Hi everyone.

I am currently trying to make use of ABINIT in my research, but I am incurring in some difficulties on how to use it, especially given that I lack a strong chemical background.

I understand the time that it would require to help me clarify these concepts. I will ask them in increasing order of complexity. Even understanding the simplest one would be very helpful to me. Thank you all in advance for your help.

**Computing Formation Energy**

I would like to compute the formation energy of some structures but I have some doubts regarding the procedure. From my understanding, given a structure with composition S = AnBm, the formation energy should be Ef(S) = E(S) - nE(A) - mE(B) (and similarly for compositions with more species). My question is: *how do I compute the energy of single, isolated elements?*

I followed the Base1 tutorial until the end, when it is explained how to compute the formation energy for H2. The main difficulty that I am facing is that, in that tutorial, in order to compute the total energy of H, some parameters need to be manually tuned (nsppol, nsym, *etc. etc.*) How can I tune them for arbitrary elements? Is there a general procedure or a reference list that I can use?

**Replicating results of OQMD**

For the most part, I am trying to replicate the results obtained by the Open Quantum Materials Database by referring to their DFT settings on a different simulator, VASP.

The problem is that for many parameters I can’t seem to find the analogous for ABINIT. For example: number of k-points per reciprocal atom (KPPRA), initial magnetic moments, or different approaches to pseudopotentials.

*Is there a way I can replicate their results in ABINIT? In the case not all parameters are transferrable, would the discrepancy between running ABINIT simulations and their results be too large?*

In order to answer that second question I could simply compute the results and compare, however I first need to understand how to compute the formation energy reliably, hence the first question.

Thank you everyone for your help. I recognize that I am probably asking for a lot, but I would be really grateful even for some slight hints and suggestions, not necessarily the full answers.