I would introduce a penalty function such as A(N-C)**2, where C is the constraining coordination, and N the effective number of neighbors, calculated using your favorite definition. Not sure this has ever been implemented in QE, but it should not be a difficult task ... SB
On Jun 12, 2011, at 4:41 AM, m.g.p.krishna at chem.leidenuniv.nl wrote: > Dear List, > > In many situations, one need to constraint the .coordination. number > of atoms, so that, say, a chemically adsorbed molecule wont move away > from the reactant > surface (ie. to keep coordination number as a constant, bonds never > break w.r.t. a cutoff radius). > > In order to test that constraint optimization in Quantum Espresso > [4.3], I use an ethane molecule as test case. > > My doubt: > How can one constraint the .coordination number. of an atom (so that > the bonds of that particular atom, will remain the same before and > after the optimizatio > n, regardless of the ions displacements). > > Please note that in my test.in I used a shorter C-C bond length > (1.3Ang.) which is supposed to increase and it didn.t. I used > 'atom_coord' and 'type_coord' > and in all time it tried to keep the bond fixed! > > Can any one give an idea on how to fix the coordination number in a > geometry optimization? Hope some one can also explain why it always > fixes the bondlength > and not following the <0 0 0> and <0 0 1> flags? > > Please also see below for my test run, > > Thanks in advance, > > Krishna Mohan GP > Center for Superfunctional Materials > POSTECH > Sotuh Korea. > > > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > &CONTROL > calculation = 'relax' , > restart_mode = 'from_scratch' , > outdir = './' , > pseudo_dir = '/home01/a202kks/krishna/myPSP' , > prefix = 'Final_' , > verbosity = 'high' , > nstep = 50 , > tprnfor = .true., > / > &SYSTEM > ibrav = 0, > celldm(1)= 1., > nat = 8, > ntyp = 2, > ecutwfc = 20 , > nosym = .true. , > occupations = 'smearing', > smearing = 'gauss', > degauss = 0.002, > / > &ELECTRONS > / > &IONS > ion_dynamics='damp', > / > > CONSTRAINTS > 1 0.5 > 'atom_coord' 5 1 3.5 0.5 > > CELL_PARAMETERS Cubic > 12 0 0 > 0 12 0 > 0 0 12 > ATOMIC_SPECIES > C 12.0107 C.pbe-paw_kj.UPF > H 1.00674 H.pbe-paw_kj.UPF > K_POINTS automatic > 3 3 3 0 0 0 > ATOMIC_POSITIONS angstrom > C -0.00000000 -0.00000000 0.6500000 0 0 1 > H 0.00000000 1.00880567 1.0066666 0 0 0 > H 0.87365134 -0.50440284 1.0066666 0 0 0 > H -0.87365134 -0.50440284 1.0066666 0 0 0 > C -0.00000000 -0.00000000 -0.6500000 0 0 1 > H 0.87365134 0.50440284 -1.0066666 0 0 0 > H -0.87365134 0.50440284 -1.0066666 0 0 0 > H -0.00000000 -1.00880567 -1.0066666 0 0 0 > > ----------------------------------------------------------------------------- > After geometry optimization, I Got: > Damped Dynamics: convergence achieved in 11 steps > . . . . . . > Begin final coordinates > new unit-cell volume = 1728.00000 a.u.^3 ( 256.06318 Ang^3 ) > > CELL_PARAMETERS (alat= 1.00000000) > 12.000000000 0.000000000 0.000000000 > 0.000000000 12.000000000 0.000000000 > 0.000000000 0.000000000 12.000000000 > > ATOMIC_POSITIONS (angstrom) > C 0.000000000 -0.001564190 0.649998147 > H 0.000000000 1.058348951 1.147005976 > H 0.919069360 -0.531092625 1.145321656 > H -0.919069360 -0.531092625 1.145321656 > C 0.000000000 0.001564190 -0.649998147 > H 0.919069360 0.531092625 -1.145321656 > H -0.919069360 0.531092625 -1.145321656 > H 0.000000000 -1.058348951 -1.147005976 > End final coordinates > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum --- Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center - Trieste http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype) La morale est une logique de l'action comme la logique est une morale de la pens?e - Jean Piaget Please, if possible, don't send me MS Word or PowerPoint attachments Why? See: http://www.gnu.org/philosophy/no-word-attachments.html -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110614/fc771ca2/attachment-0001.htm
