The ab initio multiple spawning, or AIMS, method is a time-dependent

formulation Formulation is a term used in various senses in various applications, both the material and the abstract or formal. Its fundamental meaning is the putting together of components in appropriate relationships or structures, according to a formula ...

quantum chemistry Quantum chemistry, also called molecular quantum mechanics, is a branch of physical chemistry focused on the application of quantum mechanics to chemical systems, particularly towards the quantum-mechanical calculation of electronic contributions ...

. In AIMS, nuclear dynamics and electronic structure problems are solved simultaneously. Quantum mechanical effects in the nuclear dynamics are included, especially the nonadiabatic effects which are crucial in modeling dynamics on multiple electronic states. The AIMS method makes it possible to describe

photochemistry Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 Nanometre, nm), visible ligh ...

from first principles molecular dynamics, with no empirical parameters. The method has been applied to two molecules of interest in organic photochemistry -

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...

and

cyclobutene Cyclobutene is an organic compound with the chemical formula . It is a cycloalkene. It is a colorless gas that easily condenses. It is of interest in research but currently has no practical applications. A modern synthesis involves the 2-step deh ...

. The photodynamics of

involves both

covalent A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atom ...

and

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

ic electronic excited states and the return to the ground state proceeds through a pyramidalized geometry. For the photoinduced ring opening of cyclobutene, is it shown that the disrotatory motion predicted by the

Woodward–Hoffmann rules The Woodward–Hoffmann rules (or the pericyclic selection rules) are a set of rules devised by Robert Burns Woodward and Roald Hoffmann to rationalize or predict certain aspects of the stereochemistry and activation energy of Pericyclic reaction, ...

is established within the first 50 fs after optical excitation. The method was developed by chemistry professor Todd Martinez.

References

* Ab Initio Multiple Spawning: Photochemistry from First Principles Quantum Molecular Dynamics, M. Ben-Nun, Jason Quenneville, and Todd J. Martínez, ''J. Phys. Chem. A'' 104 (2000), #22, pp. 5161–5175. DO
10.1021/jp994174i
* Nonadiabatic molecular dynamics: Validation of the multiple spawning method for a multidimensional problem, M. Ben-Nun and Todd J. Martínez, ''Journal of Chemical Physics'' 108, #17 (May 1, 1998), pp. 7244–7257. DO
10.1063/1.476142
Quantum chemistry Theoretical chemistry {{quantum-chemistry-stub