Improvements of Parametric Quantum Methods with New Elementary Parametric Functionals FERNANDO RUETTE, 1 STEFANIA A. M. MARCANTOGNINI, 2 VALENTIN V. KARASIEV, 3 MORELLA SA ´ NCHEZ 1 1 Laboratorio de Quı ´mica Computacional, Centro de Quı ´mica, Apartado 21827, Caracas, Venezuela 2 Departamento de Matema ´ticas, IVIC, Apartado 21827, Caracas, Venezuela 3 Laboratorio de Fı ´sico-Quı ´mica Teo ´rica, Centro de Quı ´mica, Apartado 21827, Caracas, Venezuela Received 19 October 2007; accepted 12 February 2008 Published online 18 April 2008 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/qua.21669 ABSTRACT: A series of elementary parametric functionals (EPFs) for resonance integral, electron-electron repulsion, electron-nucleus attraction, core-core interaction, and bond correlation correction were included in the new version of CATIVIC method [Int J Quantum Chem 2004, 96, 321]. In the present work, a systematic way to improve the precision of parametric quantum methods (PQMs) by using several EPFs in the parameterization of a set of molecules is proposed. Based on the fact that a linear combination of elementary functionals from the exact Hamiltonian is also a functional, a linear combination of EPFs has been proved that can enhance the accuracy of PQMs by considering the convex condition. A general formulation of simulation techniques for molecular properties is presented and a formal extension of the minimax principle to PQMs is also considered. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem 108: 1831–1839, 2008 Key words: parametric quantum method; parametric functional; CATIVIC; quantum software; semiempirical method 1. Introduction Q uantum chemistry modeling has been taking recently technological importance due to the option of designing new substances based on more efficient theoretical tools enable to predict proper- ties of adequate materials for the industry. Actual trends suggest that the future of technological achievements is in the area of nanotechnology, which shows a vertiginous growth without prece- dent nowadays. In the field of electronic devices, small feature sizes result in increased functionality, faster speed, lower costs in microelectronic process- ing power and dimension of dynamic memories. On the other hand, in the area of industrial chem- istry, the synthesis of fashionable catalytic nanopar- ticles means a high activity and selectivity in the Correspondence to: F. Ruette; e-mail: fruette@ivic.ve International Journal of Quantum Chemistry, Vol 108, 1831–1839 (2008) © 2008 Wiley Periodicals, Inc.