Theoretical chemistry developments: from electronic structure to simulations

Only two decades ago many experimental chemists often considered theoretical chemistry as a “superfluous oddity” or at most as a “nice gimmick” with limited relation to the realities of chemical research. Today, this situation has drastically changed and quantum theory plays an eminent role in almost all branches of chemistry. Indeed, nowadays the majority of chemical publications contain at least a paragraph or a section describing computational chemistry calculations. Consequently, theoretical chemistry has evolved into a vast array of subdisciplines, ranging from electronic structure theory to classical molecular dynamics or coarse grained simulations. Each of these subdisciplines has their own agenda and their own scientific culture that are often fairly disjointed. For example, while solid state electronic theory and molecular electronic structure theory have many fundamental commonalities, they employ very different vocabulary for related quantities and differ radically with respect to how they approach experimental reality.

It is probably fair to say that theoretical chemistry has found a prominent place in chemistry as a reliable standard tool but it has also leaped into many of the neighboring disciplines of biology and physics. The systems which can be treated today are getting larger and larger. They encompass hundreds of atoms at the electronic structure level and hundreds of thousands of atoms in classical simulations. There are enormous challenges associated with such large-scale calculations. These challenges range from mere computational bottlenecks to challenges with the accuracy of the predictions and from conformational complexity inherent in large systems to problems of interpretation. Thus, more complexity than ever is nowadays the central focus of theoretical chemistry methods.

Nevertheless, theoretical chemistry is not a static science that has arrived at its “final state” in which its primary goal is to serve the neighboring disciplines, but it is a mature scientific field with its own agenda that is to some extent independent of the requests and needs of experimentalists. In fact, a great deal of progress has been made in recent years in all areas of theoretical chemistry. This progress is not just related to progress with computational hardware, but is largely conceptual. For example, much more accurate calculations than envisioned a decade ago are now commonplace, much larger calculations are possible, much more information can be extracted from the calculations using advanced analysis tools and much longer timescales can be reached in simulations.

Thus, it is timely to present a dedicated issue of PCCP to the general public. In bringing together the contributions to this issue we have paid particular, but not exclusive, attention to giving the younger generation of theoretical chemists a forum. That is, we wanted to bring the scientists together that will shape the future of the discipline, the scientists that will think outside the box and will be able to eventually transcend the traditional boundaries of the discipline. We intended the issue to be broad in its scope in order to highlight the enormous intellectual and methodological richness of the field. It is in the nature of such an attempt that the selection of scientists was subjective and that not all candidates could make the commitment. However, we are extremely excited by the contributions that are contained in this issue which reflect the depth and diversity that is so characteristic of the field of theoretical chemistry. The contributions range from the analysis of deep conceptual problems in relativistic quantum chemistry (e.g. Shiozaki et al.) to questions of interpretation (Mathews et al.) to approaches designed to treat the largest of systems (Roemer). The contributions certainly reflect the trend to strive for higher and higher accuracy in both electronic structure (Ayers et al., Friedrich et al., Shiozaki et al., Hochlaf et al.) as well as molecular dynamics simulations (Kuhne et al., Salanne). There is also a clear trend to strive for a closer marriage between theory and experiment (Rulisek et al., Menucci et al., Hochlaf et al., Mathews et al., Evangelista et al.), to treat ever larger systems (Golze et al., Neugebauer et al., Ngyen et al., Roemer), to translate quantum chemical results into a chemical language (Guihery et al., Gonzalez et al., Mathews et al.) and to validate the results of calculations against higher level theoretical methods (Blumberger et al., Hochlaf et al., Guihery et al.).

Overall, we are extremely excited about this issue of PCCP and we hope that readers of the journal will be able to appreciate how much momentum there is in the field of theoretical chemistry. The future perspectives for an even closer integration of theory into chemistry look bright indeed!

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