exercises:2016_ethz_mmm:basis_sets
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— | exercises:2016_ethz_mmm:basis_sets [2020/08/21 10:15] (current) – created - external edit 127.0.0.1 | ||
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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 [[: | ||
+ | |||
+ | ===== 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 | ||
+ | |||
+ | & | ||
+ | METHOD Quickstep | ||
+ | | ||
+ | &DFT | ||
+ | LSD ! Requests a spin-polarized calculation for non paired electrons | ||
+ | MULTIPLICITY 2 ! Multiplicity = 2S+1 (S= total spin momentum) | ||
+ | & | ||
+ | PERIODIC NONE | ||
+ | PSOLVER | ||
+ | &END POISSON | ||
+ | & | ||
+ | METHOD GAPW ! Method: gaussian and augmented plane waves | ||
+ | &END QS | ||
+ | & | ||
+ | & | ||
+ | &END XC_FUNCTIONAL | ||
+ | & | ||
+ | & | ||
+ | EPS_SCHWARZ 1.0E-10 | ||
+ | &END SCREENING | ||
+ | &END HF | ||
+ | &END XC | ||
+ | &END DFT | ||
+ | | ||
+ | &SUBSYS | ||
+ | & | ||
+ | & | ||
+ | &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 | ||
+ | | ||
+ | &END COORD | ||
+ | &KIND H | ||
+ | & | ||
+ | 2 | ||
+ | 1 0 0 1 1 | ||
+ | 0.35 1 | ||
+ | 1 0 0 1 1 | ||
+ | 0.6 1 | ||
+ | & | ||
+ | | ||
+ | & | ||
+ | | ||
+ | | ||
+ | & | ||
+ | &END KIND | ||
+ | &END SUBSYS | ||
+ | &END FORCE_EVAL | ||
+ | |||
+ | </ | ||
+ | |||
+ | ==== 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 | ||
+ | | 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.. </ | ||
+ | |||
+ | ==== 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> | ||
+ | |||
+ | ===== 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> | ||
+ | |||
+ | ===== 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 ===== | ||
+ | |||
+ | < | ||
+ | H pc-0 | ||
+ | 2 | ||
+ | 1 0 0 2 1 | ||
+ | 4.34480000 | ||
+ | 0.66049000 | ||
+ | 1 0 0 1 1 | ||
+ | 0.13669000 | ||
+ | |||
+ | H pc-1 | ||
+ | 3 | ||
+ | 1 0 0 3 1 | ||
+ | | ||
+ | 1.86870000 | ||
+ | 0.41821000 | ||
+ | 1 0 0 1 1 | ||
+ | 0.10610000 | ||
+ | 1 1 1 1 1 | ||
+ | 1.00000000 | ||
+ | |||
+ | H pc-2 | ||
+ | 6 | ||
+ | 1 0 0 4 1 | ||
+ | | ||
+ | | ||
+ | 2.59930000 | ||
+ | 0.73513000 | ||
+ | 1 0 0 1 1 | ||
+ | 0.23167000 | ||
+ | 1 0 0 1 1 | ||
+ | 0.07414700 | ||
+ | 1 1 1 1 1 | ||
+ | 1.60000000 | ||
+ | 1 1 1 1 1 | ||
+ | 0.45000000 | ||
+ | 1 2 2 1 1 | ||
+ | 1.25000000 | ||
+ | |||
+ | </ | ||
+ | |||
exercises/2016_ethz_mmm/basis_sets.txt · Last modified: 2020/08/21 10:15 by 127.0.0.1