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exercises:2019_conexs_newcastle:ex1 [2019/09/10 11:30] – [Part 1: Basic input] abussyexercises:2019_conexs_newcastle:ex1 [2020/08/21 10:15] (current) – external edit 127.0.0.1
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 The input file is structured in different sections, started by the "&SECTION_NAME" and ended by "&END SECTION NAME" where the including the section name after &END is optional but recommended. Each section may contain additional sections, and keywords used to control the parameters. There are three main input sections that we will use in this exercise: The input file is structured in different sections, started by the "&SECTION_NAME" and ended by "&END SECTION NAME" where the including the section name after &END is optional but recommended. Each section may contain additional sections, and keywords used to control the parameters. There are three main input sections that we will use in this exercise:
  
-    - "&GLOBAL" - which contains the general options such as the kind of run (in this case ENERGY) and the name of the project. +    - "&GLOBAL" - contains the general options such as the kind of run (in this case ENERGY) and the name of the project. 
-    - "&FORCE_EVAL" - which sets the parameters needed to evaluate the forces on the atoms, including the atomic positions, DFT functional, and basis set. +    - "&FORCE_EVAL" - sets the parameters needed to evaluate the forces on the atoms, including the atomic positions, DFT functional, and basis set. 
-    - "&MOTION" - which controls e.g. geometry optimizations and MD.+    - "&MOTION" - controls e.g. geometry optimizations and MD.
          
 The &GLOBAL section is quite straightforward and controls the type of calculation, our project’s name, etc. but the &FORCE_EVAL section is more complicated and we will go through the most important parts more carefully. The keyword  The &GLOBAL section is quite straightforward and controls the type of calculation, our project’s name, etc. but the &FORCE_EVAL section is more complicated and we will go through the most important parts more carefully. The keyword 
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 </code> </code>
 sets how much of the new density that should be mixed with the old density in each step. In this case, 60 % of the new density will be combined with 40 % of the old density when moving on to the next step. A small mixing parameter ALPHA will slow down the calculation but can help with convergence in hard cases. Finally the &MGRID section  sets how much of the new density that should be mixed with the old density in each step. In this case, 60 % of the new density will be combined with 40 % of the old density when moving on to the next step. A small mixing parameter ALPHA will slow down the calculation but can help with convergence in hard cases. Finally the &MGRID section 
 +<code>
 &MGRID &MGRID
   NGRIDS        4   NGRIDS        4
Line 98: Line 99:
   REL_CUTOFF    60   REL_CUTOFF    60
 &END &END
 +</code>
 controls how to set up the integration grid used in the Quickstep method. NGRIDS chooses the number of multigrids to use, CUTOFF selects the number of plane-wave basis functions to describe the electron density, and the REL_CUTOFF determines the grid spacing of the Gaussian basis functions. controls how to set up the integration grid used in the Quickstep method. NGRIDS chooses the number of multigrids to use, CUTOFF selects the number of plane-wave basis functions to describe the electron density, and the REL_CUTOFF determines the grid spacing of the Gaussian basis functions.
