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[link=hyperlink url]Dear All,
I've done some energy cutoff convergence test, but the resuts(Shown below) seems not so "Converged". Before 500eV, the energy increases except at 320 eV. But after 500eV, the energy change doesn't have any apparent trend. Shouldn't the energy increase as the ENCUT increases? The system has 120 atoms, Kpoint mesh is 3x1x1, I've also tried 7x3x3, the energy changes are similar to 3x1x1 case and doesn't converge on energy cutoff either. The structure for the test is optimized using 3x1x1. Any ideas or suggestions? Thanks a lot.

300 eV
1 F= -.74853017E+03 E0= -.74827186E+03 d E =-.516625E+00 mag= 51.0105
320
1 F= -.74910027E+03 E0= -.74883761E+03 d E =-.525320E+00 mag= 50.9958
350
1 F= -.74791619E+03 E0= -.74765148E+03 d E =-.529428E+00 mag= 50.9899
380
1 F= -.74787108E+03 E0= -.74760697E+03 d E =-.528223E+00 mag= 50.9842
420
1 F= -.74728692E+03 E0= -.74702348E+03 d E =-.526890E+00 mag= 50.9828
440
1 F= -.74686536E+03 E0= -.74660181E+03 d E =-.527093E+00 mag= 50.9817
450
1 F= -.74683427E+03 E0= -.74657087E+03 d E =-.526812E+00 mag= 50.9819
460
1 F= -.74677719E+03 E0= -.74651379E+03 d E =-.526801E+00 mag= 50.9849
480
1 F= -.74658979E+03 E0= -.74632637E+03 d E =-.526834E+00 mag= 50.9856
500
1 F= -.74643435E+03 E0= -.74617102E+03 d E =-.526651E+00 mag= 50.9858
600
1 F= -.74665073E+03 E0= -.74638749E+03 d E =-.526486E+00 mag= 50.9816
700
1 F= -.74679237E+03 E0= -.74652913E+03 d E =-.526478E+00 mag= 50.9814
800
1 F= -.74689104E+03 E0= -.74662774E+03 d E =-.526597E+00 mag= 50.9850
900
1 F= -.74688729E+03 E0= -.74662405E+03 d E =-.526480E+00 mag= 50.9824
1000
1 F= -.74690676E+03 E0= -.74664360E+03 d E =-.526327E+00 mag= 50.9823

It seems this sort of behavior is normal aince the energy could increase due to the kinetic energy error correction. What is the sufficient energy converge criterion for a 120 atom? 1meV/atom? 10meV/atom system? Or is there a criterion for kinetic energy error(shown below)? Thanks.

