Assessment of G3(MP2)∕∕B3 theory including a pseudopotential for molecules containing first-, second-, and third-row...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate prediction of thermochemical properties is crucial in chemistry.
• Existing methods like G3(MP2)∕∕B3 theory provide a basis for such calculations.
• The computational cost of all-electron methods can be a limiting factor.

Purpose of the Study:

• To develop and evaluate a modified theoretical method, G3(MP2)∕∕B3-CEP, incorporating compact effective potential (CEP) pseudopotentials.
• To assess the accuracy of G3(MP2)∕∕B3-CEP for calculating thermochemical properties of representative elements.
• To compare the computational efficiency of G3(MP2)∕∕B3-CEP with the all-electron G3(MP2)∕∕B3 theory.

Main Methods:

• Modification of G3(MP2)∕∕B3 theory to include CEP pseudopotentials, creating G3(MP2)∕∕B3-CEP.
• Validation against the G3/05 test set, comprising 446 experimental energies.
• Application to calculate standard enthalpies of formation, ionization energies, electron affinities, proton affinities, and atomization energies.

Main Results:

• G3(MP2)∕∕B3-CEP achieved a mean absolute deviation of 1.6 kcal mol⁻¹ for thermochemical results, comparable to G3(MP2)∕∕B3's 1.4 kcal mol⁻¹.
• Approximately 70% of calculated properties using G3(MP2)∕∕B3-CEP showed accuracy within ±2 kcal mol⁻¹.
• CPU time was reduced by 10%–40% with the G3(MP2)∕∕B3-CEP method.

Conclusions:

• G3(MP2)∕∕B3-CEP offers a computationally efficient alternative to all-electron methods for thermochemical calculations.
• The pseudopotential approach maintains high accuracy, similar to traditional all-electron theories.
• This method provides a valuable tool for studying the energetics of chemical species.