force convergence : difficult to acheive for Y2Ti2O7
Posted: Sat Nov 29, 2008 12:32 pm
Hi, I am doing some calculations on Y2Ti2O7 for defect related properties. For that its necessary for me to study different defects configuration e.g. antisite defects, frenkel pairs, charged defects and their combinations.
I have reached necessary force convergence ( EDIFFG = -0.001) for perfect lattice structure. But for defect structure, I am not getting the force convergence at all ( forces on each atom not becoming lower than ~ 0.08 eV on few atoms).
I have tried various combinations of K point mesh, ENCUT, POTIM , IBRION , Prec=High and ISIF values, but it seems to be toooo difficult to achieve the force convergence. I am using PAW_PBE pseudopotentials as supplied with VASP ( Y_sv, Ti_sv and O) and EDIFF = 1.E-06. I am doing non-spin polarised calculation.
I am posting my INCAR and POSCAR file. Can anyone please suggest what parameters I need to tune to get the required force convergence .
********************
INCAR
********************
System = Y2Ti2O7
ISMEAR = 0 ! 1: Methfessel-Paxton order N; -1:Fermi-smearing.
SIGMA = 0.1 ! Smearing factor (in ev)
PREC = High ! sets cutoff and FFT grid
ENCUT = 550 ! planewave energy cutoff (in ev)[default taken from POTCAR file]
!ENAUG = 550 ! grep EAUG POTCAR
EDIFF = 1E-06 ! energy stoping criterion for electronic iteration
EDIFFG = -1E-2 ! energy stoping criterion for ionic Relaxation
ICHARG = 2 ! start from scratch(this flag determines how to construct the
! initial charge density. 0:calculate charge density from
! initial wave functions; 1:read the charge density from file
! CHGCAR and extrapolate from the old positions to new positions.
! in PAW and LDA+U method be careful (see manual); 2:take
! super-positions of atomic charges; 4: read potential file from
! POT file; +10: non self-consisitent calculation,it means that
!charge density will be kept constant during whole electronic
!minimization.
INIWAV = 1 ! 0:take "jellium wave functions"; 1: fill wave functions arrays
! with random nos (safest full-proof switch).
ISTART = 0 ! start from scratch.Initialize the wave functions according to
! the flag INIWAV
NELM = 100 ! maximum of 100 electronic steps.
!NELMIN = 5 ! minimum of 5 steps in each electronic SC
NELMDL = -20 !no update of charge for 12 steps.
LREAL = Auto !( making the calculation fast)
!ALGO = Fast ! (making the calculation fast)
IALGO = 48
NSIM = 4 ! (making the calculation fast);blocked algorithm update;4 bands
! at a time
!ISPIN = 2 ! 1:non-spin polarized calculations; 2:spin-polarized calculation
!MAGMOM = 16*1.5 16*1.5 56*1.5 ! (default: NIONS*1;for spin-pol cal a save default:expt mag mom
! *1.2 or 1.5)
!RWIGS = 1.3
LORBIT = 12
LWAVE = .FALSE. ! Print WAVCAR if .TRUE.
LCHARG = .FALSE. ! Print CHGCAR if .TRUE.
LVTOT = .FALSE.
ADDGRID = .TRUE. ! Set .TRUE. for PAW
LMAXMIX = 6
AMIX = 0.2
BMIX = 0.0001
AMIX_MAG = 0.8
BMIX_MAG = 0.0001
Ionic relaxation
NSW = 200 ! # of steps in optimization (default 0!)
ISIF = 2 ! 0: relax ions, 1,2:relax ions,calc stresses, 3:relax ion+cell
IBRION = 1 ! 1: quasi-NR, 2:CG algorithm for ions
NFREE = 10 ! number of DIIS vectors to save
POTIM = 0.5 ! reduce trial step in optimization
#Parallel Options
LPLANE = .TRUE.
LSCALU = .FALSE.
