Distributed universal even-tempered basis set

Systematic Trancation of a Distributed Universal Even-Tempered Basis Set of Gaussian Functions an Application to the Ground State of the BF Molecule... 

In this paper, the systematic truncation of a distributed universal even-tempered basis set capable of supporting high precision in both mauix Haitree-Fock and second order many-body perturbation theory calculations is explored using the ground state of the boron fluoride molecule as a prototype. The truncation procedure adopted is based on the magnitude of the orbital expansion coefficients associated with a given basis function in each of the occupied orbitals. 

Truncation of a Distributed Universal Even-tempered Basis Set... 

A distributed universal even-tempered basis set for the boron fluoride ground state [24] is employed in the exploratory calculations reported here. This basis set is capable of... 

Table 7 Total matrix Hartree-Fock energies calculated with truncated distributed universal even-tempered basis sets comparison with the finite difference Hartree-Fock energy and the matrix Hartree-Fock energy supported by the basis set before truncation. The energies are given in Hartree energy differences, which are defined in the text, are given in pHartree...

Systematic truncation of a distributed universal even-tempered basis set of 323 Gaussian functions an application to the ground state of the BF molecule... 

Btiilding on atomic studies using even-tempered basis sets, universal basis sets and systematic sequences of even-tempered basis sets, recent work has shown that molecular basis sets can be systematically developed until the error associated with basis set truncation is less that some required tolerance. The approach has been applied first to diatomic molecules within the Hartree-Fock formalism[12] [13] [14] [15] [16] [17] where finite difference[18] [19] [20] [21] and finite element[22] [23] [24] [25] calculations provide benchmarks against which the results of finite basis set studies can be measured and then to polyatomic molecules and in calculations which take account of electron correlation effects by means of second order perturbation theory. The basis sets employed in these calculations are even-tempered and distributed, that is they contain functions centred not only on the atomic nuclei but also on the midpoints of the line segments between these nuclei and at other points. Functions centred on the bond centres were found to be very effective in approaching the Hartree-Fock limit but somewhat less effective in recovering correlation effects. 

In our previous work [15-22], we have used a universal sequence of distributed even-tempered basis set in which the exponents for each symmetry type form a geometric series according to the formula tk = on each expansion centre. Different parameters a and fi were used for the functions of x-type in order to provide the additional flexihility required to obtain a satisfactory description of any cusp at the point upon which the functions were centred. Common values of a and /3 were used for p-type functions and functions of higher symmetry. The orbitals, both occupied and unoccupied, are then approximated by an expansion of the form... 

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