CUTOFF收敛测试结果不稳定

aipacino

各位老师，我想考察磷酸水体系的质子状态，选好泛函和基组后测试CUTOFF，发现能量呈现阶梯式下降，这种情况应该如何确定CUTOFF的值？以下是我的输入文件
#Generated by Multiwfn (http://sobereva.com/multiwfn)
&GLOBAL
  PROJECT guess
  PRINT_LEVEL MEDIUM
  RUN_TYPE ENERGY_FORCE
&END GLOBAL

&FORCE_EVAL
  METHOD Quickstep
  &SUBSYS
    &CELL
      A    13.51000000     0.00000000     0.00000000
      B     0.00000000    13.51000000     0.00000000
      C     0.00000000     0.00000000    13.51000000
      PERIODIC XYZ #Direction(s) of applied PBC (geometry aspect)
    &END CELL
    &TOPOLOGY
      COORD_FILE_NAME mix.xyz      
      COORD_FILE_FORMAT XYZ     
    &END TOPOLOGY
    &KIND O
      ELEMENT O
      BASIS_SET TZV2P-MOLOPT-GTH-q6
      BASIS_SET AUX_FIT admm-tzp-q6
      POTENTIAL GTH-PBE0-q6
    &END KIND
    &KIND H
      ELEMENT H
      BASIS_SET TZV2P-MOLOPT-GTH-q1
      BASIS_SET AUX_FIT admm-tzp-q1
      POTENTIAL GTH-PBE0-q1
    &END KIND
    &KIND P
      ELEMENT P
      BASIS_SET TZV2P-MOLOPT-GTH-q5
      BASIS_SET AUX_FIT admm-tzp-q5
      POTENTIAL GTH-PBE0-q5
    &END KIND
  &END SUBSYS

  &DFT
    BASIS_SET_FILE_NAME  BASIS_MOLOPT
    BASIS_SET_FILE_NAME  BASIS_MOLOPT_UCL
    BASIS_SET_FILE_NAME  BASIS_ADMM_UZH
    POTENTIAL_FILE_NAME  POTENTIAL_UZH
    WFN_RESTART_FILE_NAME guess-RESTART.wfn
    CHARGE    1 #Net charge
    MULTIPLICITY    1 #Spin multiplicity
    &QS
      EPS_DEFAULT 1.0E-12 #Set all EPS_xxx to values such that the energy will be correct up to this value
      EPS_PGF_ORB 1E-15 #If warning "Kohn Sham matrix not 100% occupied" occurs and meantime calculation is unstable, decrease it
    &END QS
    &POISSON
      PERIODIC XYZ #Direction(s) of PBC for calculating electrostatics
      PSOLVER PERIODIC #The way to solve Poisson equation
    &END POISSON
    &XC
      &XC_FUNCTIONAL
        &PBE
          PARAMETRIZATION REVPBE
          SCALE_X 0.75
          SCALE_C 1.0
        &END PBE
      &END XC_FUNCTIONAL
      &XC_GRID
        XC_DERIV SPLINE2
      &END XC_GRID
      &HF
        FRACTION 0.25
        &SCREENING
          EPS_SCHWARZ 1.0E-8
          SCREEN_ON_INITIAL_P T
        &END SCREENING
        &MEMORY
          MAX_MEMORY 4000
          EPS_STORAGE_SCALING 0.1
        &END MEMORY
        &INTERACTION_POTENTIAL
          POTENTIAL_TYPE TRUNCATED
          CUTOFF_RADIUS 6
          T_C_G_DATA ./t_c_g.dat
        &END
        &HF_INFO
        &END HF_INFO
      &END
      &VDW_POTENTIAL
        POTENTIAL_TYPE PAIR_POTENTIAL
        &PAIR_POTENTIAL
          PARAMETER_FILE_NAME dftd3.dat
          TYPE DFTD3(BJ)
          R_CUTOFF 15
          LONG_RANGE_CORRECTION TRUE
          REFERENCE_FUNCTIONAL revPBE0
          #CALCULATE_C9_TERM T #Calculate C9-related three-body term, more accurate for large system
        &END PAIR_POTENTIAL
      &END VDW_POTENTIAL
    &END XC
    &AUXILIARY_DENSITY_MATRIX_METHOD
      METHOD BASIS_PROJECTION
      ADMM_PURIFICATION_METHOD MO_DIAG
    &END AUXILIARY_DENSITY_MATRIX_METHOD
    &MGRID
      CUTOFF  1000
      REL_CUTOFF  80
      NGRIDS 5
    &END MGRID
    &SCF
      MAX_SCF 128
      EPS_SCF 3.0E-08 #Convergence threshold of density matrix of inner SCF
      SCF_GUESS RESTART #Use wavefunction from WFN_RESTART_FILE_NAME file as initial guess
#     IGNORE_CONVERGENCE_FAILURE #Continue calculation even if SCF not converged, works for version >= 2024.1
      &OT
        PRECONDITIONER FULL_ALL #Usually best but expensive for large system. Cheaper: FULL_SINGLE_INVERSE and FULL_KINETIC
        MINIMIZER DIIS #CG is worth to consider in difficult cases
        LINESEARCH 2PNT #1D line search algorithm for CG. 2PNT is default. 3PNT is more expensive but may be better. GOLD is best but very expensive
        ALGORITHM STRICT #Algorithm of OT. Can be STRICT (default) or IRAC
      &END OT
      &PRINT
        &RESTART #Note: Use "&RESTART OFF" can prevent generating .wfn file
          BACKUP_COPIES 0 #Maximum number of backup copies of wfn file. 0 means never
        &END RESTART
      &END PRINT
    &END SCF
  &END DFT
  &PRINT
    &FORCES ON #Print atomic forces
    &END FORCES
  &END PRINT
&END FORCE_EVAL