NPAR = 10 ! how many bands in parallel
NSIM = 4
*****************
POSCAR
*****************
Ti Y Ti Y Ti O
1.00000000000000
10.0954843460679555 0.0000000000000000 0.0000000000000000
0.0000000000000000 10.0954843460679555 0.0000000000000000
0.0000000000000000 0.0000000000000000 10.0954843460679555
1 15 9 1 6 56
Direct
0.5000000000000000 0.5000000000000000 0.5000000000000000
0.5000000000000000 0.0000000000000000 0.0000000000000000
0.0000000000000000 0.5000000000000000 0.0000000000000000
0.0000000000000000 0.0000000000000000 0.5000000000000000
0.2500000000000000 0.7500000000000000 0.0000000000000000
0.2500000000000000 0.2500000000000000 0.5000000000000000
0.7500000000000000 0.0000000000000000 0.2500000000000000
0.7500000000000000 0.5000000000000000 0.7500000000000000
0.0000000000000000 0.2500000000000000 0.7500000000000000
0.5000000000000000 0.2500000000000000 0.2500000000000000
0.2500000000000000 0.5000000000000000 0.2500000000000000
0.7500000000000000 0.2500000000000000 0.0000000000000000
0.7500000000000000 0.7500000000000000 0.5000000000000000
0.2500000000000000 0.0000000000000000 0.7500000000000000
0.0000000000000000 0.7500000000000000 0.2500000000000000
0.5000000000000000 0.7500000000000000 0.7500000000000000
0.0000000000000000 0.0000000000000000 0.0000000000000000
0.0000000000000000 0.5000000000000000 0.5000000000000000
0.5000000000000000 0.0000000000000000 0.5000000000000000
0.5000000000000000 0.5000000000000000 0.0000000000000000
0.7500000000000000 0.2500000000000000 0.5000000000000000
0.7500000000000000 0.7500000000000000 0.0000000000000000
0.2500000000000000 0.5000000000000000 0.7500000000000000
0.2500000000000000 0.0000000000000000 0.2500000000000000
0.7500000000000000 0.0000000000000000 0.7500000000000000
0.5000000000000000 0.7500000000000000 0.2500000000000000
0.0000000000000000 0.7500000000000000 0.7500000000000000
0.2500000000000000 0.7500000000000000 0.5000000000000000
0.2500000000000000 0.2500000000000000 0.0000000000000000
0.7500000000000000 0.5000000000000000 0.2500000000000000
0.5000000000000000 0.2500000000000000 0.7500000000000000
0.0000000000000000 0.2500000000000000 0.2500000000000000
0.3750000000000000 0.3750000000000000 0.3750000000000000
0.3750000000000000 0.8750000000000000 0.8750000000000000
0.8750000000000000 0.8750000000000000 0.3750000000000000
0.8750000000000000 0.3750000000000000 0.8750000000000000
0.1250000000000000 0.6250000000000000 0.1250000000000000
0.6250000000000000 0.6250000000000000 0.6250000000000000
0.6250000000000000 0.1250000000000000 0.1250000000000000
0.1250000000000000 0.1250000000000000 0.6250000000000000
0.3302091347961338 0.1250000000000000 0.1250000000000000
0.3302091347961338 0.6250000000000000 0.6250000000000000
0.8302091347961338 0.1250000000000000 0.6250000000000000
0.8302091347961338 0.6250000000000000 0.1250000000000000
0.4197908652038662 0.1250000000000000 0.6250000000000000
0.9197908652038662 0.6250000000000000 0.6250000000000000
0.9197908652038662 0.1250000000000000 0.1250000000000000
0.1250000000000000 0.3302091347961338 0.1250000000000000
0.1250000000000000 0.8302091347961338 0.6250000000000000
0.6250000000000000 0.8302091347961338 0.1250000000000000
0.6250000000000000 0.4197908652038662 0.1250000000000000
0.6250000000000000 0.9197908652038662 0.6250000000000000
0.6250000000000000 0.3302091347961338 0.6250000000000000
0.1250000000000000 0.1250000000000000 0.3302091347961338
0.1250000000000000 0.6250000000000000 0.8302091347961338
0.6250000000000000 0.1250000000000000 0.8302091347961338
0.1250000000000000 0.6250000000000000 0.4197908652038662
