Electron iso-density surfaces provide a thermodynamically consistent representation of atomic and molecular surfaces

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Materials Science

Background:

• The surface area of atoms and molecules is critical for material properties.
• Defining molecular surfaces precisely has been a long-standing challenge.
• Bader's definition of molecular surfaces as iso-density contours lacks experimental validation.

Purpose of the Study:

• To experimentally verify theoretical definitions of atomic and molecular surfaces.
• To determine a precise electron density cut-off value for representing molecular surfaces.
• To bridge the gap between quantum chemical calculations and experimental measurements.

Main Methods:

• Utilized a state-of-the-art experimental method based on thermodynamically effective (TE) surfaces.
• Studied a diverse set of 104 molecules.
• Compared experimental results with quantum chemical evaluations of iso-density surfaces.

Main Results:

• Demonstrated excellent agreement between experimental data and quantum chemical calculations.
• Identified an electron density cut-off of 0.0016 atomic units (a.u.) as a reliable surface representation.
• Achieved a mean unsigned percentage deviation of 1.6% and a correlation coefficient of 0.995.

Conclusions:

• The iso-density surface at 0.0016 a.u. electron density accurately represents atomic and molecular surfaces.
• This finding provides experimental validation for theoretical surface definitions.
• The study establishes a new standard for defining molecular surfaces experimentally.