Ab initio multiple spawning
Encyclopedia
The ab initio multiple spawning, or AIMS, method is a time-dependent formulation
of quantum chemistry
.
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
from first principles molecular dynamics, with no empirical parameters. The method has been applied to two molecules of interest in organic photochemistry—ethylene
and cyclobutene
.
The photodynamics of ethylene
involves both covalent and ion
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
is established within the first 50 fs after optical excitation.
The method was developed by chemistry professor Todd Martinez
.
Formulation
Formulation may refer to:* Clinical formulation* Formulations * Formulation science* Pharmaceutical formulation:** Galenic formulation* Pesticide formulation...
of quantum chemistry
Quantum chemistry
Quantum chemistry is a branch of chemistry whose primary focus is the application of quantum mechanics in physical models and experiments of chemical systems...
.
In AIMS, nuclear dynamics and electronic structure problems are solved simultaneously. Quantum mechanical effects
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
in the nuclear dynamics are included, especially the nonadiabatic effects
Vibronic coupling
In theoretical chemistry, the vibronic coupling terms, , are proportional to the interaction between electronic and nuclear motions of molecules. The term "vibronic" originates from the concatenation of the terms "vibrational" and "electronic"...
which are crucial in modeling dynamics on multiple electronic states.
The AIMS method makes it possible to describe photochemistry
Photochemistry
Photochemistry, a sub-discipline of chemistry, is the study of chemical reactions that proceed with the absorption of light by atoms or molecules.. Everyday examples include photosynthesis, the degradation of plastics and the formation of vitamin D with sunlight.-Principles:Light is a type of...
from first principles molecular dynamics, with no empirical parameters. The method has been applied to two molecules of interest in organic photochemistry—ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...
and cyclobutene
Cyclobutene
Cyclobutene is a cycloalkene. It is used in the chemical industry as a monomer for synthesis of some polymers and for a range of chemical syntheses.- External links :*...
.
The photodynamics of ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...
involves both covalent and ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
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
Woodward-Hoffmann rules
The Woodward–Hoffmann rules devised by Robert Burns Woodward and Roald Hoffmann are a set of rules in organic chemistry predicting the stereochemistry of pericyclic reactions based on orbital symmetry. These include electrocyclic reactions, cycloadditions , sigmatropic reactions, and group transfer...
is established within the first 50 fs after optical excitation.
The method was developed by chemistry professor Todd Martinez
Todd Martinez
Todd J. Martínez is a David Mulvane Ehrsam and Edward Curtis Franklin Professor of Chemistry at Stanford University and a Professor of Photon Science at the SLAC National Accelerator Laboratory. He received his B.S . from Calvin College in 1989 and his Ph.D. from UCLA in 1994...
.