0.1250000000000000 0.1250000000000000 0.9197908652038662
0.6250000000000000 0.6250000000000000 0.9197908652038662
0.6250000000000000 0.6250000000000000 0.3302091347961338
0.8750000000000000 0.5802091347961338 0.3750000000000000
0.8750000000000000 0.0802091347961338 0.8750000000000000
0.8750000000000000 0.6697908652038662 0.8750000000000000
0.3750000000000000 0.1697908652038662 0.8750000000000000
0.3750000000000000 0.6697908652038662 0.3750000000000000
0.3750000000000000 0.0802091347961338 0.3750000000000000
0.0802091347961338 0.3750000000000000 0.3750000000000000
0.0802091347961338 0.8750000000000000 0.8750000000000000
0.1697908652038662 0.8750000000000000 0.3750000000000000
0.6697908652038662 0.8750000000000000 0.8750000000000000
0.6697908652038662 0.3750000000000000 0.3750000000000000
0.5802091347961338 0.3750000000000000 0.8750000000000000
0.8750000000000000 0.3750000000000000 0.1697908652038662
0.3750000000000000 0.3750000000000000 0.0802091347961338
0.8750000000000000 0.8750000000000000 0.0802091347961338
0.3750000000000000 0.8750000000000000 0.5802091347961338
0.8750000000000000 0.8750000000000000 0.6697908652038662
0.5802091347961338 0.8750000000000000 0.3750000000000000
0.1697908652038662 0.3750000000000000 0.8750000000000000
0.3750000000000000 0.5802091347961338 0.8750000000000000
0.8750000000000000 0.1697908652038662 0.3750000000000000
0.8750000000000000 0.3750000000000000 0.5802091347961338
0.3750000000000000 0.8750000000000000 0.1697908652038662
0.3750000000000000 0.3750000000000000 0.6697908652038662
0.1250000000000000 0.4197908652038662 0.6250000000000000
0.1250000000000000 0.9197908652038662 0.1250000000000000
0.4197908652038662 0.6250000000000000 0.1250000000000000
0.6250000000000000 0.1250000000000000 0.4197908652038662
I have reached necessary force convergence ( EDIFFG = -0.001) for perfect lattice structure. But for defect structure, I am not getting the force convergence at all ( forces on each atom not becoming lower than ~ 0.08 eV on few atoms).
I have tried various combinations of K point mesh, ENCUT, POTIM , IBRION , Prec=High and ISIF values, but it seems to be toooo difficult to achieve the force convergence. I am using PAW_PBE pseudopotentials as supplied with VASP ( Y_sv, Ti_sv and O) and EDIFF = 1.E-06. I am doing non-spin polarised calculation.
I am posting my INCAR and POSCAR file. Can anyone please suggest what parameters I need to tune to get the required force convergence .
********************
INCAR
********************
System = Y2Ti2O7
ISMEAR = 0 ! 1: Methfessel-Paxton order N; -1:Fermi-smearing.
SIGMA = 0.1 ! Smearing factor (in ev)
PREC = High ! sets cutoff and FFT grid
ENCUT = 550 ! planewave energy cutoff (in ev)[default taken from POTCAR file]
!ENAUG = 550 ! grep EAUG POTCAR
EDIFF = 1E-06 ! energy stoping criterion for electronic iteration
EDIFFG = -1E-2 ! energy stoping criterion for ionic Relaxation
ICHARG = 2 ! start from scratch(this flag determines how to construct the
! initial charge density. 0:calculate charge density from
! initial wave functions; 1:read the charge density from file
! CHGCAR and extrapolate from the old positions to new positions.
! in PAW and LDA+U method be careful (see manual); 2:take
! super-positions of atomic charges; 4: read potential file from
! POT file; +10: non self-consisitent calculation,it means that
!charge density will be kept constant during whole electronic
!minimization.
INIWAV = 1 ! 0:take "jellium wave functions"; 1: fill wave functions arrays
! with random nos (safest full-proof switch).
