Ab Initio
Definition and meaning of Ab Initio in chemistry.
Ab initio, Latin for “from the beginning,” describes computational chemistry methods that calculate the properties of molecules directly from the fundamental laws of quantum mechanics, without relying on experimental data as input.
In more detail
Ab initio methods solve approximations to the Schrödinger equation, starting only from the positions and charges of the atomic nuclei and electrons. The best-known example is the Hartree–Fock method, with more accurate approaches building on it. These calculations can be very accurate but are computationally expensive, so they contrast with faster semi-empirical methods that use experimentally derived parameters.
Key facts
| Meaning | “From the beginning” (Latin) |
|---|---|
| Based on | Quantum mechanics |
| Example method | Hartree–Fock |
| Field | Computational chemistry |
A chemist might use an ab initio calculation to predict the shape and energy of a small molecule that has never been made in the laboratory.
Frequently asked questions
What does ab initio mean in chemistry?
It refers to calculating molecular properties purely from quantum-mechanical first principles, without using experimental measurements as input.
How is ab initio different from semi-empirical methods?
Ab initio methods use no experimental parameters and are more accurate but slower, while semi-empirical methods include fitted parameters to run faster with less accuracy.