  
 After the &DFT section, the other main part of &FORCE_EVAL is the &SUBSYS. Here we set up the system we would like to study including basis sets and potentials. The &CELL and the &COORD sections After the &DFT section, the other main part of &FORCE_EVAL is the &SUBSYS. Here we set up the system we would like to study including basis sets and potentials. The &CELL and the &COORD sections
- +<code> 
-    &CELL +&CELL 
-      ABC 15.0 15.0 15.0 +  ABC 15.0 15.0 15.0 
-      ANGLES 90.00 90.00 90.00 +  ANGLES 90.00 90.00 90.00 
-    &END CELL +&END CELL 
-    &COORD +&COORD 
-      O  0 0 0 + O  0.0 0.0 0.0 
-      H  0.7 0.7 0 + H  0.7 0.7 0.0 
-      H -0.7 0.7 0 + H -0.7 0.7 0.0 
-    &END COORD  +&END COORD  
-sets up our simulation cell and atomic coordinates respectively. In the &KIND sections,  +</code> 
-    &KIND H                  +sets up our simulation cell and atomic coordinates respectively. By default, CP2K will run your calculations with periodic boundary conditions but since we are using a large simulation box, the molecule does not interact with its own copies and we are effectively looking at it in gas phase. In the &KIND sections,  
-      BASIS_SET DZVP-GTH +<code> 
-      POTENTIAL GTH-BLYP-q1 +&KIND H                  
-    &END KIND +  BASIS_SET DZVP-GTH 
-    &KIND O +  POTENTIAL GTH-BLYP-q1 
-      BASIS_SET DZVP-GTH +&END KIND 
-      POTENTIAL GTH-BLYP-q6 +&KIND O 
-    &END KIND+  BASIS_SET DZVP-GTH 
 +  POTENTIAL GTH-BLYP-q6 
 +&END KIND 
 +</code>
 the basis sets and potentials associated with each atom is given. In this case, we use GTH pseudopotentials and corresponding basis sets optimized for them. the basis sets and potentials associated with each atom is given. In this case, we use GTH pseudopotentials and corresponding basis sets optimized for them.
  
-Remember that a lot of information about the sections and the keywords can be found in the CP2K manual https://manual.cp2k.org/.    +Remember that a lot of information about the different sections and the keywords can be found in the CP2K manual https://manual.cp2k.org/.     
 + 
 +=====Part 2: Running an single-point calculation===== 
 + 
 +We are now ready to run the input in CP2K. To start the calculation, type 
 +<code> 
 +/cp2k.sopt -i water.inp -o water.out &  
 +</code> 
 +or  
 +<code> 
 +sbatch cp2k.sh 
 +</code> 
 +if you are logged in to the cluster and have modified the //cp2k.sh// accordingly. When the program is finished, you will have two new files in your working directory: 
 +<code> 
 +water.out    
 +h2o-RESTART.wfn 
 +</code> 
 +The first file ending with .out is the main output file of the calculation which contains information about the optimization 
 +<code> 
 +SCF PARAMETERS         Density guess:                                    ATOMIC 
 +                        -------------------------------------------------------- 
 +                        max_scf:                                             300 
 +                        max_scf_history:                                       0 
 +                        max_diis:                                              4 
 +                        -------------------------------------------------------- 
 +                        eps_scf:                                        1.00E-06 
 +                        eps_scf_history:                                0.00E+00 
 +                        eps_diis:                                       1.00E-01 
 +                        eps_eigval:                                     1.00E-05 
 +                        -------------------------------------------------------- 
 +                        level_shift [a.u.]:                                 0.00 
 +                        -------------------------------------------------------- 
 +                        Mixing method:                           DIRECT_P_MIXING 
 +                        -------------------------------------------------------- 
 +                        No outer SCF 
 + 
 + Number of electrons:                                                          8 
 + Number of occupied orbitals:                                                  4 
 + Number of molecular orbitals:                                                 4 
 + 
