No Imaginary frequency

[lxs234]

Hello everyone,

I am calculating the pre-factor of self-diffusion and solute in hcp Ti, I did the CI-NEB calculation to find the activation energy and then I calculate the frequencies at the saddle point using IBRION 5 and the CONTCAR obtained by the NEB calculations. I was expecting two real frequencies and one imaginary at saddle point, but for some jumps (for example the self-diffusion perpendicular to c-axes) I obtained three real frequencies. I am using 54-supercell
This is my INCAR for NEB calculation:


ENCUT = 350
EDIFF = 1E-6
EDIFFG = -0.01
ISMEAR = 1
SIGMA = 0.2
ISPIN=2
ISIF = 3
ICHAIN=0
IBRION = 1
POTIM = 0.5
IMAGES=1
SPRING=-5
LCLIMB=.TRUE.
LNEBCELL=.FALSE.
NSIM=1
NSW=200
NELM=20
IALGO=48

I am doing a first calcuation with
LREAL=Auto
and then I run with LREAL=.FALSE.

This is my guess POSCAR for the saddle point where the first atom is the one that moves

53Ti
2.926
2.9935452304690999 0.0000000000000000 0.0000000000000000
1.4967726152345500 2.5924862169507499 0.0000000000000000
0.0000000000000000 0.0000000000000000 4.7189209834061296
Ti
53
Direct
0.1697561818886160 0.9938578510281810 0.0000000000000000
0.1112266638061140 0.1109399470818570 0.1638141691539590
0.9999711711446440 0.0007233026837063 0.3298283599681580
0.1120999965868140 0.1092094280983280 0.5000000000000000
0.9999711711446440 0.0007233026837063 0.6701716400318420
0.1112266638061140 0.1109399470818570 0.8361858308460410
0.9991397651193170 0.3351338891894780 0.0000000000000000
0.1107290869969190 0.4437757160629760 0.1663876453343850
0.0006555906194379 0.3319849640573340 0.3332045293794260
0.1118780145233520 0.4448398096557080 0.5000000000000000
0.0006555906194379 0.3319849640573340 0.6667954706205740
0.1107290869969190 0.4437757160629760 0.8336123546656150
0.9969494739670030 0.6688179686300230 0.0000000000000000
0.1116086796156420 0.7785021216454880 0.1657423772837490
0.0006844194747941 0.6666361426395220 0.3327818839414820
0.1096537396495590 0.7791348868657590 0.5000000000000000
0.0006844194747941 0.6666361426395220 0.6672181160585180
0.1116086796156420 0.7785021216454880 0.8342576227162510
0.4448264644062940 0.1100603544631330 0.1644594372045950
0.3326794378856840 0.0006844194747941 0.3298009054348410
0.4428378642696840 0.1114337029721210 0.5000000000000000
0.3326794378856840 0.0006844194747941 0.6701990945651590
0.4448264644062940 0.1100603544631330 0.8355405627954050
0.3302417103945140 0.3342346651198440 0.0000000000000000
0.4439763456551060 0.4453948821438660 0.1651230870589300
0.3340566360170420 0.3326388595049860 0.3324427566239120
0.4450981595413810 0.4431530008779310 0.5000000000000000
0.3340566360170420 0.3326388595049860 0.6675572433760880
0.4439763456551060 0.4453948821438660 0.8348769129410700
0.3311409344641480 0.6710082597823370 0.0000000000000000
0.4431745646109700 0.7785560760564780 0.1656576248960530
0.3334027405693900 0.6666073137841660 0.3332045293794260
0.4445998144356270 0.7791453770262610 0.5000000000000000
0.3334027405693900 0.6666073137841660 0.6667954706205740
0.4431745646109700 0.7785560760564780 0.8343423751039470
0.6697193004165310 0.9938578510281810 0.0000000000000000
0.7784018068495731 0.1100898283306680 0.1644778190082940
0.6659416688111720 0.0014077221585005 0.3332045293794260
0.7790057119230730 0.1114697233700250 0.5000000000000000
0.6659416688111720 0.0014077221585005 0.6667954706205740
0.7784018068495731 0.1100898283306680 0.8355221809917061
0.6688179686300230 0.3342325574029700 0.0000000000000000
0.7788377770700911 0.4437429823485420 0.1663212747503880
0.6666361426395220 0.3326794378856840 0.3324387536352910
0.7765699451463211 0.4449149510438740 0.5000000000000000
0.6666361426395220 0.3326794378856840 0.6675612463647090
0.7788377770700911 0.4437429823485420 0.8336787252496120
0.6675679984531731 0.6688569578189780 0.0000000000000000
0.7772186109892020 0.7789380918660060 0.1675858330258430
0.6659721928383140 0.6666378378113080 0.3327068763675560
0.7782567539240970 0.7766991200890060 0.5000000000000000
0.6659721928383140 0.6666378378113080 0.6672931236324440
0.7772186109892020 0.7789380918660060 0.8324141669741570

