Modern versions of CASINO, by contrast, have been shown to exhibit essentially perfect parallel efficiency when accumulating statistical averages on machines with hundreds of thousands of cores in all of its various modes of operation.

If you run the calculations on much more than a thousand cores, then they often start to slow down. Sadly for most popular methods in computational electronic structure – such as density functional theory – this stops being true very quickly as too much interprocessor communication is required. You might expect that if you double the number of processing cores then the code would go twice as fast. The world’s fastest computers now have in excess of a million processor cores, and even your phone probably has at least four.

The man in the street has probably noticed that computers stopped becoming faster because of increasing CPU frequency many years ago, and almost all modern performance improvements are down to increasing parallelism. Because of their inferior scaling with system size, competing methods of comparable accuracy generally struggle to handle more than a few tens of atoms.ĬASINO is also important because QMC is one of the few methods genuinely capable of exploiting the power of modern computer hardware.

These many atoms can form isolated giant molecules or groups of molecules, or they can be the repeating unit in an infinite crystal periodic in one, two, or three dimensions. Other highly accurate methods are known that can do this of course, but what makes CASINO important is that – given a big enough computer – it can carry on doing this for systems containing hundreds or even thousands of atoms. This helps us understand and predict the nature of the Universe (as well as, you know, helping us to design drugs and superconductors and write grant applications). It is capable of calculating incredibly accurate solutions to the Schrödinger equation of quantum mechanics for realistic systems built from atoms. CASINO is a computer program system for performing quantum Monte Carlo (QMC) electronic structure calculations that has been developed by a group of reseachers initially working in the Theory of Condensed Matter group in the Cambridge University physics department, and their collaborators, over more than 20 years.

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