Quantum alchemy beyond singlets: Bonding in diatomic molecules with hydrogen.

Area of Science:

• Computational chemistry
• Quantum mechanics
• Chemical bonding theory

Background:

• Bonding energies are crucial for molecular stability.
• Accurate prediction of bonding behavior is essential for exploring chemical space, especially for radicals.
• Quantum alchemy offers a potential method for studying molecular stability.

Purpose of the Study:

• To evaluate quantum alchemy's ability to predict bonding behavior in hypothetical diatomic molecules.
• To compare manual quantum alchemy with Taylor series approximations for predicting molecular properties.
• To identify the most accurate Taylor series truncation order for quantum alchemy predictions.

Main Methods:

• Investigated diatomic molecules involving hydrogen with diverse electronic structures.
• Calculated equilibrium bond lengths, ionization energies, and electron affinities.
• Compared manual quantum alchemy (altering nuclear charge) with Taylor series approximations.

Main Results:

• Manual quantum alchemy calculations provided more accurate predictions than Taylor series approximations.
• Second-order Taylor series truncations yielded the most accurate approximate predictions.
• Prediction trends varied depending on the specific molecular property (bond length, ionization energy, electron affinity).

Conclusions:

• Quantum alchemy, particularly manual calculations, shows promise for predicting molecular bonding.
• Taylor series approximations can be useful, with second-order truncation being optimal.
• Further research is needed to address challenges in predicting bonding for non-singlet systems using quantum alchemy.