George Fitzgerald

Bio: George Fitzgerald is an academic researcher from Symyx Technologies. The author has contributed to research in topics: Density functional theory & Ab initio. The author has an hindex of 30, co-authored 59 publications receiving 4265 citations. Previous affiliations of George Fitzgerald include University of California, Berkeley & Lawrence Berkeley National Laboratory.

Molecular gradients and hessians implemented in density functional theory

Abstract: We derive expressions for molecular gradients and hessians for the case when the energy is evaluated using density functional theory. Although derivative expressions have been proposed previously, our derivation is based on the unitary exponential parameterization of the wavefunction, and our expressions are valid for local and non–local potentials. Density functional theory, although similar in implementation to standard SCF theory, differs in that it introduces an exchange–correlation term which is density dependent. The presence of such a quantity introduces additional derivative terms which are not present in standard approaches of electronic structure theory. Expressions are derived for both the exact Coulombic repulsion, as well as the case where the density is expressed as a fitted quantity. Given these choices our final equations offer a computationally tractable expression with particular emphasis on conditions which ensure that the computed quantities are numerically correct. We show that althou...

Electronic Structures and Geometries of C60 Anions via Density Functional Calculations

Abstract: The geometries and electronic structures of C60 and its mono- through hexaanions, all of which have been prepared in macroscopic quantities, are calculated using modern density functional techniques. Clear assignments of the electronic states, symmetries, and Jahn−Teller distorted geometries of the ions, which are difficult to determine experimentally, are obtained. The results are compared with available experimental data, and the agreement is excellent. Our calculations predict the geometries and electronic structures which have not yet been measured. Comparison with previous theoretical work indicates that density functional theory is the method of choice for the fullerene anions.

Accurate Coulomb-fitting basis sets for H to Rn

Abstract: A series of auxiliary basis sets to fit Coulomb potentials for the elements H to Rn (except lanthanides) is presented. For each element only one auxiliary basis set is needed to approximate Coulomb energies in conjunction with orbital basis sets of split valence, triple zeta valence and quadruple zeta valence quality with errors of typically below ca. 0.15 kJ mol−1 per atom; this was demonstrated in conjunction with the recently developed orbital basis sets of types def2-SV(P), def2-TZVP and def2-QZVPP for a large set of small molecules representing (nearly) each element in all of its common oxidation states. These auxiliary bases are slightly more than three times larger than orbital bases of split valence quality. Compared to non-approximated treatments, computation times for the Coulomb part are reduced by a factor of ca. 8 for def2-SV(P) orbital bases, ca. 25 for def2-TZVP and ca. 100 for def2-QZVPP orbital bases.

A Chemist's Guide to Density Functional Theory

Abstract: "Chemists familiar with conventional quantum mechanics will applaud and benefit greatly from this particularly instructive, thorough and clearly written exposition of density functional theory: its basis, concepts, terms, implementation, and performance in diverse applications. Users of DFT for structure, energy, and molecular property computations, as well as reaction mechanism studies, are guided to the optimum choices of the most effective methods. Well done!" Paul von RaguE Schleyer "A conspicuous hole in the computational chemist's library is nicely filled by this book, which provides a wide-ranging and pragmatic view of the subject.[...It] should justifiably become the favorite text on the subject for practioneers who aim to use DFT to solve chemical problems." J. F. Stanton, J. Am. Chem. Soc. "The authors' aim is to guide the chemist through basic theoretical and related technical aspects of DFT at an easy-to-understand theoretical level. They succeed admirably." P. C. H. Mitchell, Appl. Organomet. Chem. "The authors have done an excellent service to the chemical community. [...] A Chemist's Guide to Density Functional Theory is exactly what the title suggests. It should be an invaluable source of insight and knowledge for many chemists using DFT approaches to solve chemical problems." M. Kaupp, Angew. Chem.

Optimization of equilibrium geometries and transition structures

Abstract: A modified conjugate gradient algorithm for geometry optimization is outlined for use with ab initioMO methods. Since the computation time for analytical energy gradients is approximately the same as for the energy, the optimization algorithm evaluates and utilizes the gradients each time the energy is computed. The second derivative matrix, rather than its inverse, is updated employing the gradients. At each step, a one-dimensional minimization using a quartic polynomial is carried out, followed by an n-dimensional search using the second derivative matrix. By suitably controlling the number of negative eigenvalues of the second derivative matrix, the algorithm can also be used to locate transition structures. Representative timing data for optimizations of equilibrium geometries and transition structures are reported for ab initioSCF–MO calculations.

A second order multiconfiguration SCF procedure with optimum convergence

Abstract: An MCSCF procedure is described which is based on the direct minimization of an approximate energy expression which is periodic and correct to second order in the changes in the orthonormal orbitals Within this approximation, the CI coefficients are fully optimized, thereby accounting for the coupling between orbital rotations and CI coefficients to higher order than in previous treatments Additional transformations among the internal orbitals and their associated one‐ and two‐electron integrals are performed which amounts to treating the rotations among internal orbitals to higher than second order These extra steps are cheap compared to the four index transformation performed in each iteration, but lead to a remarkable enhancement of convergence and overall efficiency In all calculations attempted to date, convergence has been achieved in at most three iterations The energy has been observed to converge better than quadratically from the first iteration even when the initial Hessian matrix has many negative eigenvalues

Advances in methods and algorithms in a modern quantum chemistry program package

Abstract: Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package, together with illustrative timings and applications. Specific developments discussed include fast methods for density functional theory calculations, linear scaling evaluation of energies, NMR chemical shifts and electric properties, fast auxiliary basis function methods for correlated energies and gradients, equation-of-motion coupled cluster methods for ground and excited states, geminal wavefunctions, embedding methods and techniques for exploring potential energy surfaces.