Efficient implementation of analytical Raman intensities.

Area of Science:

• Computational Chemistry
• Spectroscopy
• Quantum Chemistry

Background:

• Accurate prediction of Raman spectra is crucial for molecular characterization.
• Previous methods for calculating polarizability gradients were computationally expensive.
• The ORCA program is a widely used quantum chemistry package.

Purpose of the Study:

• To implement an analytical derivative of static polarizability gradients in the ORCA program.
• To improve the efficiency and scalability of Raman spectra calculations.
• To enable the analysis of larger and more complex molecular systems.

Main Methods:

• Developed an analytical derivative implementation for static polarizability gradients.
• Utilized RIJ and COSX integral approximations for improved computational scaling.
• Incorporated CPCM for solvent effect calculations.
• Introduced an automatic procedure to augment auxiliary basis sets for RIJ error reduction.

Main Results:

• Achieved speedups of 1-2 orders of magnitude compared to numerical derivatives.
• Demonstrated the safety of RIJ and COSX approximations for routine calculations.
• Enabled fully analytical harmonic Raman spectra calculations for systems exceeding 100 atoms.
• Showed that polarizability gradient calculations add less than 10% overhead to Hessian calculations.

Conclusions:

• The new analytical implementation significantly enhances the efficiency of Raman spectra prediction.
• The method is robust and accurate, suitable for routine calculations.
• This development facilitates the study of larger molecules and complex chemical systems through Raman spectroscopy.