I just ran the tetragonal structure under the orthorhombic symmetry. Now, the energy vs. strain curve is indeed smooth without a jump. Thank you. Before with the tetragonal symmetry (e=0), -0.25 -4018.092634 -0.1 -4018.09269 0 -4018.091181 0.1 -4018.09269 0.25 -4018.092634
After calculating the tetragonal under orthorhombic, -0.25 -4018.092634 -0.1 -4018.09269 0 -4018.092715 0.1 -4018.09269 0.25 -4018.092634 From: Wien <wien-boun...@zeus.theochem.tuwien.ac.at> on behalf of Park, Ken <kenneth_p...@baylor.edu> Date: Monday, November 14, 2022 at 8:19 AM To: A Mailing list for WIEN2k users <wien@zeus.theochem.tuwien.ac.at> Subject: Re: [Wien] ,IRelast: incorrect structure for e=0.3 in C44 for TiO2 Prof. Blaha, I apologize for not noticing the exceeded size limit of the email. Thank you for your comments, especially on calculating the low-symmetry structure in high symmetry. Sincerely, Ken From: Wien <wien-boun...@zeus.theochem.tuwien.ac.at> on behalf of Peter Blaha <peter.bl...@tuwien.ac.at> Date: Monday, November 14, 2022 at 3:29 AM To: A Mailing list for WIEN2k users <wien@zeus.theochem.tuwien.ac.at> Subject: [Wien] ,IRelast: incorrect structure for e=0.3 in C44 for TiO2 Your email must be smaller than 40 kB !!!! A couple of comments: Very small distortions are always problematic. When do you consider a certain symmetry fulfilled ? Due to the limited digits of certain numbers rounding problems (or factors like sqrt(2), or cos(45), ... may cause such rounding problems, which later on cause problems. I'm not surprised to see energy-jumps when comparing energies from a tetragonal case with an orthorhombic one, where the lattice vectors have been rotated. Such calculations would require "fully converged" meshes (k-mesh, FFT mesh,..). You should do the "high-symmetry" case also in the low-symmetry structure. For this, you have to initialize a low-symmetry distorted structure and AFTER init_lapw, change manually the lattice parameters such that you obtain the high-symmetry case. Do NOT rerun init_lapw afterwards. In essence: when symmetry (or better: the bravais lattice) changes, you should either not include the e=0 case in the analysis or run the e=0 case as I indicated above. PS: With a struct file, maybe the developer of IRestast could play around .... Best regards Peter Blaha --------------------- Von: "Park, Ken" <kenneth_p...@baylor.edu> Datum: 13.11.2022, 16:18 An: "wien@zeus.theochem.tuwien.ac.at" <wien@zeus.theochem.tuwien.ac.at> Dear Wien2k developers and experts, I have been using wien2k 21.1 and IRelast package to calculate the elastic constants for rutile TiO2 at pressure =0. When I used a small strain such as e = 0.3% was used for C44 (monoclinic distortion), the script generated an incorrect structure causing a crash. Below is a top portion of the structure with beta not equal to 90, for which wien2k expects alpha=beta=90. [parkk@login001 tio2r]$ head -10 tio2r.struct TiO2 CXZ LATTICE,NONEQUIV.ATOMS: 4 12 C2/m MODE OF CALC=RELA unit=bohr 12.390517 13.568280 12.390517 90.000000 90.000562155.460807 ATOM 1: X=0.00000000 Y=0.00000000 Z=0.00000000 MULT= 1 ISPLIT= 0 Ti1 NPT= 781 R0=0.00005000 RMT= 1.78000 Z: 22.0 LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000 0.0000000 1.0000000 0.0000000 0.0000000 0.0000000 1.0000000 The structures with e >= 0.5 seem working all right. Could you look into this issue? I also have been getting negative values of C44 and C66 in higher order fit (4). So, initially I thought I needed higher rkmax in calculating those elastic moduli, but then, I found out that the energy at e=0 remains higher compared to those up to about e < 1, despite of using rkmax up to 10. (See the attached figure for C66.) With more data points, it becomes clear that it is due to the e=0 data point lying above the neighboring points by about 1.5 mRy. I believe that different symmetry constraints are responsible for the energy discrepancy between e=0 (tetragonal) and e != 0 (orthorhombic ) as the distortion for C66 lowers the symmetry from the tetragonal to the orthorhombic. This would explain why I see a similar energy jump at e=0 also for C44, which involves the deformation from tetragonal to monoclinic whereas the other three distortions c11+c12, c33, and czz (all tetragonal) don’t show such. So, I think that in the calculation of the elastic moduli with the distortions involving symmetry change, the e=0 structure should not be included. Could you comment on this? If it may be convenient for you, I will be more than happy to provide you the structure and outputeos files. Respectfully, Ken Park -- -------------------------------------------------------------------------- Peter BLAHA, Inst.f. 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