Special Issue Preface pubs.acs.org/JPCA
Tribute to Jacopo Tomasi Jacopo’s first research works, under the guidance of Professor Scrocco, concerned quantum chemistry methods, as the times required: use of different kinds of basis sets in nonempirical quantum mechanical computations, implementation of more effective Hartree−Fock schemes, and just after, configuration interaction expansions. Very soon, one of the more distinctive features of Jacopo’s research philosophy started to emerge, namely the direct confrontation and cross-fertilization with experimentally oriented chemists. The first example of this attitude is the determination of nuclear quadrupole coupling constants, in close correspondence with the development of nuclear quadrupole resonance spectroscopy in Pisa. At the same time, interpretation and analysis of the results for molecular systems of increasing complexity required, and still requires, the development of theoretical concepts and tools, able to extend the range of applicability of nonempirical calculations and to extract from their results at least semiquantitative information about structural, thermodynamic, kinetic, and spectroscopic properties. A general strategy, consisting of two main points, is already apparent in the most significant publications since the late 1960s and was explicitly stated later on. The first aspect is related to the practical impossibility of “‘brute force”’ ab initio computations for larger and larger systems due to the unfavorable scaling of these techniques with the number of electrons. At the same time, simplified (e.g., semiempirical) models are dangerous because they unavoidably imply poorly controlled approximations and some fitting to a reduced number of properties and/ or molecular systems. Sharing the general point of view of some of the most influential theoretical chemists of his generation, Jacopo was led to the selection and development of the socalled focused models in which the core features are treated at the highest level of accuracy, and other important but complementary aspects are taken into account in a less detailed way. The second basic observation is that performing more and more computations could add little to our knowledge, if general rules could not be formulated and validated together with distinctive trends and well sound concepts helping us to understand and predict chemical phenomena at a qualitative or semiquantitative level. The alternative to this continuous and hard effort toward generalization, validation, and interpretation is the transformation of theoretical chemistry into “a deluge of numbers on a desert of concepts”, to quote a colorful expression due to Bernard Levy. One of the first remarkable results along these lines came from a systematic exploration, in the 1970s and early 1980s, of the predictive power of the molecular electrostatic potential (MEP) for chemical reactivity and intermolecular interactions. He developed an early version of what we would now call a quantum mechanical/molecular mechanics method, demonstrated the additivity of group contributions to the MEP, and investigated the validity of energy and wave function
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acopo Tomasi was born in Diano Marina, a sea town in the northwest of Italy, on 14 September 1934. During his youth he went through the harshness and upheaval of World War II, and to this period belong the first reminiscences we share of hisoccasionally dangerousadventures: mother cooking with TNT, for lack of a tamer fuel; or young Jacopo following his father into a minefield to gather firewood. This is just the first of several “adventures” he likes to share with his friends by means of a natural inclination to entertaining talks. Surely this quality was reinforced by his perennial curiosity for a very broad class of philosophical, artistic, and of course, scientific interests always cultivated by travels, lectures, and discussions. A broad range of scientific (and extra-scientific) interests, an enviable memory, and very effective organization of bibliographic work make him an exceptionally cultured chemist. In 1952, Jacopo won a scholarship from the Scuola Normale Superiore and moved to Pisa to study chemistry. It was a very fruitful period: the Institute of Chemistry underwent a big renovation thanks to the incisive and innovative impulse of two leading figures, Eolo Scrocco and Piero Pino. Moreover, the issue of electronic computers exploded and in Italy, the leadership of this new sector was taken by Pisa University: following the advice of Enrico Fermi, professors and technicians designed and built the first electronic computer in Italy, the “Calcolatrice elettronica Pisana”, which became operative in 1960. With the availability of the Calcolatrice elettronica Pisana, Jacopo and other young researchers, together with their senior fellows in theoretical chemistry entered the era of electronic computing, after years of painstaking calculations with crank calculators and handwritten equations, integrals, and matrix operations. © 2015 American Chemical Society
Special Issue: Jacopo Tomasi Festschrift Published: May 28, 2015 5039
DOI: 10.1021/acs.jpca.5b03906 J. Phys. Chem. A 2015, 119, 5039−5040
The Journal of Physical Chemistry A
Special Issue Preface
as a younger researcher working in Naples, but collaborating with the Jacopo’s group, was strongly influenced by his personality, political and scientific rigor, and kindness. We shared several points of view, and in particular the idea, not very popular at least in Europe even in the 1990s, of making our developments freely available to a large community of users by means of implementation in widely employed packages. In more general terms, the number and quality of the contributions collected in this special issue dedicated to the 80th birthday of Jacopo Tomasi witness in the best way the role he played in theoretical and computational chemistry. We are very grateful to the many colleagues who authored the different papers, and to the numerous referees who have dedicated their valuable time to evaluate the manuscript. We are also grateful to Anne McCoy for her enthusiastic acceptance of our proposal for this special issue and to the whole JPC staff.
