The combined fragmentation and systematic molecular fragmentation methods.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Organic Chemistry

Background:

• Molecular reactivity is traditionally linked to functional groups, but sophisticated quantum calculations often obscure this relationship.
• Accurate estimation of molecular electronic energy is crucial for understanding chemical reactivity.
• Calculating energies for large molecules using traditional ab initio methods is computationally intensive and time-consuming.

Purpose of the Study:

• To introduce and explain two fragmentation methods: combined fragmentation method (CFM) and systematic molecular fragmentation (SMF).
• To demonstrate the application of these methods for estimating energies and properties of molecules and nonconducting crystals.
• To highlight the practical advantages of fragmentation methods in computational chemistry.

Main Methods:

• Decomposing molecules into small fragments of adjacent functional groups.
• Estimating electronic energy as a sum of fragment energies.
• Applying systematic molecular fragmentation (SMF) to periodic crystal structures for energy and property calculations.

Main Results:

• Fragmentation methods (CFM and SMF) enable accurate estimation of molecular electronic energy to chemical accuracy.
• These methods significantly reduce computational time and cost, making calculations for large molecules feasible.
• The approaches accurately estimate derivatives of molecular and crystal energies, enabling property predictions like NMR and vibrational spectra.

Conclusions:

• Fragmentation methods represent a significant practical advancement in computational chemistry.
• CFM and SMF allow for accurate and efficient energy calculations of large organic and biological molecules.
• These methods facilitate the study of molecular reactivity and properties, previously limited by computational constraints.