Dear Chukwuemeka,
there are two possibilities: 1) if you are comparing the same stoichiometries, but different arrangements (e.g. 1 A atom, 1 B atom, 1 C atom, 1 D atom, or a multiple of these in a supercell) you just need to compare the energies out of PWscf for different arrangements; in each case, you want to calculate for the particular arrangement you chose the energy at relaxed atomic positions, and relaxed unit cell vectors. This would allow you to identify the best candidate among your trials (but of course you wouldn't know if there are better candidates, or if the system is thermodynamically stable with respect to decomposition in other, simpler compounds). 2) if you have a more complex case, where you are comparing compounds with different stoichiometries, you want to compare formation energies. For that, you could e.g. choose for each element its energy per atom at the ground-state structure of the elemental system (eg for Si, it would be the diamond lattice at equilibrium). So, for each of the 4 elements you need the energies of their elemental ground-state structure per atom (for Si, you divide by 2, since you have 2 atoms in the unit cell), and then you want to compare formation energies defined as E(A_i,B_j,C_k,D_l)-i*E(A)-j*E(B)-k*E(C)-l*E(D) where E(A_i,B_j,C_k,D_l) is the energy of your compound (at equilibrium) with an integer number i of atoms A, j atoms B, k atoms C, and l atoms D, and E(A) is the energy of the elemental compound for A at equilibrium, divided by the number of atoms that the elemental compound A as in the unit cell (same for E(B), ....). If the formation energy is negative, you would know that your system is stable, at 0K, with respect to decomposition in the end compounds - but you still wouldn't know if it is stable or not with respect to say decomposing into different binary compounds, or combinations of unaries, binaries, and ternaries. For more in-depth understanding, have a look at: http://oqmd.org/analysis/gclp/ nicola On 05/07/2017 23:59, Chukwuemeka Okoye wrote: > Dear All, > > I am using Quantum Espresso to perform calculations on quaternary > Heusler compounds. My question is, can I compare the total energies of > different types of atom arrangement in other to determine the most > stable configuration(correct ground state) between Type-I, Type-II and > Type-III? > Thanks. > > CMI Okoye > /------------------------------ > Chukwuemeka M I *Okoye* > / > /Department of Physics and Astronomy, > / > /University of Nigeria, > / > /Nsukka, Enugu State, > / > /Nigeria/ > Telephone: +234 7038766990 > E-mail: cmi.ok...@unn.edu.ng <mailto:cmi.ok...@unn.edu.ng> > > > _______________________________________________ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- ---------------------------------------------------------------------- Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL Director, National Centre for Competence in Research NCCR MARVEL, EPFL http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project _______________________________________________ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
