A plane wave implementation of the polarizable continuum model F. De Angelis a , A. Sgamellotti a, * , M. Cossi b , N. Rega b , V. Barone b a Dipartimento di Chimica e Centro di Studio CNR per il Calcolo Intensivo in Scienze Molecolari, Universit  a di Perugia, via Elce di Sotto 8, I-06123 Perugia, Italy b Dipartimento di Chimica, Universit  a Federico II, via Mezzocannone 4, I-80134 Napoli, Italy Received 20 June 2000; received in ®nal form 11 August 2000 Abstract We have implemented the polarizable continuum model for solute±solvent interactions into a plane-wave (PW) Car± Parrinello code. A comparison between PW and Gaussian-type orbitals (GTO) basis sets implementations, concerning solvation energies and dipole moments of a number of small systems, is reported. All the computations have been performed using the BPW91 exchange-correlation functional. GTO calculation has been performed using the 6-311G(d,p) basis set for geometry optimizations, and the aug-cc-pVTZ basis for energies and dipole moments. PW calculations were carried out on the Gaussian optimized geometries, up to an energy cuto of 30 Ry. Excellent agreement between PW and GTO calculations is obtained, with average deviations of solute±solvent interaction energies lower than 0.5 kcal/mol. Ó 2000 Elsevier Science B.V. All rights reserved. 1. Introduction Theoretical and computational chemistry pres- ently face the very demanding challenge of ex- panding the applicability of quantum-mechanical (QM) approaches to large systems in condensed phases. In this context, the situation is particularly favorable for Kohn±Sham (KS) methods [1], which can be implemented using either atom- centered functions [1] or plane waves (PW) for expanding KS orbitals [2,3]. An appealing feature of PWs is that they allow the use of fast Fourier transform (FFT) techniques, which are computa- tionally very ecient and have good scaling properties. PWs are also free of basis set super- position errors, and their convergence can be controlled in a very simple way, since it depends only upon the number of Fourier components in- cluded in the expansion of the KS orbitals. The disadvantage of PWs is, of course, their slow convergence for the description of localized orbi- tals, which calls for the use of pseudopotentials for the description of core states. From another point of view, while the explicit inclusion of solvent molecules in numerical simu- lations is providing interesting results [4±6], con- tinuum solvent models are becoming more and more eective and reliable, thanks to the increas- ing accuracy of the underlying model coupled with signi®cant ¯exibility and eciency [7,8]. In par- ticular, thanks to a number of recent improve- ments, the dierent variants of the so-called 29 September 2000 Chemical Physics Letters 328 (2000) 302±309 www.elsevier.nl/locate/cplett * Corresponding author. Fax: +39-75-585-5606. E-mail address: sgam@thch.unipg.it (A. Sgamellotti). 0009-2614/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 9 - 2 6 1 4 ( 0 0 ) 0 0 9 5 2 - 0