Assessing spin-component-scaled second-order Møller-plesset theory using anharmonic frequencies.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Spectroscopy

Background:

• Accurate prediction of molecular vibrational frequencies is crucial for understanding molecular properties and reactions.
• Second-order Møller-Plesset (MP2) perturbation theory is a widely used method for electronic structure calculations.
• Spin-component scaling in MP2 theory aims to improve accuracy by optimizing the treatment of different spin components.

Purpose of the Study:

• To benchmark four common spin-component-scaled MP2 (SCS-MP2) parametrizations against standard MP2 theory.
• To evaluate the performance of these methods in calculating anharmonic vibrational frequencies for diatomic and small molecules.
• To identify the most accurate and computationally efficient SCS-MP2 method for vibrational frequency predictions.

Main Methods:

• Calculation of anharmonic vibrational frequencies using four SCS-MP2 variants: SOS-MP2, VOS-MP2, SCS-MP2, and SCSN-MP2.
• Benchmarking against experimental data for a test set of eighteen diatomic and five small molecules.
• Statistical analysis of mean absolute deviations (ε(MAD)) to assess accuracy.

Main Results:

• SOS-MP2, VOS-MP2, and SCS-MP2 methods showed statistically better performance than standard MP2 theory.
• SOS-MP2 provided slightly better accuracy for closed-shell diatomic molecules (ε(MAD) = 51 cm⁻¹).
• VOS-MP2 demonstrated the best accuracy for open-shell diatomic molecules (ε(MAD) = 77 cm⁻¹).

Conclusions:

• VOS-MP2 and SOS-MP2 methods exhibit smaller deviations from experimental vibrational frequencies.
• These methods offer potential for greater computational economy compared to SCS-MP2 and standard MP2.
• VOS-MP2 and SOS-MP2 are recommended as preferred ab initio methods for computing vibrational frequencies in large molecules.