Definition: Compose a new way to ask the same question. The new question must be asking the exact same thing as the original question does. Without any other information, you should be able to tell that the original question and the new question are the same. Preserve bracketed phrases in your new question. You can change the rest of the question provided the above requirements are satisfied. The new question must have a natural, fluent formulation, as if it were composed by a native English speaker. You will be given three pieces of information to help you create better questions. Those are: "Answer": the answer to the question, e.g., "Honolulu". "Answer Type": the type of the answer, e.g., "Location". "Auxiliary Information" is a detailed description of some concepts mentioned in the question, if any.
Input: original question: Which measurement system has the energy units [Hartree]?
answer: atomic units
answer type: Measurement System.
auxiliary information: The hartree, also known as the Hartree energy, is the atomic unit of energy, named after the British physicist Douglas Hartree. It is defined as 2R‚àûhc, where R‚àû is the Rydberg constant, h is the Planck constant and c is the speed of light. The 2010 CODATA recommended value is E‚Çï = 4.359 744 34√ó10^‚àí18 J = 27.211 385 05 eV. The 2006 CODATA recommended value was E‚Çï = 4.359 743 94 √ó10^‚àí18 J = 27.211 383 86 eV. The hartree energy is approximately the electric potential energy of the hydrogen atom in its ground state and, by the virial theorem, approximately twice its ionization energy; the relationships are not exact because of the finite mass of the nucleus of the hydrogen atom and relativistic corrections. The hartree is usually used as a unit of energy in atomic physics and computational chemistry: for experimental measurements at the atomic scale, the electronvolt or the reciprocal centimetre are much more widely used.

[Hartree] has the energy units of which measurement system?