Reduced-Size Polarized Basis Sets for Calculations of Molecular Electric Properties. I. The Basis Set Generation ZUZANA BENKOVA, 1, * ANDRZEJ J. SADLEJ, 1 ROMA E. OAKES, 2 STEVEN E. J. BELL 2 1 Department of Quantum Chemistry, Institute of Chemistry, Nicolaus Copernicus University, 7, Gagarin St., PL-87 100 Torun ´, Poland 2 The School of Chemistry, The Queen’s University of Belfast, Belfast BT9 5AG, UK Received 29 July 2004; Accepted 27 September 2004 DOI 10.1002/jcc.20149 Published online in Wiley InterScience (www.interscience.wiley.com). Abstract: Following the recent studies of basis sets explicitly dependent on oscillatory external electric field we have investigated the possibility of some further truncation of the so-called polarized basis sets without any major deterioration of the computed data for molecular dipole moments, dipole polarizabilities, and related electric properties of molecules. It has been found that basis sets of contracted Gaussian functions of the form [3s 1p] for H and [4s 3p1d] for the first-row atoms can satisfy this requirement with particular choice of contractions in their polarization part. With m denoting the number of primitive GTOs in the contracted polarization function, the basis sets devised in this article will be referred to as the ZmPol sets. In comparison with earlier, medium-size polarized basis sets (PolX), these new ZmPol basis sets are reduced by 2/3 in their size and lead to the order of magnitude computing time savings for large molecules. Simultaneously, the dipole moment and polarizability data remain at almost the same level of accuracy as in the case of the PolX sets. Among a variety of possible applications in computational chemistry, the ZmPolX are also to be used for calculations of frequencies and intensities in the Raman spectra of large organic molecules (see Part II, this issue). © 2004 Wiley Periodicals, Inc. J Comput Chem 26: 145–153, 2005 Key words: polarized basis sets; ZmPolX basis sets; dipole moments; dipole polarizabilities Introduction It is well recognized that in molecular electronic structure calcu- lations based on the idea of the single-particle approximation, the success is mostly determined by the choice of basis functions. 1,2 The large all-purpose basis sets that have been developed in recent years by Dunning and coworkers, 3–5 are currently considered to be the best choice for highly accurate and systematic studies of energies and properties of atoms and molecules. 2 In addition they can be used to study the convergence to the complete basis set limit at the given level of approximation. Despite all the advantageous features of the correlation-consis- tent sets of Dunning et al., 3–5 their use in molecular calculations is, in practice, limited to relatively small systems. The core and disk space requirements and the timing of calculations with these sets become prohibitively large already for moderate values of the so-called basis set cardinal number. 3 On the other hand, the small- est basis sets of this series, that is, the cc-pVDZ 3 and aug-cc-pVDZ sets, 4 are usually too small to give sufficiently accurate results for molecular properties and their geometry derivatives. A remedy to this problem can be found among purpose-oriented (property- oriented) basis sets, that is, basis sets of moderate size that are specifically tailored for the calculation of some selected molecular properties. A general strategy for the generation of relatively small pur- pose-oriented basis sets can be based on the optimization of their size and parameters with respect to some selected properties. There is also a considerable amount of experience gained in earlier investigations that permits us to devise moderately sized basis sets for particular purposes (see, e.g., ref. 6). To be successful, the brute-force optimization methods need to be based on some vari- ation principle, and are rather costly. However, the educated guess approaches lead to basis sets that are usually devised for the study of particular features of some selected molecule. 7 A convenient and fairly general method for the generation of property-oriented basis sets can be based on simple physical mod- els that determine the basis set dependence on the perturbation Correspondence to: S. J. Bell; e-mail: S.bell@qub.uk *Permanent address: Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University, Mlynska dolina, SK-84215 Bratislava, Slovakia © 2004 Wiley Periodicals, Inc.