Re: [Wien] No convergence during Volume Optimization
Thank you Prof Laurence for your answer As I said in my answer to Dr Pieper I have resolved the problem by using another cell parameters and with other points. This problem happens usually when doing volume optimization and I my procedure to resolve the problem was to delete the points with convergence problem or choosing the cell parameters leading to energy close to the minmum energy with different points . Best regards -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] No convergence during Volume Optimization
Thank you Dr Pieper for the rich information. Yes I have a antiferromagnetic material and for the convergence problem ; the calculation jumps to the next point before reaching the energy criteria (foe example with energy criteria of 0.0001 , it jumps when reaching energy difference of 0.0008 ). I have resolved the problem by using another values for the cell parameters and with different points for volume optimization. Thank you again for the apreciated help Best regards -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] No convergence during Volume Optimization
The 'difference between energy and force approaches' is just that: a different approach to find the equilibrium positions in space for the atoms and their electrons within the structural model given by the .struct file. The equilibrium is the energy minimum in the parameter space under consideration. An energy minimum means that the derivatives with respect to (atom) positions - that is the forces - vanish. Knowing the derivatives (forces) helps, of course, a lot in finding the minimum - they point the way to the next (local) minimum. In the user guide you see: --User guide -- 5.3.1 Lattice parameters (Volume, c/a, lattice parameters) Package optimize The auxilliary program optimize (x optimize) generates from an existing case.struct (or case initial.struct, which is generated at the first call of optimize) a series of struct files with various volumes (or c/a ratios, or other modified parameters) (depending on your input): . . . After execution of this script you should have a series of scf-files with energies corresponding to the modified parameters, which should allow you to find the corresponding equillibrium parameters. For the volume optimization an analysis tool is available, other tools are under development). -- The minimum total energy defines the equilibrium. The derivatives with respect to lattice parameters are not easy to obtain during the scf cycle so for lattice parameters an 'energy approach' is used. For the internal parameters this is different. Persons as ingenious as Prof. Marks can calculate the derivatives with respect to internal parameters from the charge distribution at affordable computational cost during the scf. --User guide -- 5.3.2 Minimization of internal parameters (min lapw) Most of the more complicated structures have free internal structural parameters, which can either be taken from experiment or optimized using the calculated forces on the nuclei. Starting with WIEN2k 11.1 there are two possibilities to determine the equilibrium position of all individual atoms automatically (obeying the symmetry constraints of a certain space group). One can use either the shell script min lapw, together with the program mini, which will run a scf-cycle, update the positions using the calculated forces and restarts a new scf cycle. This continues until forces drop below a certain value; or use the normal scf-scripts run lapw -min where in case.inm the switch MSR1 will be modified to MSR1a such that the charge density and the positions are simultaneously opti- mized during the scf-cycle. -- The first option uses what you call the 'force approach': in equilibrium, no forces should push the atoms around. The second option indicates a mixed approach: The positions of the atoms (according to forces acting on them) and the ones of the electrons (to minimize the total energy) are BOTH adjusted in each step of the scf. As I said, there can be many reasons why your calculation did not reach convergence for some structural parameters. Did the scf stop without errors because the maximum number of iterations was reached? If yes, what was this number of iterations? Maybe your convergence criteria are too strong for the numerical precision you set by parameters like RKMAX or the k-mesh? Maybe the scf oscillates between several good solutions (is it a magnetic case?). Maybe your starting configuration and/or the model Hamiltonian is completely off or missing some ingredient and the poor scf wanders helpless around, lost in a multidimensional world ... Best regards, Martin Pieper --- Dr. Martin Pieper Karl-Franzens University Institute of Physics Universitätsplatz 5 A-8010 Graz Austria Tel.: +43-(0)316-380-8564 Am 13.11.2016 19:14, schrieb Abderrahmane Reggad: Thank you Dr Pieper for your interesting to my questions. I have optimized the atomic positions before doing calculation. Tha thing that I didn't understand is that the convergence is reached for some points but not for others. For the "optimization notes " , there is no mention on the difference betwwen the energy and force approaches. Best regards -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] No convergence during Volume Optimization
Thank you Dr Pieper for your interesting to my questions. I have optimized the atomic positions before doing calculation. Tha thing that I didn't understand is that the convergence is reached for some points but not for others. For the "optimization notes " , there is no mention on the difference betwwen the energy and force approaches. Best regards -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] No convergence during Volume Optimization
Look at the curve energy vs. volume and decide yourself wether its worth the while to increase the number of iterations (assuming that's the reason for the 'jump to the next point'). It also is a good idea to look for reasons why the convergence is slow (problem in the struct file? Bad position for some atom? Lattice constants very far from equilibrium? ... there are a lot of less trivial possibilities) Concerning your other question wether or not optimization with respect to energy or with respect to forces is the same I recommend reading the section on structure optimization in the user guide, and perhaps the 'Optimization Notes' of L. D. Marks that you will find on the Wien2k website. I am completely unable to improve on those. Best luck Martin Pieper --- Dr. Martin Pieper Karl-Franzens University Institute of Physics Universitätsplatz 5 A-8010 Graz Austria Tel.: +43-(0)316-380-8564 Am 12.11.2016 12:31, schrieb Abderrahmane Reggad: Dear Wien Users Sometimes , It happens that during volume optimization , the calculation doesn't converge to the chosen energy criteria and jumps to the next point . In this case, should we delete this point and choose another point or we could accept this calculation. For example , with energy criteria value of 0.0001 and with some points (we take 3 points as example)/ - 6 percent point: ETEST: .00083 - 0 percent point: ETEST: .00034 - 6 percent point ETEST: .00013 Best regards -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
[Wien] No convergence during Volume Optimization
Dear Wien Users Sometimes , It happens that during volume optimization , the calculation doesn't converge to the chosen energy criteria and jumps to the next point . In this case, should we delete this point and choose another point or we could accept this calculation. For example , with energy criteria value of 0.0001 and with some points (we take 3 points as example)/ - 6 percent point: ETEST: .00083 - 0 percent point: ETEST: .00034 - 6 percent point ETEST: .00013 Best regards -- Mr: A.Reggad Laboratoire de Génie Physique Université Ibn Khaldoun - Tiaret Algerie ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
