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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 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 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.
Quadratic configuration interaction [1] (QCI) is an extension of configuration interaction [2] that corrects for size-consistency errors in single and double excitation CI methods (CISD). [ 3 ] Size-consistency means that the energy of two non-interacting (i.e. at large distance apart) molecules calculated directly will be the sum of the ...
He also promoted the concept of size extensivity for many-body theory that scales properly with the number of particles, now viewed as an essential element of sound quantum chemistry approximations. Bartlett was also the first to explore the combination of coupled-cluster and many-body perturbation theories (in 1985) and proposed vastly ...
TSS of a water or wastewater sample is determined by pouring a carefully measured volume of water (typically one litre; but less if the particulate density is high, or as much as two or three litres for very clean water) through a pre-weighed filter of a specified pore size, then weighing the filter again after the drying process that removes all water on the filter.
Fluoride has been added to public water supplies in the U.S. for decades. No studies in the U.S. have flagged any measurable decreases in children's cognitive development since fluoride was ...
The consistency index (Ic) indicates a soil's consistency (firmness). It is calculated as CI = (LL-W)/(LL-PL), where W is the existing water content. The soil at the liquid limit will have a consistency index of 0, the soil at the plastic limit will have a consistency index of 1, and if W > LL, Ic is negative.