After the NEB calculation I have obtained this CONTCAR

53Ti
2.92600000000000
2.9585678837268850 0.0000035621064222 0.0000000000000000
1.4792876198448097 2.6250050888181375 0.0000000000000000
0.0000000000000000 0.0000000000000000 4.7017825753109301
Ti
53
Direct
0.1867957432909293 0.9598219452959569 0.0000000000000000
0.1015125839282405 0.1303588154687461 0.1737926556621545
0.0014915983740451 0.9951371178002617 0.3303140864085137
0.1067322880573158 0.1198630329268013 0.5000000000000000
0.0014915983740451 0.9951371178002617 0.6696859135914863
0.1015125839282405 0.1303588154687461 0.8262073443378455
0.9941812297641377 0.3449175622654082 0.0000000000000000
0.1115984526690212 0.4564374744871671 0.1646279329072016
0.9950508028234282 0.3433020935798083 0.3335406327707204
0.1096343193656395 0.4503133506279227 0.5000000000000000
0.9950508028234282 0.3433020935798083 0.6664593672292796
0.1115984526690212 0.4564374744871671 0.8353720670927984
0.9906622347977816 0.6831572695921651 0.0000000000000000
0.1130842221253090 0.7874301159738621 0.1606770641753243
0.0043662250991545 0.6666700632228810 0.3330085131010421
0.1131788330861809 0.7804114787125513 0.5000000000000000
0.0043662250991545 0.6666700632228810 0.6669914868989579
0.1130842221253090 0.7874301159738621 0.8393229358246757
0.4370114211767842 0.1056725700282328 0.1588471253866715
0.3367901459174547 0.9951996501323208 0.3303197302667584
0.4447572970589420 0.1106820753664977 0.5000000000000000
0.3367901459174547 0.9951996501323208 0.6696802697332416
0.4370114211767842 0.1056725700282328 0.8411528746133214
0.3311118262225676 0.3238395962680514 0.0000000000000000
0.4515753099319255 0.4301650958728729 0.1692285117938397
0.3331072629911986 0.3237273950020878 0.3323534973940170
0.4438283752391570 0.4456485679586066 0.5000000000000000
0.3331072629911986 0.3237273950020878 0.6676465026059830
0.4515753099319255 0.4301650958728729 0.8307714882061603
0.3538054689696395 0.6257519632787449 0.0000000000000000
0.4326906128718946 0.7875056982968403 0.1606753872443107
0.3363150232975727 0.6607522218573294 0.3300141628517821
0.4396552051313662 0.7804702835012876 0.5000000000000000
0.3363150232975727 0.6607522218573294 0.6699858371482179
0.4326906128718946 0.7875056982968403 0.8393246127556822
0.6731669951873016 0.9869919810850902 0.0000000000000000
0.7905779420764958 0.1057587330097647 0.1588939991634319
0.6646973963115101 0.0039355300111978 0.3302620258683149
0.7780898686238942 0.1104626877278747 0.5000000000000000
0.6646973963115101 0.0039355300111978 0.6697379741316780
0.7905779420764958 0.1057587330097647 0.8411060008365681
0.6783979101928352 0.3237661636050149 0.0000000000000000
0.7651531406429228 0.4564357308450369 0.1646551088086383
0.6765785278534509 0.3236385455955926 0.3324256149171347
0.7735031618599848 0.4503939891545272 0.5000000000000000
0.6765785278534509 0.3236385455955926 0.6675743850828653
0.7651531406429228 0.4564357308450369 0.8353448911913617
0.6594943365649755 0.6830509849040709 0.0000000000000000
0.7765146838063330 0.7802651726487255 0.1694142797820248
0.6623041811146706 0.6666766151069510 0.3330062728867134
0.7755018950641528 0.7823197898470440 0.5000000000000000
0.6623041811146706 0.6666766151069510 0.6669937271132866
0.7765146838063330 0.7802651726487255 0.8305857202179752

As you can see after the relaxation the 1st atom is not any more at the saddle point
I tried to increase the Kpoint mesh but it gives me the same problem

Any suggestion?

Thank you

Lucia

[lxs234]

does anyone study diffusion in hcp-Ti and have the some problem?

thank you

Lucia