300 eV
kinetic energy error for atom= 0.0133 (will be added to EATOM!!)
kinetic energy error for atom= 1.2025 (will be added to EATOM!!)
kinetic energy error for atom= 0.0290 (will be added to EATOM!!)
kinetic energy error for atom= 0.0245 (will be added to EATOM!!)
kinetic energy error for atom= 1.1955 (will be added to EATOM!!)
320
kinetic energy error for atom= 0.0076 (will be added to EATOM!!)
kinetic energy error for atom= 0.6068 (will be added to EATOM!!)
kinetic energy error for atom= 0.0279 (will be added to EATOM!!)
kinetic energy error for atom= 0.0239 (will be added to EATOM!!)
kinetic energy error for atom= 0.7698 (will be added to EATOM!!)
340
kinetic energy error for atom= 0.0056 (will be added to EATOM!!)
kinetic energy error for atom= 0.3006 (will be added to EATOM!!)
kinetic energy error for atom= 0.0243 (will be added to EATOM!!)
kinetic energy error for atom= 0.0214 (will be added to EATOM!!)
kinetic energy error for atom= 0.4799 (will be added to EATOM!!)
350
kinetic energy error for atom= 0.0053 (will be added to EATOM!!)
kinetic energy error for atom= 0.2200 (will be added to EATOM!!)
kinetic energy error for atom= 0.0218 (will be added to EATOM!!)
kinetic energy error for atom= 0.0195 (will be added to EATOM!!)
kinetic energy error for atom= 0.3782 (will be added to EATOM!!)
360
kinetic energy error for atom= 0.0052 (will be added to EATOM!!)
kinetic energy error for atom= 0.1681 (will be added to EATOM!!)
kinetic energy error for atom= 0.0190 (will be added to EATOM!!)
kinetic energy error for atom= 0.0172 (will be added to EATOM!!)
kinetic energy error for atom= 0.2974 (will be added to EATOM!!)
380
kinetic energy error for atom= 0.0051 (will be added to EATOM!!)
kinetic energy error for atom= 0.1182 (will be added to EATOM!!)
kinetic energy error for atom= 0.0136 (will be added to EATOM!!)
kinetic energy error for atom= 0.0127 (will be added to EATOM!!)
kinetic energy error for atom= 0.1844 (will be added to EATOM!!)
420
kinetic energy error for atom= 0.0048 (will be added to EATOM!!)
kinetic energy error for atom= 0.0978 (will be added to EATOM!!)
kinetic energy error for atom= 0.0060 (will be added to EATOM!!)
kinetic energy error for atom= 0.0058 (will be added to EATOM!!)
kinetic energy error for atom= 0.0724 (will be added to EATOM!!)
440
kinetic energy error for atom= 0.0043 (will be added to EATOM!!)
kinetic energy error for atom= 0.0947 (will be added to EATOM!!)
kinetic energy error for atom= 0.0040 (will be added to EATOM!!)
kinetic energy error for atom= 0.0038 (will be added to EATOM!!)
kinetic energy error for atom= 0.0458 (will be added to EATOM!!)
450
kinetic energy error for atom= 0.0041 (will be added to EATOM!!)
kinetic energy error for atom= 0.0925 (will be added to EATOM!!)
kinetic energy error for atom= 0.0036 (will be added to EATOM!!)
kinetic energy error for atom= 0.0033 (will be added to EATOM!!)
kinetic energy error for atom= 0.0389 (will be added to EATOM!!)
460
kinetic energy error for atom= 0.0038 (will be added to EATOM!!)
kinetic energy error for atom= 0.0894 (will be added to EATOM!!)
kinetic energy error for atom= 0.0032 (will be added to EATOM!!)
kinetic energy error for atom= 0.0029 (will be added to EATOM!!)
kinetic energy error for atom= 0.0337 (will be added to EATOM!!)
480
kinetic energy error for atom= 0.0031 (will be added to EATOM!!)
kinetic energy error for atom= 0.0801 (will be added to EATOM!!)
kinetic energy error for atom= 0.0029 (will be added to EATOM!!)
kinetic energy error for atom= 0.0025 (will be added to EATOM!!)
kinetic energy error for atom= 0.0258 (will be added to EATOM!!)
500
kinetic energy error for atom= 0.0025 (will be added to EATOM!!)
kinetic energy error for atom= 0.0690 (will be added to EATOM!!)
kinetic energy error for atom= 0.0028 (will be added to EATOM!!)
kinetic energy error for atom= 0.0024 (will be added to EATOM!!)
kinetic energy error for atom= 0.0224 (will be added to EATOM!!)
600
kinetic energy error for atom= 0.0006 (will be added to EATOM!!)
kinetic energy error for atom= 0.0210 (will be added to EATOM!!)
kinetic energy error for atom= 0.0018 (will be added to EATOM!!)
kinetic energy error for atom= 0.0016 (will be added to EATOM!!)
kinetic energy error for atom= 0.0168 (will be added to EATOM!!)
700
kinetic energy error for atom= 0.0004 (will be added to EATOM!!)
kinetic energy error for atom= 0.0096 (will be added to EATOM!!)
kinetic energy error for atom= 0.0006 (will be added to EATOM!!)
kinetic energy error for atom= 0.0006 (will be added to EATOM!!)
kinetic energy error for atom= 0.0091 (will be added to EATOM!!)
800
kinetic energy error for atom= 0.0003 (will be added to EATOM!!)
kinetic energy error for atom= 0.0075 (will be added to EATOM!!)
kinetic energy error for atom= 0.0005 (will be added to EATOM!!)
kinetic energy error for atom= 0.0005 (will be added to EATOM!!)
kinetic energy error for atom= 0.0041 (will be added to EATOM!!)
900
kinetic energy error for atom= 0.0002 (will be added to EATOM!!)
kinetic energy error for atom= 0.0044 (will be added to EATOM!!)
kinetic energy error for atom= 0.0003 (will be added to EATOM!!)
kinetic energy error for atom= 0.0003 (will be added to EATOM!!)
kinetic energy error for atom= 0.0026 (will be added to EATOM!!)
1000
kinetic energy error for atom= 0.0001 (will be added to EATOM!!)
kinetic energy error for atom= 0.0025 (will be added to EATOM!!)
kinetic energy error for atom= 0.0002 (will be added to EATOM!!)
kinetic energy error for atom= 0.0001 (will be added to EATOM!!)
kinetic energy error for atom= 0.0022 (will be added to EATOM!!)