 + Number of orbital functions:                                                 23 
 + Number of independent orbital functions:                                     23 
 + 
 + Extrapolation method: initial_guess 
 + 
 + 
 + SCF WAVEFUNCTION OPTIMIZATION 
 + 
 +  Step     Update method      Time    Convergence         Total energy    Change 
 +  ------------------------------------------------------------------------------ 
 +     1 P_Mix/Diag. 0.60E+00    2.3     0.81098873       -17.0423550185 -1.70E+01 
 +     2 P_Mix/Diag. 0.60E+00    2.6     0.50875403       -17.1088252836 -6.65E-02 
 +     3 P_Mix/Diag. 0.60E+00    2.7     0.31846629       -17.1438061995 -3.50E-02 
 +     4 P_Mix/Diag. 0.60E+00    2.7     0.23820162       -17.1640209526 -2.02E-02 
 +     5 P_Mix/Diag. 0.60E+00    2.7     0.16669867       -17.1752275067 -1.12E-02 
 +     6 P_Mix/Diag. 0.60E+00    2.8     0.13086134       -17.1817453111 -6.52E-03 
 +     7 P_Mix/Diag. 0.60E+00    2.7     0.09423552       -17.1854419077 -3.70E-03 
 +     8 DIIS/Diag.  0.55E-01    2.7     0.02674149       -17.1876018813 -2.16E-03 
 +     9 DIIS/Diag.  0.12E-03    2.6     0.00054023       -17.1905995511 -3.00E-03 
 +    10 DIIS/Diag.  0.16E-03    2.7     0.00033668       -17.1905995449  6.19E-09 
 +    11 DIIS/Diag.  0.39E-05    2.7     0.00000741       -17.1905995597 -1.48E-08 
 +    12 DIIS/Diag.  0.12E-05    2.6     0.00000090       -17.1905995597 -1.00E-11 
 + 
 +  *** SCF run converged in    12 steps *** 
 +</code> 
 +as well as the converged results: 
 +<code> 
 +Electronic density on regular grids:         -7.9999999840        0.0000000160 
 +  Core density on regular grids:                7.9999999997       -0.0000000003 
 +  Total charge density on r-space grids:        0.0000000157 
 +  Total charge density g-space grids:           0.0000000157 
 + 
 +  Overlap energy of the core charge distribution:               0.00000001850899 
 +  Self energy of the core charge distribution:                -44.54061621428737 
 +  Core Hamiltonian energy:                                     12.90570300282121 
 +  Hartree energy:                                              18.65475043862882 
 +  Exchange-correlation energy:                                 -4.21043680541513 
 + 
 +  Total energy:                                               -17.19059955974348 
 + 
 + ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):              -17.190599559743479 
 +</code> 
 +The output file also contains information about timing, i.e. how much time was spent on the different parts in the code, and also ends with references to cite, relevant to your particular calculation. 
 + 
 +The second file contains the optimized Kohn-Sham wavefunction, which can be used to restart your calculation using the keyword 
 +<code> 
 +SCF_GUESS RESTART 
 +</code>     
 +in the &SCF section. 
 + 
 + 
 +=====Part 3: Geometry optimization===== 
 + 
 +In our previous calculation, our guess for the geometry of the water molecule, e.g. with a bond angle of 90°, was not very good. It is very often a good idea to optimize the geometry of your system before extracting any information from your calculations. Make another directory and move a copy of our previous input into it. To perform a geometry optimization, we must add an additional section to our input file. 
 +<code> 
 +&MOTION 
 +  &GEO_OPT 
 +    OPTIMIZER BFGS 
 +    MAX_DR    3.0E-03 
 +    MAX_FORCE 4.5E-04 
 +    RMS_DR    1.5E-03 
 +    RMS_FORCE 3.0E-04    
 +  &END 
 +  &CONSTRAINT 
 +    &FIXED_ATOMS 
 +      COMPONENTS_TO_FIX XYZ 
 +      LIST 1 
 +    &END 
 +  &END CONSTRAINT    
 +&END MOTION 
 +</code> 
 +In the &GEO_OPT section we select which kind of optimizer we want as well as the convergence criterion, such as the maximum force component. Then, since we only want to optimize the hydrogen relative to the oxygen, the &CONSTRAINT section allows us to freeze all components of the first atom in our input coordinates (make sure this is the oxygen by examining the &SUBSYS section again). Finally, we must also change the RUN_TYPE to GEO_OPT in the &GLOBAL section. 
 +<code> 
 +&GLOBAL 
 +  PROJECT h2o_opt 
 +  RUN_TYPE GEO_OPT 
 +  IOLEVEL LOW 
 +&END GLOBAL 
 +</code> 
 + 
 +We are now ready to start the calculation. As before, type e.g. 
