# Synopsis: Golden Mystery Solved

A long-standing discrepancy between experiments and theory concerning the electronic properties of gold has now been resolved.

Gold’s lustrous color is due to unusually strong relativistic effects. The same effects also complicate theoretical computations of gold’s electronic properties. Indeed, theorists working on this precious metal have struggled for decades to resolve a discrepancy between their predictions and experimental observations. New work has solved this problem by calculating the electron correlation contribution to an unprecedented level of precision that incorporates “pentuple” interactions between five electrons.

Calculating an atom’s electronic properties is never easy, especially for heavy atoms whose strong Coulomb potential implies relativistic energies for its electrons. In gold’s case, relativistic effects cause a smaller than expected gap between the $6s$ and $5d$ orbitals, which is why gold absorbs blue frequencies and reflects a yellowish tint. But other aspects of gold are more difficult to explain. Calculations of the ionization energy (energy to remove an electron) and electron affinity (energy to add an electron) have consistently underestimated the experimental values by tens of milli-electron-volts.

Peter Schwerdtfeger from Massey University Auckland in New Zealand and his colleagues have performed precise calculations for gold. Their model accounts for relativistic effects, as well as for the contributions from electron correlations and quantum electrodynamics. Electron correlations embody all the electron-electron interactions that occur in a multielectron atom. Previous studies have dealt with electron correlations between the 79 electrons in gold, but typically they have only gone as far as triple interactions between three electrons. Schwerdtfeger’s team extended these calculations to quadruple and pentuple interactions. By doing so, they reduced the discrepancy in the ionization energy and electron affinity to just a few milli-electron-volts —a factor of 10 improvement over past results. The methodology could be applied to even heavier elements.

This research is published in Physical Review Letters.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics based in Lyon, France.

More Features »

### Announcements

More Announcements »

## Subject Areas

Materials Science

Spintronics

Read More »

## Next Synopsis

Nonlinear Dynamics

Read More »

## Related Articles

Condensed Matter Physics

### Viewpoint: Pushing Towards Room-Temperature Superconductivity

Two independent studies report superconductivity at record high temperatures in hydrogen-rich materials under extreme pressure. Read More »

Mechanics

### Focus: Video—Slow-Motion Footage Captures Rubber Band Ripples

Videos of a moving rubber band show that the band takes on previously unpredicted wavy shapes when it is shot through the air. Read More »

Materials Science

### Focus: A Home for Helium inside Earth

Computations predict the existence of a compound that could store the primordial helium that is known to be present somewhere inside the Earth. Read More »