ISTART = 0 ! start from scratch.Initialize the wave functions according to
! the flag INIWAV
NELM = 100 ! maximum of 100 electronic steps.
!NELMIN = 5 ! minimum of 5 steps in each electronic SC
NELMDL = -20 !no update of charge for 12 steps.
LREAL = Auto !( making the calculation fast)
!ALGO = Fast ! (making the calculation fast)
IALGO = 48
NSIM = 4 ! (making the calculation fast);blocked algorithm update;4 bands
! at a time
!ISPIN = 2 ! 1:non-spin polarized calculations; 2:spin-polarized calculation
!MAGMOM = 16*1.5 16*1.5 56*1.5 ! (default: NIONS*1;for spin-pol cal a save default:expt mag mom
! *1.2 or 1.5)
!RWIGS = 1.3
LORBIT = 12
LWAVE = .FALSE. ! Print WAVCAR if .TRUE.
LCHARG = .FALSE. ! Print CHGCAR if .TRUE.
LVTOT = .FALSE.
ADDGRID = .TRUE. ! Set .TRUE. for PAW
LMAXMIX = 6
AMIX = 0.2
BMIX = 0.0001
AMIX_MAG = 0.8
BMIX_MAG = 0.0001
Ionic relaxation
NSW = 200 ! # of steps in optimization (default 0!)
ISIF = 2 ! 0: relax ions, 1,2:relax ions,calc stresses, 3:relax ion+cell
IBRION = 1 ! 1: quasi-NR, 2:CG algorithm for ions
NFREE = 10 ! number of DIIS vectors to save
POTIM = 0.5 ! reduce trial step in optimization
#Parallel Options
LPLANE = .TRUE.
LSCALU = .FALSE.
NPAR = 10 ! how many bands in parallel
NSIM = 4
*****************
POSCAR
*****************
Ti Y Ti Y Ti O
1.00000000000000
10.0954843460679555 0.0000000000000000 0.0000000000000000
0.0000000000000000 10.0954843460679555 0.0000000000000000
0.0000000000000000 0.0000000000000000 10.0954843460679555
1 15 9 1 6 56
Direct
0.5000000000000000 0.5000000000000000 0.5000000000000000
0.5000000000000000 0.0000000000000000 0.0000000000000000
0.0000000000000000 0.5000000000000000 0.0000000000000000
0.0000000000000000 0.0000000000000000 0.5000000000000000
0.2500000000000000 0.7500000000000000 0.0000000000000000
0.2500000000000000 0.2500000000000000 0.5000000000000000
0.7500000000000000 0.0000000000000000 0.2500000000000000
0.7500000000000000 0.5000000000000000 0.7500000000000000
0.0000000000000000 0.2500000000000000 0.7500000000000000
0.5000000000000000 0.2500000000000000 0.2500000000000000
0.2500000000000000 0.5000000000000000 0.2500000000000000
0.7500000000000000 0.2500000000000000 0.0000000000000000
0.7500000000000000 0.7500000000000000 0.5000000000000000
0.2500000000000000 0.0000000000000000 0.7500000000000000
0.0000000000000000 0.7500000000000000 0.2500000000000000
0.5000000000000000 0.7500000000000000 0.7500000000000000
0.0000000000000000 0.0000000000000000 0.0000000000000000
0.0000000000000000 0.5000000000000000 0.5000000000000000
0.5000000000000000 0.0000000000000000 0.5000000000000000
0.5000000000000000 0.5000000000000000 0.0000000000000000
0.7500000000000000 0.2500000000000000 0.5000000000000000
0.7500000000000000 0.7500000000000000 0.0000000000000000
0.2500000000000000 0.5000000000000000 0.7500000000000000
0.2500000000000000 0.0000000000000000 0.2500000000000000
0.7500000000000000 0.0000000000000000 0.7500000000000000
0.5000000000000000 0.7500000000000000 0.2500000000000000
0.0000000000000000 0.7500000000000000 0.7500000000000000
0.2500000000000000 0.7500000000000000 0.5000000000000000
0.2500000000000000 0.2500000000000000 0.0000000000000000
0.7500000000000000 0.5000000000000000 0.2500000000000000
0.5000000000000000 0.2500000000000000 0.7500000000000000
