Convert Hartree or Rydberg energy to electronvolts (eV), or reverse the conversion. Choose Solve for, enter an energy, and select Calculate.

Convert Hartree or Rydberg energy to electronvolts. Signed energies and zero are supported.

Eₕ = Hartree; Ry = Rydberg. Switching units converts the number.

Atomic Units to eV Formula

The following formulas are used to convert atomic units of energy into electronvolts (eV).

E(eV) ≈ E(a.u.) × 27.211386245981
E(eV) ≈ E(Ry) × 13.6056931229905

Variables:

  • E(eV) is the energy in electronvolts
  • E(a.u.) is the energy in atomic units, typically Hartree
  • E(Ry) is the energy in Rydberg units
  • 27.211386245981 is the 2022 CODATA recommended Hartree-to-eV factor
  • 13.6056931229905 is the Rydberg-to-eV factor used here (half the Hartree value)

To calculate the energy in eV, multiply the energy value in atomic units by the appropriate conversion factor.

What are Atomic Units and eV?

Atomic units are a natural unit system used in quantum chemistry and atomic physics. In this system, several fundamental constants are normalized to 1, making equations easier to work with. The Hartree is the standard atomic unit of energy, while the Rydberg is another commonly used energy unit closely related to the Hartree. Electronvolts (eV) are more widely used in chemistry, spectroscopy, and solid-state physics because they provide a convenient scale for describing atomic and molecular energies.

How to Convert Atomic Units to eV?

The following steps outline how to convert atomic units of energy to electronvolts.

  1. First, determine the numerical energy value in atomic units.
  2. Next, identify whether the value is given in Hartree or Rydberg.
  3. Use the correct formula: multiply Hartree values by 27.211386245981 or Rydberg values by 13.6056931229905. Divide by the same factor for the reverse conversion.
  4. After calculating the result, compare your answer with the converter above.

Atomic Units to eV Conversion Table

The table below uses the 2022 CODATA Hartree energy value; factors and results shown in the table are rounded to four decimals.

Energy in Atomic Units Conversion Factor Value in eV
0.1 Eₕ 27.2114 eV per Eₕ 2.7211 eV
0.5 Eₕ 27.2114 eV per Eₕ 13.6057 eV
1 Eₕ 27.2114 eV per Eₕ 27.2114 eV
2 Eₕ 27.2114 eV per Eₕ 54.4228 eV
5 Eₕ 27.2114 eV per Eₕ 136.0569 eV
10 Eₕ 27.2114 eV per Eₕ 272.1139 eV
1 Ry 13.6057 eV per Ry 13.6057 eV

Many quantum chemistry programs report total electronic energies in Hartree, while many reference values in experimental chemistry and physics are listed in eV. Because the conversion factors are fixed constants, it is straightforward to move between these unit systems for comparison and analysis.

Example Problem:

Use the following values as an example problem to test your knowledge.

Energy = 2 Hartree

Conversion Factor ≈ 27.211386245981 eV per Hartree

Result ≈ 54.42277249 eV