Dear Andrei, Thank you very much for your email.
What I mean by convergence study is: - I choose the accuracy for my energy calculations - Do several calculations with different values of meshcutoff energies - Plot the system energy (converged within the accuracy selected previously) - Select the value of meshcutoff from were the system energy is stable Is this ok? []'s, Camps On Mon, Dec 19, 2016 at 8:59 PM, Andrei Postnikov < andrei.postni...@univ-lorraine.fr> wrote: > A small comment to the latest remarks, > sorry as it must be obvious: > it hardly makes sense to run the convergence test on a calculation of just > one molecule > (or, in any standalone calculation) because you wont't have a clue > what exactly, and to which accuracy, should be converged. > Typically, you are after the energy difference between two (or more) cases: > atoms vs molecule, free molecule + surface vs adsorbed molecule, etc. > The convergence to be checked > is that of the meaningful energy difference, to the accuracy you need. > > Best regards > > Andrei Postnikov > > ----- I. Camps <ica...@gmail.com> a écrit : > > > Dear Riya, > > Its always good that, instead selecting those parameters (cutoff energy, > cell parameters, numbers of k points, etc.) manually, you run convergence > test. In this way, maybe you get smaller values for them and then less > computational resources involved. > > []'s, > > Camps > > > > > On Sat, Dec 17, 2016 at 8:23 PM, Riya Rogers <rogers.riy...@gmail.com> > wrote: > >> Dear Dr Camps >> >> > >> >> Thank u so much. I m taking very high cutoff greater than 340Ry. N put >> the Molecule in middle of big lattice. >> >> > My bond lengths are lil away frm exam abt 1.2 to 1.4%. >> >> > >> >> Thanking you >> >> > >> >> Regards >> >> > Riya >> >> > >> >> On 18-Dec-2016 2:40 am, "I. Camps" <ica...@gmail.com> wrote: >> >>> >>> >>>> > >>>> >>>> Can anyone tell me how to calculate energy of one molecule of gas. >>>> >>>> > >>>> >>>> Should I take molecule inside lattice? >>>> >>>> > Or >>>> >>>> > Should I follow the following example1: >>>> >>>> > >>>> >>>> http://personales.unican.es/junqueraj/JavierJunquera_ >>>> files/Metodos/Basic/Basic-exercises.html >>>> >>> >>> SIESTA is designed for periodic calculation, so, you have to put your >>> molecule inside a fictional lattice. The lattice vectors should be big >>> enough to not get interaction between two neighborhood molecules. Take a >>> look in the second example. Also, you can check how SIESTA is treating your >>> system (molecular, surface, slab, etc.) in the output file. >>> >>> >>>> > >>>> >>>> Does k points n meshcutoff and basis set info req? >>>> >>> Yes. >>> >>> >>> K vectors has meaning only for periodic system, so, in case of a >>> molecule, only one is needed (the gamma point (0,0,0). >>> >>> For the meshcutoff, you should do the convergence study as usually. >>> >>> The basis set should be selected according the accuracy you want or need >>> (as in any SIESTA calculation). >>> >>> Regards, >>> >>> -- >>> >>> []`s >>> >>> > >>> >>> Camps >>> >>> > >>> >>> > >> >> >> > >> >