0.0000000000000000 0.2500000000000000 0.2500000000000000
0.3750000000000000 0.3750000000000000 0.3750000000000000
0.3750000000000000 0.8750000000000000 0.8750000000000000
0.8750000000000000 0.8750000000000000 0.3750000000000000
0.8750000000000000 0.3750000000000000 0.8750000000000000
0.1250000000000000 0.6250000000000000 0.1250000000000000
0.6250000000000000 0.6250000000000000 0.6250000000000000
0.6250000000000000 0.1250000000000000 0.1250000000000000
0.1250000000000000 0.1250000000000000 0.6250000000000000
0.3302091347961338 0.1250000000000000 0.1250000000000000
0.3302091347961338 0.6250000000000000 0.6250000000000000
0.8302091347961338 0.1250000000000000 0.6250000000000000
0.8302091347961338 0.6250000000000000 0.1250000000000000
0.4197908652038662 0.1250000000000000 0.6250000000000000
0.9197908652038662 0.6250000000000000 0.6250000000000000
0.9197908652038662 0.1250000000000000 0.1250000000000000
0.1250000000000000 0.3302091347961338 0.1250000000000000
0.1250000000000000 0.8302091347961338 0.6250000000000000
0.6250000000000000 0.8302091347961338 0.1250000000000000
0.6250000000000000 0.4197908652038662 0.1250000000000000
0.6250000000000000 0.9197908652038662 0.6250000000000000
0.6250000000000000 0.3302091347961338 0.6250000000000000
0.1250000000000000 0.1250000000000000 0.3302091347961338
0.1250000000000000 0.6250000000000000 0.8302091347961338
0.6250000000000000 0.1250000000000000 0.8302091347961338
0.1250000000000000 0.6250000000000000 0.4197908652038662
0.1250000000000000 0.1250000000000000 0.9197908652038662
0.6250000000000000 0.6250000000000000 0.9197908652038662
0.6250000000000000 0.6250000000000000 0.3302091347961338
0.8750000000000000 0.5802091347961338 0.3750000000000000
0.8750000000000000 0.0802091347961338 0.8750000000000000
0.8750000000000000 0.6697908652038662 0.8750000000000000
0.3750000000000000 0.1697908652038662 0.8750000000000000
0.3750000000000000 0.6697908652038662 0.3750000000000000
0.3750000000000000 0.0802091347961338 0.3750000000000000
0.0802091347961338 0.3750000000000000 0.3750000000000000
0.0802091347961338 0.8750000000000000 0.8750000000000000
0.1697908652038662 0.8750000000000000 0.3750000000000000
0.6697908652038662 0.8750000000000000 0.8750000000000000
0.6697908652038662 0.3750000000000000 0.3750000000000000
0.5802091347961338 0.3750000000000000 0.8750000000000000
0.8750000000000000 0.3750000000000000 0.1697908652038662
0.3750000000000000 0.3750000000000000 0.0802091347961338
0.8750000000000000 0.8750000000000000 0.0802091347961338
0.3750000000000000 0.8750000000000000 0.5802091347961338
0.8750000000000000 0.8750000000000000 0.6697908652038662
0.5802091347961338 0.8750000000000000 0.3750000000000000
0.1697908652038662 0.3750000000000000 0.8750000000000000
0.3750000000000000 0.5802091347961338 0.8750000000000000
0.8750000000000000 0.1697908652038662 0.3750000000000000
0.8750000000000000 0.3750000000000000 0.5802091347961338
0.3750000000000000 0.8750000000000000 0.1697908652038662
0.3750000000000000 0.3750000000000000 0.6697908652038662
0.1250000000000000 0.4197908652038662 0.6250000000000000
0.1250000000000000 0.9197908652038662 0.1250000000000000
0.4197908652038662 0.6250000000000000 0.1250000000000000
0.6250000000000000 0.1250000000000000 0.4197908652038662