decomposition schemes in intramolecular and intermolecular interactions. The quest for simplified models and qualitative explanations is also apparent in the intense work on chemical reactivity and in the first investigations on excited states, which triggered interest in photochemistry among younger coworkers in Pisa. Of this period, the most lasting success is certainly the introduction of the MEP as a tool for characterizing the reactivity of functional groups, enzyme active sites, host−guest and solute−solvent interactions, crystal surfaces, and cavities. Starting from the first paper in 1981, the central activity of Jacopo in the next decades is characterized by the systematic development, validation, and application of the polarizable continuum model (PCM), which has revolutionized the scope of computational chemistry, allowing us to perform investigations of systems in solution with essentially the same accuracy and computational cost of the corresponding computations for isolated molecules. Although the PCM formulation was not the first based on an effective Hamiltonian and on the representation of the solvent as a continuum dielectric, its strength is the use of a solvent cavity of realistic shape and of the true electrostatic potential (or electric field) without any multipolar development. This led to a wider applicability than previous continuum models, but to a more difficult implementation of analytical derivatives, which was finally achieved starting from 1994. The implementation of the model itself was re-formulated several times significantly improving generality, effectiveness, and, in the last years, smoothness of the computed free energy surface. Because the main features of the “PCM story” are reviewed directly by Jacopo in his extended autobiography also present in this issue, I only recall that the last years of Tomasi’s scientific activity have been devoted to the extension of the PCM to timedependent solvation, molecular properties, and spectroscopies and on approaches to couple continuum and discrete models. Such extensions permit us nowadays to obtain calculated values remarkably matching their experimental counterparts. In parallel, some work has also been done on the extension of continuum models to treat complex condensed phases, such as ionic solutions, anisotropic dielectrics, heterogeneous systems, liquid−gas and liquid−liquid interfaces and molecules closed to metal nanoparticles. Such works have permitted us to enlarge the range of possible applications of continuum solvation approaches and to treat phenomena, which are predominantly the prerogative of computer simulations. The research group of Jacopo has never been very large, but looking at the list of his publications, we can deduce that he has worked with more than 100 other scientists, many of them young people and mostly foreigners. They carried with them new ideas and interests, different points of view and technical skills, and the sharing of these experiences enriched the work of the Pisa quantum chemists. To many of these people Jacopo has been “the boss”, for a few months or for several years, in his peculiar way. Feeling like his responsibility, he has always done his best to allow his collaborators to do research (and teaching and other academic duties) according to his or her skill and aptitude. At the same time, he has always supported and encouraged everybody who wished to develop a new research line, although far from the “core business” of the group. Let us recall also the impact Jacopo had on the formation of several generations of Italian and foreign theoretical chemists with special attention to people working in southern and eastern Europe together with Latin America. One of us (V.B.),
Vincenzo Barone
Scuola Normale Superiore
Keiji Morokuma Kyoto University
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DOI: 10.1021/acs.jpca.5b03906 J. Phys. Chem. A 2015, 119, 5039−5040
