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ab initio

ab initio: from the beginning
Definition:[lat. “from the beginning”] parameter free methods based on quantum mechanics and electrodynamics using solely universal fundamental physical constants.
Explanation:The term ab initio may be used in different contexts. From a natural science and technical point of view, a calculation is said to be “ab initio” or "from first principles", if it relies on fundamental laws of nature without additional assumptions or special models in contrast to the practices in according measurements. The difference between an ab initio calculation and experimental results may reveal errors in the experimental setup. Moreover, ab initio calculation may accurately determine underlying parameters and display an unknown effect at the moment. The use of measured values is about so called semi-empirical calculations.

In chemistry, the terminology is used in two ways. Firstly, the ab initio synthesis means the production of a chemical compound based on simple chemicals. Secondly, the term may refer to ab initio quantum chemistry methods. In combination with quantum mechanics, it means solving the Schrödinger’s equation without any empirical parameters.

For example, an ab initio calculation of the properties of liquid water might start with the properties of the constituent hydrogen and oxygen atoms and the laws of electrodynamics. From these, the properties of isolated individual water molecule is derived, and the interaction of larger group of water molecules are computed until the bulk properties are determined (Fig. 1).

Furthermore, ab initio has a meaning in other fields. If it comes to biophysics, ab initio may also yield a method for the prediction of protein structures in protein folding. In aviation, it means the flight training from the very first stage of the pedestrian to the pilot. As a legal term it refers to something being the case from the start or from the instant of the act, rather than from when the court declared it so. A judicial declaration of the invalidity of a marriage ab initio is a nullity.
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Diagram:

Fig. 1: Model of water molecules for the ab initio calculation of liquid water properties.
SFB-Link:In the SFB, the calculations are used for the prediction of possible chemical compositions with their according desired mechanical properties. This can include the knowledge of the dominating deformation mechanisms and the following mechanical characteristics.