# ReferencingΒΆ

Enthalpies calculated using VASP (and some other computational methods)
have different references than standard references (i.e. the enthalpy of
formation of pure substances, like O_{2} or Pt, is not necessarily
zero). This difference makes it difficult to ensure thermodynamic consistency
for our mechanisms since we may be mixing experimental gas thermodynamics with
computational surface thermodynamics. In order to make the references
consistent, we find a correction factor for each element by solving the
equation:

\(\underline {\underline {H}}^{expt}_{[M \times N]} = \underline {\underline {H}}^{DFT}_{[M \times N]} + \underline {\underline {x}}_ {[M \times N]} \underline{\mathbf{h}}_{[N]}\)

where M is the number of reference species, N is the number of elements,
H^{expt} is the experimental standard enthalpies,
H^{DFT} is the standard enthalpies calculated using DFT,
**x** is a matrix that describes the composition of the references (each row
represents a specie, each column represents an element), and **h** is the
correction for each element.

The equation can be solved using a Least Squares approach.
The correction factor can then be added to subsequent species calculated
through DFT to ensure consistent references. Referencing is handled by the
`References`

.