An efficient procedure for calculating the molecular gradient, using SCF-CI semiempirical wavefunctions with a limited number of configurations

Dewar, Michael J. S.; Liotard, D.

doi:10.1016/0166-1280(90)85012-c

Cited by 48 publications

(23 citation statements)

References 26 publications

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“…In MNDOC, these are found by finite difference, a very time-consuming procedure. Since this difficulty does not arise in our AMPAC program where derivatives of the CI wave function are calculated analytically, using a new algorithm due to Liotard [35], an analogous version of AM^, or of our new procedure, could easily be developed.…”

Section: (A) Theoretical Values For Integralsmentioning

confidence: 99%

The semiempirical approach to chemistry

Dewar¹

1992

Int J of Quantum Chemistry

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Two kinds of quantum mechanical treatment are needed in chemistry: First, a treatment accurate enough to provide definitive solutions of chemical problems, in particular, the prediction of reactions and reaction mechanisms, without reference to experiment. As yet, treatments of this degree of accuracy are restricted to a few small atoms and molecules. Second, a treatment that chemists can use as a practical aid to their own research, on the same basis as mass spectrometry or NMR. Here, the need has been largely met by the series of progressively better semiempirical methods, in particular, those developed by our group. Since only the best and most expensive ab initio procedures are superior to ours and since the computing time they need is far greater, their use as a practical aid in chemistry is restricted. Our procedures, therefore, serve as a useful supplement to ab initio ones in areas where the latter cannot be applied effectively, as the leading ab initioists now fully recognize. Since the semiempirical approach is capable of almost unlimited further development, this situation is likely to continue in the foreseeable future. 0 1992 John Wiley & Sons, Inc.

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Section: (A) Theoretical Values For Integralsmentioning

confidence: 99%

The semiempirical approach to chemistry

Dewar¹

1992

Int J of Quantum Chemistry

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“…Gradient methods, even in their crudest forms [16,17], are definitely better when n exceeds 10 or 20. Analytical formulations of the gradient [18], now fast and accurate within semiempirical SCF or SCF-CI schemes [5,6], reinforce the tendency.…”

Section: Energy Minimization By Gradient Methodsmentioning

confidence: 89%

“…During the last 5 years, the AMPAC code has strongly evolved. The implementation of an analytical computation of the gradient [5] provides a speedup by two orders of magnitude on supercomputers [6]. This offers new possibilities in the study of potential surfaces and the arsenal of methods has been reinforced [7].…”

Section: Introductionmentioning

confidence: 99%

Algorithmic tools in the study of semiempirical potential surfaces

Liotard

1992

Int J of Quantum Chemistry

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The most efficient optimization methods implemented in the semiempirical package AMPAC are presented. They concern the minimization of the energy or of the gradient norm by either pseudo-Newton or quadratic procedures, the search for transition states, and the intrinsic reaction coordinate in conjunction with variational transition-state theories. Nonlocal methods such as simulated annealing are also introduced. 0 1992 John Wiley & Sons, Inc.

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“…67 The geometries of 1,4-dioxane and 18-crown-6 were optimized at the SCF level. These compounds have been used as models previously by Dewar and Liotard 48 and Izzo and Klessinger. 49 Our computation times (CPU times in seconds on an 833 MHz Alpha workstation) are listed in Tables 3 and 4.…”

Section: Performance and Applicationsmentioning

confidence: 99%

“…43,44 Analytic CI gradients have been implemented by other groups in an ab initio GUGA-CI framework. 14,[45][46][47] In the context of semiempirical methods, gradients have been reported for small SCF-CI expansions, 48 MNDOC-MRCI wave functions, 49 and CI wave functions with floating occupation molecular orbitals. 50 This article is organized as follows.…”

Section: Introductionmentioning

confidence: 99%

Implementation of a general multireference configuration interaction procedure with analytic gradients in a semiempirical context using the graphical unitary group approach

2003

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The graphical unitary group approach has been applied in an efficient implementation of a general multireference configuration interaction (MRCI) method for use with small active molecular orbital spaces in a semiempirical framework. Gradients can be computed analytically for molecular orbitals from a closed-shell or a half-electron open-shell Hartree-Fock calculation. CPU times for single point energy and gradient calculations are reported. The code allows MRCI geometry optimizations of large molecules, as illustrated for the singlet ground state and the four lowest triplet states of fullerene C(76).

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An efficient procedure for calculating the molecular gradient, using SCF-CI semiempirical wavefunctions with a limited number of configurations

Cited by 48 publications

References 26 publications

The semiempirical approach to chemistry

The semiempirical approach to chemistry

Algorithmic tools in the study of semiempirical potential surfaces

Implementation of a general multireference configuration interaction procedure with analytic gradients in a semiempirical context using the graphical unitary group approach

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