Editing First principle (section)

== In physics ==
{{Expand section|date=July 2023}}
In [[physics]], a calculation is said to be ''from first principles'', or ''[[ab initio]]'', if it starts directly at the level of established laws of physics and does not make assumptions such as empirical [[Physical model|model]] and [[Curve fitting|fitting]] parameters.

For example, calculation of [[electronic structure]] using the [[Schrödinger equation]] within a set of approximations that do not include fitting the model to experimental data is an [[ab initio quantum chemistry methods|''ab initio'' approach]].