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Contracted basis sets segmented contraction

Most calculations today are done by choosing an existing segmented GTO basis set. These basis sets are identihed by one of a number of notation schemes. These abbreviations are often used as the designator for the basis set in the input to ah initio computational chemistry programs. The following is a look at the notation for identifying some commonly available contracted GTO basis sets. [Pg.81]

All of the above basis sets are of the segmented contraction type. Modem contracted basis sets aimed at producing very accurate wave functions often employ a general contraction scheme. The ANO and cc basis sets below are of die general contraction type. [Pg.161]

One feature of the Pople basis sets is that they use a so-called segmented contraction. This implies that the primitives used for one basis function are not used for another of the same angular momentum (e.g., no common primitives between the 2s and 3s basis functions for phosphorus). Such a contraction scheme is typical of older basis sets. Other segmented split-valence basis sets include the MIDI and MAXI basis sets of Huzinaga and co-workers, which are named MIDI-1, MIDI-2, etc., MAXI-1, MAXI-2, etc. and vary in the number of primitives used for different kinds of functions. [Pg.172]

For heavier elements primitive basis sets are available, but their contraction is a real art, at least if segmented contractions are used. The use of general contractions is far preferable and is much easier to carry out. [Pg.363]

Results obtained with a larger [5s 3p 2d If] segmented contracted basis axe given in Table 5.13 [89]. The effect of expanding the basis set is to increase the separation for all methods. Since the MRCI(0.025) calculation comprises about six million CSFs it is near the limit of what is currently feasible. The MRCI(O.Ol) calculation would involve over twenty million CSFs, which is impracticably large. Our best directly computed number is probably the MRCI+Q(0.025) result of a little over 5 kcal/mol. We can improve on this estimate by using the small basis results, however. [Pg.387]

Up to now we have assumed that each primitive function is used in the contraction only once, i.e. each primitive function is only involved in one particular contracted function. The contractions of this type are referred to as segmented. In some cases it may occur that for a given primitive set the Dunning s rules suggest a higher number of CGTF s than we intended for a molecular calculation. Con-aider for example the (9s) and (lOs) basis sets of Huzinaga for the first-row atoms. The former contracts satisfactorily to a C4s] set,... [Pg.25]

Segmented contraction of basis sets. 157 Stochastical dynamics, 389 Unperturbed wave function, 123 model, 209 ... [Pg.222]

As discussed previously, FCI calculations for CH2 show that the CASSCF/MRCI treatment accurately accounts for the differential correlation contribution to the CHj Ai- Bi separation. In Table V, this level of treatment is performed using increasingly accurate ANO basis sets. It is interesting to note that although the [4s 3p 2d lf/3s 2p Id] basis set contains fewer contracted functions than the largest segmented basis sets previously applied to this problem, it produces a superior result for the separation. The largest... [Pg.124]

Cao XY, Dolg M (2002) Segmented contraction scheme for small-core lanthanide pseudo potential basis sets. J Mol Struct Theo Chem 581 139... [Pg.171]

F. E. Jorge, A. B. F. da SBva. A Segmented Contraction Methodology for Gaussian Basis Sets to be Used in Dirac-Fock Atomic and Molecular Calculations. Chem. Phys. Lett., 289 (1998) 469 72. [Pg.697]

In the previous discussion of contracted basis functions, the general contraction scheme of Raffenetti, in which every primitive can contribute to every contracted function, was mentioned. The alternate approach produces functions that are sometimes referred to as segmented contractions since the primitives are partitioned into disjoint or almost disjoint sets. Because FORTRAN programs to efficiently implement the general contraction scheme were not very common in the 1960s and 1970s, most basis sets are of the segmented variety. For example, all of the Pople-style basis sets are of this type. [Pg.27]

In implementations which are specialized for segmented basis sets it is usual to scale the integrals with the contraction coefficient in the initial stages of the computation. This simplifies the contraction step to a basic reduction. [Pg.1339]

To give an example, in which the memory access will have a significant effect, consider the first half-transformation step. The following example is a general contraction, for a segmented basis set the transformation step is a simple reduction and should be executed immediately when the primitive integral is formed and resides in the cache. The conventional implementation is... [Pg.1349]

Second-Order Polarization Propagator Approximation (SOPPA) model, 261 Second-order SCF methods, 74 Secular equations, 65, 102 Segmented contraction of basis sets, 157 Self Penalty Walk (SPW) optimization, 330 Self-Consistent Field (SCF), 57, 63 Self-Consistent Reaction Field (SC,RF) models, 393... [Pg.222]


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