ConverterHub

Hartree (Eh) to Electronvolts Converter

Enter a value in hartree (eh) to convert it to electronvolts, joules.

How it is calculated

The converter multiplies by fixed constants: eV = Eh × 27.211386245 and J = Eh × 4.3597447×10−18. The electronvolt result is rounded to four decimals with a thousands separator; the joule result is written in scientific notation with five significant digits (for example 2.1799e-18, meaning 2.1799 × 10−18). Any real number is accepted, including negative values, which are common because total electronic energies from quantum-chemistry programs are negative. The tool only changes units. It does not add zero-point or thermal corrections, and it does not give kJ/mol or kcal/mol, so for those you need a further conversion step on the joule or eV value.

Worked example

Half a hartree is the binding energy of the electron in the hydrogen ground state. Multiplying 0.5 × 27.211386245 gives 13.6057 eV, rounded to four decimals. In joules, 0.5 × 4.3597447×10−18 = 2.1799e-18 J. A reaction barrier of 0.0001 Eh would convert to 0.0027 eV, which shows how small differences in hartrees carry a meaningful energy in electronvolts.

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Common mistakes

  • Dropping the sign. Total energies from ab initio output are negative, and the converted value keeps that sign, so -76.4 Eh is about -2,078.9499 eV.
  • Rounding hartree values too early. A difference of 0.001 Eh is already 0.0272 eV, so keep all digits from the program before converting.
  • Reading the joule result as a plain number. 2.1799e-18 means 2.1799 × 10−18, a tiny amount per atom or molecule, not per mole.
  • Using the result for molar energies. The values are per particle; kJ/mol needs the Avogadro constant as a further step.
  • Confusing the hartree with the rydberg. One hartree is two rydbergs, so mixing them up doubles or halves the answer.

About this calculator

The hartree (Eh) is the atomic unit of energy used in quantum chemistry and computational physics, defined so that it equals twice the ionization energy of a hydrogen atom in its ground state: 1 Hartree = 27.211386 electronvolts = 4.3597447 × 10⁻¹⁸ joules. Working in Hartree atomic units lets quantum-chemistry software drop most physical constants (reduced Planck constant, electron mass, elementary charge) from its equations by setting them to 1, which simplifies both the math and the numerical precision of the calculation.

Computational chemists and physicists running ab initio and density functional theory (DFT) packages (like Gaussian, ORCA, or VASP) constantly convert Hartree output — orbital energies, reaction barriers, bond dissociation energies — into electronvolts or kJ/mol, since those are the units used in experimental spectroscopy and everyday chemistry.

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