<div dir="ltr">Hi Matthias, I am using CP2k version 4.1. Here is an example input showing the problem: &GLOBAL PROJECT SnO2 RUN_TYPE CELL_OPT PRINT_LEVEL LOW &END GLOBAL &FORCE_EVAL METHOD QS STRESS_TENSOR ANALYTICAL &SUBSYS &CELL ABC 5.0 5.1 3.3 MULTIPLE_UNIT_CELL 3 3 4 &END CELL &TOPOLOGY COORD_FILE_FORMAT XYZ COORD_FILE_NAME ATOM_POSITIONS_INPUT MULTIPLE_UNIT_CELL 3 3 4 &END TOPOLOGY &KIND Sn BASIS_SET DZVP-MOLOPT-SR-GTH POTENTIAL GTH-PBE-q4 &END KIND &KIND O BASIS_SET DZVP-MOLOPT-SR-GTH POTENTIAL GTH-PBE-q6 &END KIND &END SUBSYS &DFT BASIS_SET_FILE_NAME BASIS_MOLOPT POTENTIAL_FILE_NAME GTH_POTENTIALS SPIN_POLARIZED T MULTIPLICITY 1 &QS EPS_DEFAULT 1.0E-8 METHOD GAPW &END QS &MGRID NGRIDS 5 CUTOFF 800 REL_CUTOFF 60 &END MGRID &SCF SCF_GUESS ATOMIC EPS_SCF 1.0E-06 MAX_SCF 1000 &OT ALGORITHM IRAC ENERGY_GAP 0.001 PRECONDITIONER FULL_ALL &END OT &END SCF &XC &XC_FUNCTIONAL PBE &END XC_FUNCTIONAL &END XC &END DFT &END FORCE_EVAL &MOTION &CELL_OPT TYPE GEO_OPT MAX_DR 1.0E-03 MAX_FORCE 1.0E-03 RMS_DR 1.0E-03 RMS_FORCE 1.0E-03 MAX_ITER 200 KEEP_ANGLES T OPTIMIZER BFGS &END CELL_OPT &GEO_OPT TYPE MINIMIZATION MAX_DR 1.0E-03 MAX_FORCE 1.0E-03 RMS_DR 1.0E-03 RMS_FORCE 1.0E-03 MAX_ITER 200 OPTIMIZER BFGS &END GEO_OPT &CONSTRAINT &FIXED_ATOMS COMPONENTS_TO_FIX XYZ LIST 1 &END FIXED_ATOMS &END CONSTRAINT &END MOTION This is the first part of the output, showing that the angles already change in the first step: ******************************************************************************* *** STARTING CELL OPTIMIZATION *** *** BFGS *** ******************************************************************************* CELL| Volume [angstrom^3]: 3029.400 CELL| Vector a [angstrom]: 15.000 0.000 0.000 |a| = 15.000 CELL| Vector b [angstrom]: 0.000 15.300 0.000 |b| = 15.300 CELL| Vector c [angstrom]: 0.000 0.000 13.200 |c| = 13.200 CELL| Angle (b,c), alpha [degree]: 90.000 CELL| Angle (a,c), beta [degree]: 90.000 CELL| Angle (a,b), gamma [degree]: 90.000 CELL| Numerically orthorhombic: YES -------- Informations at step = 0 ------------ Optimization Method = BFGS Total Energy = -2561.1655488258 Internal Pressure [bar] = -94313.1351913527 Used time = 4260.816 --------------------------------------------------- -------------------------- OPTIMIZATION STEP: 1 -------------------------- Step is scaled; Scaling factor = 0.58939 CELL| Volume [angstrom^3]: 2942.352 CELL| Vector a [angstrom]: 14.928 0.000 0.000 |a| = 14.928 CELL| Vector b [angstrom]: 0.000 15.220 0.000 |b| = 15.220 CELL| Vector c [angstrom]: 0.002 0.002 12.950 |c| = 12.950 CELL| Angle (b,c), alpha [degree]: 89.993 CELL| Angle (a,c), beta [degree]: 89.993 CELL| Angle (a,b), gamma [degree]: 90.000 CELL| Numerically orthorhombic: NO Best regards, Tobias </div>