 +<code> 
 +./cp2k.sopt -i water_opt.inp -o water_opt.out &  
 +</code> 
 +or  
 +<code> 
 +./cp2k.sopt water.inp | tee water.out 
 +</code>     
 +into your terminal to start the calculation. A geometry optimization contains more SCF cycles and so this calculation will take more time than before. Once the system has converged, we can examine the output file to evaluate our calculation. At each step in the optimization, we get the same information as in the last exercise, along with 
 +<code> 
 + --------  Informations at step =     2 ------------ 
 +  Optimization Method        =                 BFGS 
 +  Total Energy               =       -17.1947218061 
 +  Real energy change         =        -0.0002999093 
 +  Predicted change in energy =        -0.0002336556 
 +  Scaling factor             =         0.0000000000 
 +  Step size                  =         0.0178822087 
 +  Trust radius               =         0.4724315332 
 +  Decrease in energy         =                  YES 
 +  Used time                  =               22.246 
 + 
 +  Convergence check : 
 +  Max. step size             =         0.0178822087 
 +  Conv. limit for step size  =         0.0030000000 
 +  Convergence in step size   =                   NO 
 +  RMS step size              =         0.0091540732 
 +  Conv. limit for RMS step   =         0.0015000000 
 +  Convergence in RMS step    =                   NO 
 +  Max. gradient              =         0.0026713842 
 +  Conv. limit for gradients  =         0.0004500000 
 +  Conv. for gradients        =                   NO 
 +  RMS gradient               =         0.0017198827 
 +  Conv. limit for RMS grad.  =         0.0003000000 
 +  Conv. for gradients        =                   NO 
 + --------------------------------------------------- 
 +</code>  
 +describing each step. It is very important to check that your geometry optimization has converged properly, and this can be done by looking at the end of the output file. The last step should look something like this: 
 +<code> 
 + --------  Informations at step =     4 ------------ 
 +  Optimization Method        =                 BFGS 
 +  Total Energy               =       -17.1947556096 
 +  Real energy change         =        -0.0000002510 
 +  Predicted change in energy =        -0.0000002260 
 +  Scaling factor             =         0.0000000000 
 +  Step size                  =         0.0009840890 
 +  Trust radius               =         0.4724315332 
 +  Decrease in energy         =                  YES 
 +  Used time                  =               20.295 
 + 
 +  Convergence check : 
 +  Max. step size             =         0.0009840890 
 +  Conv. limit for step size  =         0.0030000000 
 +  Convergence in step size   =                  YES 
 +  RMS step size              =         0.0006410487 
 +  Conv. limit for RMS step   =         0.0015000000 
 +  Convergence in RMS step    =                  YES 
 +  Max. gradient              =         0.0000198391 
 +  Conv. limit for gradients  =         0.0004500000 
 +  Conv. in gradients         =                  YES 
 +  RMS gradient               =         0.0000096694 
 +  Conv. limit for RMS grad.  =         0.0003000000 
 +  Conv. in RMS gradients     =                  YES 
 + --------------------------------------------------- 
 + 
 + ******************************************************************************* 
 + ***                    GEOMETRY OPTIMIZATION COMPLETED                      *** 
 + ******************************************************************************* 
 +</code> 
 +Make sure that the calculation has converged by all criteria. You should also have several more files in your working directory, including e.g. 
 + 
 +    *h2o_opt-1.restart 
 +    *h2o_opt-1.restart.bak-1 
 +    *h2o_opt-pos-1.xyz 
 +     
 +The h2o_opt-1.restart contains all the input required to restart a calculation from the last step in the calculation. Its h2o_opt-1.restart.bak-1 analogue is the backup containing information from the previous step, and so on. The last file h2o_opt-pos-1.xyz contains the atomic trajectory of the optimization.  
 + 
 +Try to open it in e.g. Molden(?) to visualize the steps. 
 + 
 +Here we can see that the bond angle is now 102.8°, which is better but still quite far from the accepted 104.45°. Also comparing the final total energy to our first single-point calculation, we can see that our new geometry is more energetically stable. 
 + 
 +=====Part 4: Computing PDOS===== 
 + 
 +Now that we have obtained a more reasonable geometry, we will know attempt to compute the eigenvalues of our Kohn-Sham orbitals and compare the energy levels to the attached experimental spectra. We will also use this opportunity to try out the option to restart a calculation.  
