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In quantum chemistry, size consistency and size extensivity are concepts relating to how the behaviour of quantum-chemistry calculations changes with the system size. Size consistency (or strict separability) is a property that guarantees the consistency of the energy behaviour when interaction between the involved molecular subsystems is nullified (for example, by distance).
The size-consistency and size-extensivity problems of truncated CI are alleviated but still exist. In small molecules, accuracy of the corrected energies can be similar to results from coupled cluster theory calculations. The Davidson correction does not give information about the wave function.
The choice of the exponential ansatz is opportune because (unlike other ansatzes, for example, configuration interaction) it guarantees the size extensivity of the solution. Size consistency in CC theory, also unlike other theories, does not depend on the size consistency of the reference wave function.
The density of water is approximately 1g/mL whether you consider a drop of water or a swimming pool, but the mass is different in the two cases. Dividing one extensive property by another extensive property gives an intensive property—for example: mass (extensive) divided by volume (extensive) gives density (intensive).
Size consistency and size extensivity; Slater determinant; Slater integrals; Slater–Condon rules; Slater-type orbital; Slater's rules; Sonochemistry; Spherium; Spin contamination; Spin engineering; Spin transition; Spin-forbidden reactions; State-universal coupled cluster; STO-nG basis sets; Superatom; Symmetry-adapted perturbation theory
Water is the chemical substance with chemical formula H 2 O; one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. [26] Water is a tasteless, odorless liquid at ambient temperature and pressure. Liquid water has weak absorption bands at wavelengths of around 750 nm which cause it to appear to have a blue color. [4]
where μ is the electric dipole moment of the effectively polarized water molecule (2.35 D for the SPC/E model), μ 0 is the dipole moment of an isolated water molecule (1.85 D from experiment), and α i is an isotropic polarizability constant, with a value of 1.608 × 10 −40 F·m 2. Since the charges in the model are constant, this ...
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