<div dir="ltr">Dear Natalie for a non-periodic calculation, you have to specify "PERIODIC none" in the &CELL and in the &DFT section using for instance MT as the Poisson solver for the electrostatic decoupling: &POISSON PERIODIC none POISSON_SOLVER MT &END POISSON which is needed for the calculation of isolated systems. That won't solve, however, your convergence problem for the O atom. The DIIS method employed with diagonalisation is a very efficient for SCF convergence acceleration, but it is also very sensible to numerical noise. That issue can be fixed by increasing the CUTOFF, e.g. from 400 to 600 Ry. I have attached the output of such a run. You should also keep in mind that the convergence criterion applied for diagonalisation is different to the OT criterion. OT checks the energy convergence whereas the largest change in a density matrix element between two consecutive SCF steps is checked when using diagonalisation. Thus EPS_SCF can be 10-100 times larger with diagonalisation compared to OT. An EPS_SCF value of 1.0E-7 results in an energy convergence almost within machine precision as you can see in the attached output. Best regards Matthias On Thursday, 14 July 2016 04:05:20 UTC+2, Natalie Austin wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;"><div dir="ltr">Hello Matthias, The input file is below: &FORCE_EVAL METHOD QS &DFT BASIS_SET_FILE_NAME BASIS_MOLOPT POTENTIAL_FILE_NAME GTH_POTENTIALS &MGRID CUTOFF 400 REL_CUTOFF 60 NGRIDS 4 &END MGRID &QS EPS_DEFAULT 1.0E-14 MAP_CONSISTENT &END QS &SCF SCF_GUESS ATOMIC EPS_SCF 1.0E-7 MAX_SCF 500 CHOLESKY INVERSE &DIAGONALIZATION ALGORITHM STANDARD &END DIAGONALIZATION &MIXING METHOD DIRECT_P_MIXING ALPHA 0.1 # I also ran a case where I increased the value to 0.4 as you suggested. BETA 1.5 NBROYDEN 8 &END MIXING &END SCF &XC &XC_FUNCTIONAL PBE &PBE PARAMETRIZATION REVPBE &END PBE &END XC_FUNCTIONAL &VDW_POTENTIAL DISPERSION_FUNCTIONAL PAIR_POTENTIAL &PAIR_POTENTIAL TYPE DFTD3 REFERENCE_FUNCTIONAL PBE CALCULATE_C9_TERM .TRUE. PARAMETER_FILE_NAME dftd3.dat R_CUTOFF 15.0 VERBOSE_OUTPUT .TRUE. &END PAIR_POTENTIAL &END vdw_POTENTIAL &END XC MULTIPLICITY 3 UKS .TRUE. &END DFT &SUBSYS &CELL ABC 20.00000 20.00000 20.00000 ALPHA_BETA_GAMMA 90.00 90.00 90.00 PERIODIC NONE &END CELL &TOPOLOGY COORD_FILE_NAME <a href="http://o.xyz" target="_blank" rel="nofollow" onmousedown="this.href='http://www.google.com/url?q\x3dhttp%3A%2F%2Fo.xyz\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNHrT67bJhjeY_Jp_D3ZbyQAk-1paQ';return true;" onclick="this.href='http://www.google.com/url?q\x3dhttp%3A%2F%2Fo.xyz\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNHrT67bJhjeY_Jp_D3ZbyQAk-1paQ';return true;">o.xyz</a> COORDINATE XYZ &END TOPOLOGY &KIND O ELEMENT O BASIS_SET DZVP-MOLOPT-SR-GTH-q6 POTENTIAL GTH-PBE-q6 &END KIND &END SUBSYS &END FORCE_EVAL &GLOBAL PROJECT o RUN_TYPE ENERGY PRINT_LEVEL MEDIUM &END GLOBAL &MOTION &GEO_OPT MAX_FORCE 0.0004 MAX_ITER 2000 OPTIMIZER BFGS TYPE MINIMIZATION &END GEO_OPT &END MOTION and the coordinate file: 1 o O 7.46880 7.39185 7.47705 Natalie </div></blockquote></div>