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The Mystery of Quantum Chemistry: How does the Hartree-Fock method reveal the connection between atoms?
In the field of quantum chemistry, understanding how electrons move through interactions between atoms is key to understanding chemical reactions.The Hartree–Fock method is an effective technique for calculating molecular orbitals, which is based on the linear combination of atomic orbitals, revealing complex connections between atoms.
Describe the electron configuration of an atom using an electron wave function so that each atom can be regarded as a cloud-like structure composed of a wave function.
As early as 1929, Sir John Leonard-Jones first introduced this concept, further clarifying the bonding of two atomic molecules in the main family elements, but before that, Linus Pauling had already made hydrogen molecules ions Similar studies were conducted for H2+.
In the Hartree–Fock method, it is assumed that the number of molecular orbitals equals the number of atomic orbitals involved in linear expansion.This view means that n atomic orbitals can be combined into n molecular orbitals, and these molecular orbitals will exhibit their respective characteristics.
The mathematical descriptions of these molecular orbitals are usually: 𝜙i = c1i𝜒1 + c2i 𝜒2 + ... + cni𝜒n, where c represents the coefficient corresponding to each atomic orbital.
And to find these coefficients, the Hartrie-Fokker method is used to minimize the total energy of the system.This quantitative method helps scientists accurately calculate the interaction between atoms in chemical reactions.
However, with the development of computational chemistry, the LCAO method is not limited to the actual optimization of wave functions, but is also used as a tool for qualitative discussions to help predict and interpret the results obtained by more modern methods.
By comparing the atomic orbital energy of individual atoms and applying known interaction rules, the shape of molecular orbitals and their respective energies can be roughly inferred.
The use of charts can further clearly express these arguments, which are called correlation graphs.The resulting atomic orbital energy can be obtained by calculating or relying on experimental data from Kupman's theorem.
The first step in this process is to assign a point group to the molecules.Each group operation is applied to the molecule, and the number of unpassive bonds is the character of the operation.This form of reducible representation is decomposed into the sum of irreducible representations, which represent symmetry corresponding to the involved orbits.
The molecular orbital map provides a simple qualitative description of LCAO processing, while the Hekel method, the extended Hekel method, and the Pariser–Parr–Pople method provide some quantitative theoretical support.
How exactly does the Hartree–Fock approach affect our understanding of chemical reactions?These studies not only help us reveal the connections between atoms, but also prompt us to think about the next path?
