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exercises:2016_ethz_mmm:basis_sets [2016/02/03 09:54]
exercises:2016_ethz_mmm:basis_sets [2020/08/21 10:15] (current)
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 +
 +====== Basis Sets ======
 +In this exercise you will compare different basis sets and use them for computing the binding energy of an H$_2$ molecule.
 +
 +The cp2k basis set format is described in detail [[:basis_sets|here]].
 +
 +===== Part I: Different basis sets for H and H$_2$ =====
 +==== 1.Step ====
 +
 +Run a calculation with the following input file. Comment lines are marked with !
 +
 +<code - mybasis.inp > 
 +&GLOBAL
 +  PROJECT H-mybasis
 +  RUN_TYPE ENERGY
 +&END GLOBAL
 +
 +&FORCE_EVAL
 +  METHOD Quickstep                         ! Electronic structure method (DFT,...)
 +  
 +  &DFT
 +  LSD                                      ! Requests a spin-polarized calculation for non paired electrons
 +  MULTIPLICITY 2                           ! Multiplicity = 2S+1 (S= total spin momentum)
 +    &POISSON                               ! Solver requested for non periodic calculations  
 +      PERIODIC NONE                        
 +      PSOLVER  WAVELET                     ! Type of solver
 +    &END POISSON
 +    &QS                                    ! Parameters needed to set up the Quickstep framework
 +      METHOD GAPW                          ! Method: gaussian and augmented plane waves 
 +    &END QS
 +    &XC                                    ! Parameters needed to compute the electronic exchange potential 
 +      &XC_FUNCTIONAL NONE                  ! No xc_functional
 +      &END XC_FUNCTIONAL
 +      &HF                                  ! Hartree Fock exchange. In this case is 100% (no fraction specified).                    
 +        &SCREENING                         ! Screening of the electronic repulsion up to the given threshold. This section is needed
 +          EPS_SCHWARZ 1.0E-10              ! Threshold specification
 +        &END SCREENING
 +      &END HF 
 +    &END XC
 +  &END DFT
 +  
 +  &SUBSYS
 +    &TOPOLOGY                              ! Section used to center the molecule in the simulation box. Useful for big molecules 
 +      &CENTER_COORDINATES                  
 +      &END
 +    &END
 +    &CELL
 +      ABC 10.0 10.0 10.0
 +      PERIODIC NONE                        ! Non periodic calculations. That's why the POISSON section is needed 
 +    &END CELL
 +    &COORD
 +       0.0 0.0 0.0                           
 +    &END COORD
 +    &KIND H
 +     &BASIS                                ! Basis set for H
 +     2
 +     1 0 0 1 1
 +     0.35 1
 +     1 0 0 1 1
 +     0.6 1
 +     &END
 +     POTENTIAL ALL                         ! Species that the potential is for all electron calculations.
 +     &POTENTIAL                            ! Usual all electron potential for H 
 +        0    0
 +     0.20000000    0
 +     &END POTENTIAL
 +    &END KIND
 +  &END SUBSYS
 +&END FORCE_EVAL
 +
 +</code>
 +
 +==== 2.Step ====
 +Try to change the basis set, and report the obtained energy values for H.
 +After a couple of tries on your own, try to use some of the literature basis sets (given at the end of this exercise).
 +At the end, you should get a table like this :
 +
 +
 +^ Basis set                     ^ Energy  H ($E_h$)      ^      
 +| mybasis (from given input)    | ....                   |
 +| basis try 1                   | ....                   
 +| basis try 2                   | ....                   |
 +| ....                          | ....                   |
 +| pc-0                          | ....                   
 +| pc-1                          | ....                   |
 +| pc-2                          | ....                   
 +
 +<note tip>Is always good to keep record of self-created basis sets, to track the effect of a change in value and number of exponents, contractions....etc.. </note>
 +
 +==== 3.Step ====
 +Repeat the procedure for H$_2$. For this you will have to add a second H atom to the coordinate section and run a **geometry optimization** to determine the equilibrium distance. Howto run a geometry optimization was covered in a [[geometry_optimization|previous exercise]]. Note that the equilibrium distance will depend on your basis set.
 +
 +<note important> The H$_2$ molecule does not have unpaired electrons. Remember to take out the LSD and MULTIPLICITY keywords.</note>
 +
 +===== Part II: Estimate the binding energy of H$_2$ =====
 +
 +Based on the formula for the //binding energy//, you can now update your table.
 +
 +\[ \sum E_\text{products} -  \sum E_\text{reactants} = E(H_2) - 2 \cdot E(H) \]
 +
 +
 +^ Basis set                  ^ Energy H [$E_h$] ^ Energy H$_2$ [$E_h$] ^ Distance H$_2$ [$Å$] ^ Binding Energy H$_2$ [$E_h$] ^
 +| mybasis (from given input) | ....             | ....              | ....            | ....                      |
 +| basis try 1                | ....             | ....              | ....            | ....                      |
 +| basis try 2                | ....             | ....              | ....            | ....                      |
 +| ....                       | ....             | ....              | ....            | ....                      |
 +| pc-0                       | ....             | ....              | ....            | ....                      |
 +| pc-1                       | ....             | ....              | ....            | ....                      |
 +| pc-2                       | ....             | ....              | ....            | ....                      |
 +| ....                       | ....             | ....              | ....            | ....                      |
 +
 +<note important>The binding energy is only significant if all terms were calculated with the same basis-set.</note>
 +
 +===== Part III: Questions =====
 +  - What is the effect of changing the exponents in a basis set?
 +  - What is the effect of adding p- and d-function to the basis set? Do H and H$_2$ respond differently?
 +
 +
 +===== Appendix: Literature Basis Sets =====
 +
 +<code>
 +H  pc-0
 +  2
 +  1  0  0  2  1
 +          4.34480000          0.07929900
 +          0.66049000          0.42422000
 +  1  0  0  1  1
 +          0.13669000          1.00000000
 +
 +H  pc-1
 +  3
 +  1  0  0  3  1
 +         12.25200000          0.02282200
 +          1.86870000          0.15564000
 +          0.41821000          0.48898000
 +  1  0  0  1  1
 +          0.10610000          1.00000000
 +  1  1  1  1  1
 +          1.00000000          1.00000000
 +
 +H  pc-2
 +  6
 +  1  0  0  4  1
 +         75.42300000          0.00240650
 +         11.35000000          0.01848700
 +          2.59930000          0.08974200
 +          0.73513000          0.28111000
 +  1  0  0  1  1
 +          0.23167000          1.00000000
 +  1  0  0  1  1
 +          0.07414700          1.00000000
 +  1  1  1  1  1
 +          1.60000000          1.00000000
 +  1  1  1  1  1
 +          0.45000000          1.00000000
 +  1  2  2  1  1
 +          1.25000000          1.00000000
 +
 +</code>
 +
  
exercises/2016_ethz_mmm/basis_sets.txt · Last modified: 2020/08/21 10:15 (external edit)