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I have been studying liquid systems (particularly deep eutectic solvents) using classical molecular dynamics (MD) simulations. The main drawback of classical MD is the arbitrariness of the potential parameters and hence it doesn't give accurate results for different experiments. I am planning to pursue ab initio MD simulations for such kind of systems, but I have no experience in any kind of ab initio methods.

Can you guys suggest tools (preferably free to use academic software) to start with such ab initio MD simulation for liquid systems?

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    $\begingroup$ CP2K is a great free software package for ab initio molecular dynamics. However, it has a bit of a steep learning curve due to less than ideal documentation! $\endgroup$
    – Hayden S
    Dec 11, 2022 at 18:26
  • $\begingroup$ @HaydenS do you think you can expand that into an answer like this one which provides some advantages (e.g. free) and disadvantages (e.g. steep learning curve, less-than-ideal documentation)? This would be far more valuable to the site and community than a temporary comment which can't be recovered once deleted (apart from diamond moderators and SE employees). $\endgroup$
    – Nike Dattani
    Dec 11, 2022 at 19:48
  • $\begingroup$ For eutectic solvents, you will want a fair amount of molecules and a large sample time. This means you will be likely be using a poor quality theory/basis set for ab-initio. I doubt it will be useful. You would probably have better luck with polarizable force-field or ReaxFF. Or, use a classical force-field wisely. What property are you trying to sample? Sampling wisely and using Thermodynamics to do the grunt work, can get very accurate results, despite what nay-sayers say for classical forcefields $\endgroup$
    – B. Kelly
    Dec 11, 2022 at 21:14
  • $\begingroup$ May I know what is ReaxFF? I am trying to simulate complex formations due to hydrogen bond formations. $\endgroup$
    – user35952
    Dec 12, 2022 at 8:11
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    $\begingroup$ "ReaxFF (for “reactive force field”) is a bond order-based force field developed by Adri van Duin, William A. Goddard, III, and co-workers at the California Institute of Technology. ... Whereas traditional force fields are unable to model chemical reactions because of the requirement of breaking and forming bonds (a force field's functional form depends on having all bonds defined explicitly), ReaxFF eschews explicit bonds in favor of bond orders, which allows for continuous bond formation/breaking." (link) $\endgroup$
    – Camps ♦
    Dec 12, 2022 at 11:54

1 Answer 1

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CP2K

CP2K is an open source electronic structure and molecular dynamics software package to perform atomistic simulations of solid-state, liquid, molecular, and biological systems. It is especially aimed at massively parallel and linear-scaling electronic structure methods and state-of-the-art ab initio molecular dynamics simulations. Excellent performance for electronic structure calculations is achieved using novel algorithms implemented for modern high-performance computing systems. This review revisits the main capabilities of CP2K to perform efficient and accurate electronic structure simulations. The emphasis is put on density functional theory and multiple post–Hartree–Fock methods using the Gaussian and plane wave approach and its augmented all-electron extension.

I recommend reading through their latest paper for an overview of CP2K's design, including strengths and weaknesses. One thing to note is that, unlike VASP, CP2K's DFT module (QuickStep) uses Gaussian + Augmented plane wave basis sets, rather than simply plane waves. This has both advantages and disadvantages; while it makes the code run efficiently, it introduces the problem of choosing an appropriate Gaussian basis set for your application. Sometimes the ideal Gaussian basis set just doesn't exist for your system of interest!

I have used CP2K in my research, and my experience is that while the software is extremely powerful and efficient, the documentation is lacking for many of the advanced or highly-specialized features. Even some of the more basic features sometimes have very terse descriptions in the documentation. However, you can usually find complete explanations in the scientific literature, and the documentation problem seems to be getting better over time.

An installation Guide can be found here. To start out, I recommend going through the exercises given here. Once you get going, you'll be referring often to the reference manual.

Thankfully, when it comes to the molecular dynamics of the situation, ab initio MD as implemented in CP2K (Born-Oppenheimer MD) works essentially the same as classical MD. The difference is really just in the force field, which is calculated on-the-fly via density functional theory methods.

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