Dear all<div> I was studying the charge changes of two-dimensional piezoelectric materials under electric fields, and found that when the boundary is set as a period, the charge is actually concentrated in the middle of the material, which is not understandable. But if you use aperiodic boundaries, the charge will accumulate towards both ends of the material, which is normal. I tried the electric field and the periodic electric field respectively, and as long as the boundary is periodic, the charge will gather in the middle, which is incomprehensible, and I want to know why. What I want to study is periodic materials, and this periodic boundary is unavoidable.</div><div> </div><div>&GLOBAL PROJECT 468-zhouqi-0.004d-xybianjie-2024 PRINT_LEVEL LOW RUN_TYPE MD &END GLOBAL &FORCE_EVAL METHOD Quickstep &SUBSYS &CELL ABC 38.9946780817 32.5196269485 20.000 PERIODIC XY #Direction of applied PBC (geometry aspect) &END CELL &TOPOLOGY COORD_FILE_FORMAT XYZ COORD_FILE_NAME 468.xyz &CENTER_COORDINATES #Centering the atoms in the box &END &END # &VELOCITY #You can set initial atomic velocities in this section # &END VELOCITY &END SUBSYS &DFT # WFN_RESTART_FILE_NAME 400-RESTART.wfn CHARGE 0 #Net charge MULTIPLICITY 1 #Spin multiplicity &EFIELD INTENSITY 0.004 POLARISATION -1.00000 0.00000 0.00000 &END &QS EPS_DEFAULT 1E-10 #This is default. Set all EPS_xxx to values such that the energy will be correct up to this value EXTRAPOLATION ASPC #Extrapolation for wavefunction during e.g. MD. ASPC is default, PS also be used EXTRAPOLATION_ORDER 3 #Order for PS or ASPC extrapolation. 3 is default METHOD xTB &xTB CHECK_ATOMIC_CHARGES F #xTB calculation often crashes without setting this to false &PARAMETER DISPERSION_PARAMETER_FILE dftd3.dat PARAM_FILE_NAME xTB_parameters &END PARAMETER &END xTB &END QS &POISSON PERIODIC XY #Direction(s) of PBC for calculating electrostatics PSOLVER ANALYTIC #The way to solve Poisson equation &END POISSON &SCF MAX_SCF 20 #Maximum number of steps of inner SCF EPS_SCF 1.0E-05 #Convergence threshold of density matrix of inner SCF # SCF_GUESS RESTART #Use wavefunction from WFN_RESTART_FILE_NAME file as initial guess &OT PRECONDITIONER FULL_SINGLE_INVERSE MINIMIZER DIIS #CG is worth to consider in difficult cases LINESEARCH 2PNT #1D line search algorithm for CG. 2PNT is default, 3PNT is better but more costly. GOLD is best but very expensive &END OT &OUTER_SCF MAX_SCF 20 #Maximum number of steps of outer SCF EPS_SCF 1.0E-05 #Convergence threshold of outer SCF &END OUTER_SCF &PRINT &RESTART OFF #Do not generate wfn file to suppress meaningless I/O cost &END RESTART &END PRINT &END SCF &END DFT &END FORCE_EVAL &MOTION &MD ENSEMBLE NVT STEPS 250000 #Number of steps to run TIMESTEP 1.0 #Step size in fs. Decrease it properly for high temperature simulation TEMPERATURE 5 #Initial and maintained temperature (K) &THERMOSTAT TYPE NOSE &END THERMOSTAT &END MD &CONSTRAINT &FIXED_ATOMS #Set atoms to be fixed COMPONENTS_TO_FIX XYZ #Which fractional components will be fixed, can be X, Y, Z, XY, XZ, YZ, XYZ LIST 357..468 &END FIXED_ATOMS &END CONSTRAINT &PRINT &TRAJECTORY &EACH MD 1 #Output frequency of coordinate &END EACH FORMAT xyz &END TRAJECTORY &RESTART BACKUP_COPIES 0 #Maximum number of backing up restart file, 0 means never &EACH MD 100 #Frequency of updating last restart file. Default is 20 &END EACH &END RESTART &RESTART_HISTORY &EACH MD 1000 #How many steps a history .restart file is generated. Default is 500 &END EACH &END RESTART_HISTORY &END PRINT &END MOTION </div><div> </div><div>Thanks</div><div>Evelyn Navarro</div> -- You received this message because you are subscribed to the Google Groups "cp2k" group. To unsubscribe from this group and stop receiving emails from it, send an email to <a href="mailto:cp2k+unsubscribe@googlegroups.com">cp2k+unsubscribe@googlegroups.com</a>. To view this discussion on the web visit <a href="https://groups.google.com/d/msgid/cp2k/0b163d78-c506-4817-97d6-ba7f187a4e85n%40googlegroups.com?utm_medium=email&utm_source=footer">https://groups.google.com/d/msgid/cp2k/0b163d78-c506-4817-97d6-ba7f187a4e85n%40googlegroups.com</a>.