Spurious proton transfer in hydrogen bonded dimers

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Proton translocation along hydrogen bonds (hb) can occur during geometry optimization using electronic structure methods.
• These proton transfer (pt) events may be artifacts, known as spurious pt events, depending on the computational method used.

Purpose of the Study:

• Investigate spurious pt events in hydrogen bonded dimers of HXN molecules (X = C, Si, Ge, Sn).
• Evaluate the performance of standard exchange-correlation (xc) functional approximations in predicting pt events and hb strength.
• Determine methods to avoid spurious pt events and accurately describe hb interactions.

Main Methods:

• Density Functional Theory (DFT) calculations for geometry optimization.
• Comparison of DFT results with wave function methods.
• Systematic variation of exact exchange (ex) percentage in hybrid xc-functionals.
• Analysis of isolated HXN molecules' geometry and electronic structure.

Main Results:

• Standard xc-functionals inaccurately predict spurious pt events or overly strong hbs for most (HXN)2 dimers.
• Fine-tuning exact exchange percentage can prevent spurious pt events but often inadequately describes the hb.
• Spurious pt events arise from the incorrect description of isolated HXN molecules by xc-functionals lacking sufficient exact exchange.

Conclusions:

• The study highlights the limitations of standard xc-functionals in accurately modeling proton transfer in hydrogen bonded systems.
• A method is proposed to identify spurious pt events by examining the electronic structure and geometry of isolated molecules.
• Accurate computational modeling requires careful selection of xc-functionals and validation against higher-level methods.