 +-0.316280 
 +To restart our calculation from the previous geometry optimization, we need to copy two files from the old working directory, e.g. 
 +    h2o_opt-RESTART.wfn 
 +    h2o_opt-1.restart 
 +to our current working directory. To make the code read these files, we have to add a section 
 +<code> 
 +&EXT_RESTART 
 +  RESTART_FILE_NAME h2o_opt-1.restart 
 +&END EXT_RESTART 
 +</code>     
 +as well as adding  
 +<code> 
 +SCF_GUESS RESTART 
 +RESTART_FILE_NAME h2o_opt-RESTART.wfn 
 +</code>     
 +to the &SCF and &DFT sections respectively. To print the PDOS, we also need to add the &PDOS section under &DFT 
 +<code> 
 +&PRINT 
 +  &PDOS 
 +     FILENAME ./pdos 
 +     NLUMO 2 
 +  &END 
 +&END 
 +</code> 
 +and specify the spectra file names for example if we want to include unoccupied virtual orbitals. The final input can e.g. look like this: 
 +<code> 
 +&DFT 
 +  BASIS_SET_FILE_NAME GTH_BASIS_SETS 
 +  POTENTIAL_FILE_NAME GTH_POTENTIALS 
 +  LSD 0 
 +  RESTART_FILE_NAME h2o_opt-RESTART.wfn 
 +  &QS 
 +    METHOD GPW       
 +    EPS_DEFAULT 1.0E-10 
 +  &END QS 
 +  &SCF 
 +    MAX_SCF    300 
 +    EPS_SCF    1.0E-06 
 +    SCF_GUESS RESTART 
 +    &MIXING 
 +      METHOD DIRECT_P_MIXING 
 +      ALPHA   0.6 
 +    &END MIXING 
 +    &DIAGONALIZATION 
 +      ALGORITHM STANDARD 
 +    &END DIAGONALIZATION        
 +  &END SCF 
 +  &MGRID 
 +    NGRIDS 4 
 +    CUTOFF 300 
 +    REL_CUTOFF 60 
 +  &END 
 +  &XC 
 +    &XC_FUNCTIONAL BLYP 
 +    &END XC_FUNCTIONAL 
 +  &END XC   
 +  &PRINT 
 +    &PDOS 
 +      FILENAME ./h2o 
 +      NLUMO 2 
 +    &END 
 +  &END    
 +&END DFT 
 +</code> 
 +When the calculation is done, open the file 
 +    *h2o-k1-1.pdos    
 +and compare your calculated energies to the experimental measurements reported in the attached paper, e.g. Fig. 1. As a reminder, one 1 a.u. = 27.212 eV. Look in particular on the energy differences between the three valence states. 
 + 
 +{{:exercises:2019_conexs_newcastle:h2o_pes.pdf | Water PES}} 
 +---- 
 +=====Part 5: (Optional) Testing your parameters===== 
 + 
 +If you followed this exercise closely, chances are that the computed orbital energies in your PDOS files are quite similar to the experimental ones, given an ad hoc shift of the energies. However, the 1b2 orbital will be slightly off. Can we do better by tweaking our input, or can we get as good results with a faster method? In this exercise, we will investigate and try to get a feel for how different parameters affect the accuracy and time consumption of your calculation. Go back to Part 3 and Part 4 and redo the calculation while changing the following parameters  
 +<code> 
 +&XC_FUNCTIONAL  {PADE BLYP B3LYP} 
 + 
 +CUTOFF          {100 300 600} 
 + 
 +BASIS_SET       {SZV-GTH DZVP-GTH TZVP-GTH}
  
 +EPS_SCF         {1.0E-04 1.0E-06 1.0E-0.8}
 +</code>    
 +(choose one of the suggested in the brackets). The suggestions are given from less accurate to more accurate. When you feel comfortable, feel free to experiment with other keywords!   Note that using e.g. a larger basis set will make the calculation take longer, so you might want to do something else in the mean time.
  
  
exercises/2019_conexs_newcastle/ex1.1568115019.txt.gz · Last modified: 2020/08/21 10:15 (external edit)