The geometry of a set of atoms can be described by a vector, r, where the elements in the vector come from the atoms' positions. Vector r could be the set of the Cartesian coordinates of the atoms and could also be a set of inter-atomic distances and angles.
Given r, one can introduce the concept of the energy as a function of the positions, E(r). It is the value of E(r) for all r of interest that, using the landscape analogy from the introduction, gives height of the "land" on the "energy landscape" and it is from here that the concept of a potential energy surface arises.
To study a chemical reaction using the PES of the constituent atoms, it must be possible to calculate the energy for every arrangement of the atoms that one is interested in. Methods of calculating the energy of a particular arrangement of atoms is well described in the Computational Chemistry article, and the emphasis here will be on forming approximations of E(r) for when fine-grained energy-position information is desired.
For very simple chemical systems or when significant assumptions are made about inter-atomic interactions, it is sometimes possible to use an analytically derived expression for the energy as a function of the atomic positions, for example the London-Eyring-Polanyi-Sato[citation needed] potential for the system H + H2.
Often, for more complicated systems, calculation of the energy of a particular arrangement of atoms is too computationally expensive for large scale representations of the surface to be feasible. For these systems a possible approach is to calculate only a reduced set of points on the PES and then use a computationally cheaper interpolation method, for example Shepard interpolation, to fill in the gaps.[2]
The geometry of a set of atoms can be described by a vector, r, where the elements in the vector come from the atoms' positions. Vector r could be the set of the Cartesian coordinates of the atoms and could also be a set of inter-atomic distances and angles.
Given r, one can introduce the concept of the energy as a function of the positions, E(r). It is the value of E(r) for all r of interest that, using the landscape analogy from the introduction, gives height of the "land" on the "energy landscape" and it is from here that the concept of a potential energy surface arises.
To study a chemical reaction using the PES of the constituent atoms, it must be possible to calculate the energy for every arrangement of the atoms that one is interested in. Methods of calculating the energy of a particular arrangement of atoms is well described in the Computational Chemistry article, and the emphasis here will be on forming approximations of E(r) for when fine-grained energy-position information is desired.
For very simple chemical systems or when significant assumptions are made about inter-atomic interactions, it is sometimes possible to use an analytically derived expression for the energy as a function of the atomic positions, for example the London-Eyring-Polanyi-Sato[citation needed] potential for the system H + H2.
Often, for more complicated systems, calculation of the energy of a particular arrangement of atoms is too computationally expensive for large scale representations of the surface to be feasible. For these systems a possible approach is to calculate only a reduced set of points on the PES and then use a computationally cheaper interpolation method, for example Shepard interpolation, to fill in the gaps.[2]
การแปล กรุณารอสักครู่..