molecules, used Molpro, a computational chemistry software package, and the University of North Texas (UNT) Department of Chemistry's CRUNTCh supercomputers.
Contributing Partner: UNT Honors College
The correlation consistent composite approach (ccCA): An alternative to the Gaussian-n methods

The correlation consistent composite approach (ccCA): An alternative to the Gaussian-n methods

Date: March 17, 2006
Creator: DeYonker, Nathan J.; Cundari, Thomas R., 1964- & Wilson, Angela K.
Description: This article discusses the correlation consistent composite approach (ccCA) as an alternative for computing molecular energies.
Contributing Partner: UNT College of Arts and Sciences
Quantum Perspectives on Physical and Inorganic Chemistry

Quantum Perspectives on Physical and Inorganic Chemistry

Date: December 2007
Creator: Grimes-Marchan, Thomas V.
Description: Applications of computational quantum chemistry are presented, including an analysis of the photophysics of cyclic trinuclear coinage metal pyrazolates, an investigation into a potential catalytic cycle utilizing transition metal scorpionates to activate arene C-H bonds, and a presentation of the benchmarking of a new composite model chemistry (the correlation consistent composite approach, ccCA) for the prediction of classical barrier heights. Modeling the pyrazolate photophysics indicates a significant geometric distortion upon excitation and the impact of both metal identity and substituents on the pyrazolates, pointing to ways in which these systems may be used to produce rationally-tuned phosphors. Similarly, thermodynamic and structural investigations into the catalyst system points to promising candidates for clean catalytic activation of arenes. The ccCA was found to reproduce classical reaction barriers with chemical accuracy, outperforming all DFT, ab initio, and composite methods benchmarked.
Contributing Partner: UNT Libraries
Quantitative Computational Thermochemistry of Transition Metal Species

Quantitative Computational Thermochemistry of Transition Metal Species

Date: May 15, 2007
Creator: DeYonker, Nathan J.; Peterson, Kirk A.; Steyl, Gideon; Wilson, Angela K. & Cundari, Thomas R., 1964-
Description: This article discusses quantitative computational thermochemistry of transition metal species. The correlation consistent Composite Approach (ccCA), which has been shown to achieve chemical accuracy (±1 kcal mol⁻¹) for a large benchmark set of main group and s-block metal compounds, is used to compute enthalpies of formation for a set of 17 3d transition metal species.
Contributing Partner: UNT College of Arts and Sciences
The correlation-consistent composite approach: Application to the G3/99 test set

The correlation-consistent composite approach: Application to the G3/99 test set

Date: September 13, 2006
Creator: DeYonker, Nathan J.; Grimes, Thomas V.; Yockel, Scott; Dinescu, Adriana; Mintz, Benjamin; Cundari, Thomas R., 1964- et al.
Description: This article discusses the correlation-consistent composite approach.
Contributing Partner: UNT College of Arts and Sciences
The Multi-reference Correlation Consistent Composite Approach: A New Vista In Quantitative Prediction Of Thermochemical And Spectroscopic Properties

The Multi-reference Correlation Consistent Composite Approach: A New Vista In Quantitative Prediction Of Thermochemical And Spectroscopic Properties

Date: December 2011
Creator: Oyedepo, Gbenga A.
Description: The multi-reference correlation consistent composite approach (MR-ccCA) was designed to reproduce the accuracy of more computationally intensive ab initio quantum mechanical methods like MR-ACPF-DK/aug-cc-pCV?Z-DK, albeit at a significantly reduced cost. In this dissertation, the development and applications of the MR-ccCA method and a variant of its single reference equivalent (the relativistic pseudopotential ccCA method) are reported. MR-ccCA is shown to predict the energetic properties of reactive intermediates, excited states species and transition states to within chemical accuracy (i.e. ±1.0 kcal mol 1) of reliable experimental values. The accuracy and versatility of MR-ccCA are also demonstrated in the prediction of the thermochemical and spectroscopic properties (such as atomization energies, enthalpies of formation and adiabatic transition energies of spin-forbidden excited states) of a series of silicon-containing compounds. The thermodynamic and kinetic feasibilities of the oxidative addition of an archetypal arylglycerol ?-aryl ether (?-O-4 linkage) substructure of lignin to Ni, Cu, Pd and Pt transition metal atoms using the efficient relativistic pseudopotential correlation consistent composite approach within an ONIOM framework (rp-ccCA-ONIOM), a multi-level multi-layer QM/QM method formulated to enhance the quantitative predictions of the chemical properties of heavy element-containing systems larger than hitherto attainable, are also reported.
Contributing Partner: UNT Libraries
Performance of the correlation consistent composite approach for transition states: A comparison to G3B theory

Performance of the correlation consistent composite approach for transition states: A comparison to G3B theory

Date: October 19, 2007
Creator: Grimes, Thomas V.; Wilson, Angela K.; DeYonker, Nathan J. & Cundari, Thomas R., 1964-
Description: This article discusses performance of the correlation consistent composite approach for transition states.
Contributing Partner: UNT College of Arts and Sciences