GaussMem – ZX Spectrum Edition

Winner of the Pascalated Basic Contest 2022 in the Category B.

Gaussian is a very popular suite of commercial software for computational chemistry aimed at electronic structure quantum-mechanical calculations. This type of calculations is extremely demanding from a computational point of view. Even evaluating the electronic structure of a small molecule can require the computation of millions of integrals.

Gaussian, in its current version G16 C.01, can run on a variety of systems, ranging from single-core computers to supercomputers such as Galileo100 and Marconi100 at CINECA. The applications of computational chemistry are extremely varied, ranging from the development of novel materials and drugs, to the understanding of biochemical processes, to the investigation of the mechanism of restoration agents for Cultural Heritage. 

The computational capability of Gaussian is allowed by the possibility to cope with a large number of cores and memory. In this context, the evaluation of the correct amount of memory is crucial. In fact, a shortage of assigned memory will prevent all cores to be used, while increasing excessively the amount of memory will cause the calculation to slow down significantly.

The required amount of memory depends on the following parameters:

• The number of assigned processors.
• The type of calculations.
• The basis set, i.e. the library of mathematical functions describing the electron shells of the investigated system.

The amount of memory is provided to Gaussian in several units, such as megawords (1 MW = 1,048,576 words = 8,388,608 bytes), megabytes (MB), or gigabytes (GB). For example, on a 64-bit single-core system, a 300 basis function Hartree-Fock optimization of the geometry of a molecule using g functions would require 10.4 MW (about 83 MB).

The evaluation of the required memory is not trivial, since it is given by a memory threshold augmented by a term linearly proportional to the square of the number of basis functions. GaussMem is currently available for a variety of OSs (link).  

GaussMem – ZX Spectrum Edition brings a professional research tool for evaluating the memory required for Gaussian calculations to the humble ZX Spectrum. This computational tool is particularly useful to theoretical chemists, as shown by the number of times questions on the use of memory in Gaussian have appeared on specialized social media, such as ResearchGate. Worthy of note, a snapshot of GaussMem can be easily embedded in a self-running sandbox for Windows, Linux, or macOS systems adopting a variety of available emulators.

In this 2023 release, GaussMem has now been converted to Boriel ZX Basic to provide a quicker, smarter, and fastest version, ready to be downloaded and executed on an authentic ZX Spectrum, ZX Spectrum Next,  or any emulator.

Distribution. GaussMem is completely free and can be unreservedly distributed, provided that it is not modified in any way and that the relevant files are accompanied by this text.

Citation. In case GaussMem would be used for scientific publication purposes, the authors are kindly requested to cite the following paper, where GaussMem is reported (Experimental):

(a) M. C. Aragoni, E. Podda, S. Chaudhary, A. K. K. Bhasin, K. K. Bhasin, S. J. Coles, J. B. Orton, F. Isaia, V. Lippolis, A. Pintus, A. M. Z. Slawin, J. D. Woollins, M. Arca, "An Experimental and Theoretical Insight into I₂/Br₂  Oxidation of Bis(pyridin-2-yl)Diselane and Ditellane",  Chem. – Asian J.  2023, e202300836. DOI: doi.org/10.1002/asia.202300836

(b) M. Arca, GaussMem ZX Spectrum Edition, https://massimiliano-arca.itch.io/gaussmem-zx-spectrum-edition .