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I am a new user of Quantum Espresso. I have to use Deuterium instead of Hydrogen for my work in DFT studies. Hydrogen Pseudopotential file is available in QE website. Please clarify what parameters I have to set in the QE input file in order to simulate Deuterium in QE.

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  • $\begingroup$ Could you clarify what you mean and format your question? As written, it's tough to read and it's not obvious what you have already tried to resolve this issue. It looks like you have a pseudopotential for hydrogen and since deuterium is just an isotope, I would expect it's electronic properties to be largely the same. You may need to set other parameters in QE to do a calculation with deuterium. $\endgroup$
    – Tyberius
    Apr 1, 2022 at 13:07
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    $\begingroup$ @Tyberius I am not sure why this question is closed, you successfully answered it in a comment. The question probably doesn't need more details and this is a really common question for people to ask as they start investigating MD methods. We should reopen and you should answer more or less the same as your comment. PP is not affected by isotopes in practical applications, it's just a mass parameter. Maybe someone more physics heavy can answer if this is technically completely true though. $\endgroup$ Apr 1, 2022 at 15:50
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    $\begingroup$ @TristanMaxson it's really more an issue of the presentation of the post. My intent was to encourage them to format the post and to formulate an actual question beyond "give me this file". I'm fine with adding that as answer and reopening, but I want to encourage users (especially ones who have used the site for a while) to take some care with their posts rather than just a "do this for me, thanks" without further elaboration of what the actual problem is and how they have tried to address it. Closing a question early gives a user a chance to edit with out downvotes piling up. $\endgroup$
    – Tyberius
    Apr 1, 2022 at 15:54

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The main difference between deuterium and hydrogen is the mass, so you need to set the mass of the "hydrogen" so that it matches deuterium. I'm not a Quantum Espresso expert, but I think you do this by setting the ATOMIC_SPECIES card, see:

https://www.quantum-espresso.org/Doc/INPUT_PW.html#ATOMIC_SPECIES

However, you need to be clear about what effects you are wanting to simulate, because many common simulation tasks are not affected by the nuclear mass at all.

The pseudopotential doesn't care about the nuclear mass, so you don't need to change anything. For the same reason, the electronic ground state will be identical between hydrogen and deuterium, since Quantum Espresso uses an adiabatic approximation to decouple the nuclear and electronic wavefunctions. If you look at the "electronic" Kohn-Sham equations, the nuclear mass doesn't appear at all.

The optimised geometry of your material or molecule will also be the same; this is because Quantum Espresso optimises the structure at zero Kelvin and treats the atoms semi-classically, so there is no quantum delocalisation/zero-point motion for the nuclei - essentially, there is no nuclear kinetic energy term. If there is no temperature and no nuclear quantum effects, then the nuclear mass doesn't enter any of the equations and deuterium will give the same answer as hydrogen.

The mass will affect molecular dynamics and path-integral/ring-polymer molecular dynamics, and it will also affect any vibrational properties such as phonons (though the force constant matrix will be the same as for hydrogen). Other nuclear properties might be relevant for some kinds of simulations, such as the nuclear spin (e.g. for NMR chemical shifts).

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  • $\begingroup$ Thank You for the detailed information of isotopes in Quantum Espresso $\endgroup$
    – Nithyadevi
    Apr 8, 2022 at 1:35

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