Heavy Molecules Made Easy: ECPs and QEC 2.0

How do scientists study complex molecules, especially those with heavy atoms? It’s a challenge of immense scale. The sheer number of electrons makes a complete calculation computationally intensive and often impractical.  This is a core challenge in quantum chemistry, and it’s precisely where a clever solution called Effective Core Potentials (ECPs) comes into play. 

The Problem with Heavy Atoms 

Imagine a molecule like silicon tetraiodide (SiI4​). It has one silicon atom and four iodine atoms. The iodine atoms are the real “heavyweights” here. A single iodine atom has 53 electrons. Multiply that by four, and you’re looking at a molecule with a total of 226 electrons!

Trying to calculate the behavior of every single one of these electrons is a massive undertaking – it could require hours or days to run, even on a supercomputer. Traditionally, we need to account for all electrons using complex quantum mechanical equations, which poses a huge computational challenge. However, most of the interesting chemical activity only happens in a small subset of the overall electronic space – the valence shell. As a result, most of the computational run time is ‘wasted’ representing inner-shell electrons that are chemically inactive, and therefore not worth treating with highly accurate methods. Despite their lack of chemical activity, inner-shell electrons add immense computational overhead to quantum chemical calculations, often making larger atoms such as iodine too complex to handle.

A Smarter Way: The ECP Solution 

So, what’s the solution? We use ECPs, or Effective Core Potentials. Instead of trying to keep track of every single core electron, ECPs treat the nucleus and its core electrons as a single, simplified unit. 

This ‘potential’ effectively models the influence of the core on the outer, or valence, electrons, which are the ones we are really interested in from a chemistry perspective.

By using ECPs, the computational problem is dramatically simplified. For our SiI4 ​ example, we replace the 46 core electrons from each of the four iodine atoms with ECPs. This reduces the total number of electrons we need to explicitly calculate from 226 to just 42! That’s a huge difference that makes complex calculations possible on standard computers.

Enter QEC 2.0: Making it Easier! 

Here’s the exciting part. Our new QEC release, QEC 2.0, makes using ECPs easier than ever before. You don’t have to be an expert in the scientific details to use this powerful technique. QEC 2.0 gives you access to ready-to-use ECPs that have been optimised and validated by Quantemol’s expert scientists, so you can focus on your research without getting bogged down in the technical complexities.

With QEC 2.0, a problem that was once a computational mountain becomes a much more manageable and streamlined task. It opens up new doors for studying heavy molecules and pushing the boundaries of your research in electron-molecule collisions.

Ready to see how QEC 2.0 can transform your own research? Contact us today to sign up for a trial. QEC 2.0 will be released on October 1st, 2025!

By Greg Armstrong & Annie Laver