Dear Victor I see two levels at which your question can be answered. At a technical level, the pw.x code (the "engine" of neb.x) starts from scratch the scf cycle of every image. If all your images converge the first scf iteration to a non-magnetic state then a) they will propagate the non-magnetic state to the following neb steps and b) the transition state might really be non-magnetic. You can force a paramagnetic ground state (tot_magnetization =/ 0) to have a paramagnetic transition state. However, note that at a "quantum chemistry" level, if you are right then your system jumps somewhere between a 2S+1=1 to a 2S+1=3 state (and then revert to a 2S+1=1 state in the end? Sounds strange but not unheard of, e.g. the rotation of ethylene around the double bond), and this cannot be mapped along a single PES. You could calculate the fully diamagnetic and fully paramamagnetic paths (i.e., including initial and final configurations, by constraining the tot_magnetization value) and then see if the paramagnetic curve goes below the diamagnetic curve around the transition state. Be aware of the fact that if your transition state is intrinsically a multireference state (e.g., a diradical like twisted ethylene, which cannot be described by a single determinant), then DFT-based numbers could be poor numbers... HTH Giuseppe
On Monday, February 08, 2016 06:26:29 AM Vic Bermudez wrote: > Hello, > > I'm doing a NEB calculation for a reaction where I suspect that the > transition state might be paramagnetic. In the "engine_input" section I set > 'nspin=2', and I set a non-zero starting magnetization for one of the atom > types. In the first SCF cycle of the first NEB iteration the absolute > magnetization is initially non-zero and converges to a zero absolute > magnetization. The total magnetization remains zero at all times. This > applies to all 15 of the NEB images. > However, in successive NEB iterations the SCF starts right from the > beginning with zero absolute and total magnetizations and remains at zero > for both quantities right up to SCF convergence. > Here's my question. Given all this, am I really doing a spin-polarized > calculation, or is my calculation actually spin-restricted. If the latter, > what should I be doing to get a spin-unrestricted NEB run ? > > Thank you in advance for your help. > > This is the relevant part of the input. Here I'm restarting a calculation > that was spin-restricted and appeared to be getting somewhat close to NEB > convergence > > BEGIN > BEGIN_PATH_INPUT > &PATH > restart_mode='restart', > string_method='neb', > ds=1.D0, > opt_scheme='broyden', > nstep_path=4000, > num_of_images=15, > k_max=0.6D0, > k_min=0.1D0, > first_last_opt=.TRUE., > use_freezing=.TRUE., > CI_scheme='auto' > / > END_PATH_INPUT > > BEGIN_ENGINE_INPUT > &CONTROL > title='NEB Run', > ! restart_mode='from_scratch', > pseudo_dir='/lustre/cmf/scratch/b/bermudez/QE_PP/', > ! outdir='/lustre/cmf/scratch/b/bermudez/NEB-SO2_2/', > etot_conv_thr=1.0D-4, > forc_conv_thr=1.0D-3, > verbosity='default' > / > > &SYSTEM > ibrav=8, > a=14.5898, b=14.7815, c=35.00, > nat=138, > ntyp=4, > ecutwfc=40.0, > ecutrho=400.0, > nspin=2, > starting_magnetization(1)=0.0, > starting_magnetization(2)=0.0, > starting_magnetization(3)=0.0, > starting_magnetization(4)=0.3333, > london=.true., > occupations='smearing', > smearing='gaussian', > degauss=0.002, > nosym=.TRUE. > / > > &ELECTRONS > electron_maxstep=200, > conv_thr=3.0D-9, > mixing_beta=0.7D0, > mixing_ndim=8, > mixing_mode='local-TF' > / > > ATOMIC_SPECIES > Zr 91.22 Zr.pbe-spn-kjpaw_psl.0.2.3.UPF > O 15.9994 O.pbe-n-kjpaw_psl.0.1.UPF > H 1.0079 H.pbe-kjpaw_psl.0.1.UPF > S 32.06 S.pbe-n-kjpaw_psl.0.1.UPF > > > Victor M. Bermudez > E-mail: bermu...@alum.mit.edu > > > _______________________________________________ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum ******************************************************** - Article premier - Les hommes naissent et demeurent libres et égaux en droits. Les distinctions sociales ne peuvent être fondées que sur l'utilité commune - Article 2 - Le but de toute association politique est la conservation des droits naturels et imprescriptibles de l'homme. Ces droits sont la liberté, la propriété, la sûreté et la résistance à l'oppression. ******************************************************** Giuseppe Mattioli CNR - ISTITUTO DI STRUTTURA DELLA MATERIA v. Salaria Km 29,300 - C.P. 10 I 00015 - Monterotondo Stazione (RM), Italy Tel + 39 06 90672836 - Fax +39 06 90672316 E-mail: <giuseppe.matti...@ism.cnr.it> http://www.ism.cnr.it/english/staff/mattiolig ResearcherID: F-6308-2012 _______________________________________________ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
