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In chemistry, the lever rule is a formula used to determine the mole fraction (x i) or the mass fraction (w i) of each phase of a binary equilibrium phase diagram.It can be used to determine the fraction of liquid and solid phases for a given binary composition and temperature that is between the liquidus and solidus line.
Spartan is a molecular modelling and computational chemistry application from Wavefunction. [2] It contains code for molecular mechanics, semi-empirical methods, ab initio models, [3] density functional models, [4] post-Hartree–Fock models, [5] and thermochemical recipes including G3(MP2) [6] and T1. [7]
On the other hand, the simplest ab initio calculations formally scale as O(N 3) or worse (restricted Hartree–Fock calculations have been suggested to scale ~O(N 2.7)). Here in the ab initio calculations, N stands for the number of basis functions rather than the number of atoms. Each atom has at least as many basis functions as is the number ...
A force field is used to minimize the bond stretching energy of this ethane molecule.. Molecular mechanics uses classical mechanics to model molecular systems. The Born–Oppenheimer approximation is assumed valid and the potential energy of all systems is calculated as a function of the nuclear coordinates using force fields.
Theoretical chemistry requires quantities from core physics, such as time, volume, temperature, and pressure.But the highly quantitative nature of physical chemistry, in a more specialized way than core physics, uses molar amounts of substance rather than simply counting numbers; this leads to the specialized definitions in this article.
Quantum chemistry composite methods (also referred to as thermochemical recipes) [1] [2] are computational chemistry methods that aim for high accuracy by combining the results of several calculations. They combine methods with a high level of theory and a small basis set with methods that employ lower levels of theory with larger basis sets ...
PM3, or Parametric Method 3, is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Differential Diatomic Overlap integral approximation. The PM3 method uses the same formalism and equations as the AM1 method. The only differences are: 1) PM3 uses two ...
Ab initio quantum chemistry methods are computational chemistry methods based on quantum chemistry. [1] The term ab initio was first used in quantum chemistry by Robert Parr and coworkers, including David Craig in a semiempirical study on the excited states of benzene. [2] [3] The background is described by Parr. [4]