A simple mathematical correction can cure one of computational chemistry's biggest problems and massively improve the study of many-molecule systems, say Tobias Schwabe and Stefan Grimme at the University of Münster, Germany.

Density functional theory (DFT) is a way of calculating the electronic structure of many-molecule systems, in order to predict their behaviour and properties. It is a very popular approach to computational chemistry, but one of its shortcomings is that it does not take into account weaker inter-molecular interactions such as van der Waals forces. Van der Waals forces play an essential role in many chemical and biological systems, influencing everything from crystal formation to the way geckos stick to walls. 'These effects become increasingly important when larger molecular systems are investigated, for example in the nanosciences, but so far have mostly been overlooked,' said Grimme.

Schwabe and Grimme's method builds on a so-called double-hybrid DFT model, designed as a starting point for studying interactions between electrons in large systems. 'The accuracy of the original double-hybrid DFT was already very good, but careful analysis of the failures revealed an incomplete account of van der Waals effects,' said Grimme. 

Simply by adding an extra term to the equation, the pair have massively improved the accuracy of DFT and brought it up to a standard sufficient for the study of complicated biological and nanoscale systems, extending the range of problems to which it can be applied. The simplicity of the correction makes it useful for a wide range of problems and day-to-day computations, said Grimme.

'The new method now holds several "world records" for best performance of DFT for important chemical problems such as heat of formation, van der Waals complexation and protein folding,' he added.

Clare Boothby