[quote="hyperlink url"]Dear All,
I've done some energy cutoff convergence test, but the resuts(Shown below) seems not so "Converged". Before 500eV, the energy increases except at 320 eV. But after 500eV, the energy change doesn't have any apparent trend. Shouldn't the energy increase as the ENCUT increases? The system has 120 atoms, Kpoint mesh is 3x1x1, I've also tried 7x3x3, the energy changes are similar to 3x1x1 case and doesn't converge on energy cutoff either. The structure for the test is optimized using 3x1x1. Any ideas or suggestions? Thanks a lot.

300 eV
1 F= -.74853017E+03 E0= -.74827186E+03 d E =-.516625E+00 mag= 51.0105
320
1 F= -.74910027E+03 E0= -.74883761E+03 d E =-.525320E+00 mag= 50.9958
350
1 F= -.74791619E+03 E0= -.74765148E+03 d E =-.529428E+00 mag= 50.9899
380
1 F= -.74787108E+03 E0= -.74760697E+03 d E =-.528223E+00 mag= 50.9842
420
1 F= -.74728692E+03 E0= -.74702348E+03 d E =-.526890E+00 mag= 50.9828
440
1 F= -.74686536E+03 E0= -.74660181E+03 d E =-.527093E+00 mag= 50.9817
450
1 F= -.74683427E+03 E0= -.74657087E+03 d E =-.526812E+00 mag= 50.9819
460
1 F= -.74677719E+03 E0= -.74651379E+03 d E =-.526801E+00 mag= 50.9849
480
1 F= -.74658979E+03 E0= -.74632637E+03 d E =-.526834E+00 mag= 50.9856
500
1 F= -.74643435E+03 E0= -.74617102E+03 d E =-.526651E+00 mag= 50.9858
600
1 F= -.74665073E+03 E0= -.74638749E+03 d E =-.526486E+00 mag= 50.9816
700
1 F= -.74679237E+03 E0= -.74652913E+03 d E =-.526478E+00 mag= 50.9814
800
1 F= -.74689104E+03 E0= -.74662774E+03 d E =-.526597E+00 mag= 50.9850
900
1 F= -.74688729E+03 E0= -.74662405E+03 d E =-.526480E+00 mag= 50.9824
1000
1 F= -.74690676E+03 E0= -.74664360E+03 d E =-.526327E+00 mag= 50.9823[/quote]</span>

Hi felixvasp,

since it's known that the total energy converges with higher cut-off energies, VASP adds an estimate to all atomic energies. If you substract this contributions, you'll find the expected convergency behaviour.

Cheers,

alex

Thanks for your reply, alex. I think after substract the added correction, the energy will converge on the encut. The problem is what is the typical energy criterion to find the good enough encut, say converged within 10meV/atom or 1meV/atom for a 120-atom system? or what is the typical kinetic energy error( small enough) for a 120-atom system?


quote=alex]Hi felixvasp,

since it's known that the total energy converges with higher cut-off energies, VASP adds an estimate to all atomic energies. If you substract this contributions, you'll find the expected convergency behaviour.

Cheers,

alex[/quote]</span>

Hi felixvasp,

I for myself am not on the quest for the overall convergence of a single calculation, but for the convergence of a property I'm interested in, e.g. an adsorption energy. This is mostly achieved at far lower cutoff energies compared to overall convergence.

Cheers,

alex