Molecular orbital Calculations which use all the molecular orbitals in a calculation, not just the valence electron orbitals. Absolute configuration The way, in 3-dimensional space, in which 4 different substituents are arranged off a chiral carbon. This can only be determined by X-ray Crystallography. However other compounds which can be related to one with known configuration, by syntheses where there are no changes at a chiral centre, bcan also be assigned an absolute configuration
calculation - a method of calculating chemical properties of molecules directly from the first principles of quantum mechanics, without using empirical parameters ie quantities derived from experiments ( ab initio is Latin for "from the beginning"). Quantum mechanics is a system of mechanics developed from quantum theory which deals with the behavior of fundamental particles and is used to explain the properties of atoms and molecules.
literally "from the beginning." When an agreement is for legal reasons void ab initio, it is void for all purposes throughout the period of its purported existence, and not merely from the moment that it is declared to have been void by the Court. When a man enters upon lands or into the house of another by authority of law, and afterwards abuses that authority, he becomes a trespasser ab initio. Bac. Ab. Trespass, B.; 8 Coke, 146 2 Bl. Rep. 1218 Clayt. 44. And if an officer neglects to remove goods attached within a reasonable time and continue in possession, his entry becomes a trespass ab initio. 2 Bl. Rep. 1218. See also as to other cases, 2 Stra. 717 1 H. Bl. 13 11 East, 395 2 Camp. 115 2 Johns. 191; 10 Johns. 253; ibid. 369. but in case of an authority in fact, to enter, an abuse of such authority will not, in general, subject the party to an action of trespass, Lane, 90 ; Bae. Ab. Trespass, B ; 2 T. It. 166. See generally 1 Chit. PI. 146. 169. 180.
1. A phrase taken from Latin, meaning "from the beginning." 2. There are two strands of approach to the computation of molecular structure. In the semiempirical approach, the calculation draws on a number of experimentally determined characteristics to help in the overall calculation. In the ab initio approach, the calculation proceeds from first principles (the Schrödinger equation) and makes no use of imported information. The former approach was dominant in the 1970s, but increases in computing power have led to an ascendancy of ab initio techniques since then. The latter are intrinsically more reliable because there can be no certainty that a quantity determined in one context is appropriate to a particular molecule.
A way of calculating molecular dynamics for the purpose of a simulation, those calculations being based on the basic chemical properties (such as covalent bonds, hydrogen bonds, van der waals forces, etc.)