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exercises:2017_uzh_cp2k-tutorial:wfc [2017/07/07 12:22]
vrybkin
exercises:2017_uzh_cp2k-tutorial:wfc [2017/07/13 15:44] (current)
vrybkin
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 In order to go beyond GGA and hybrid DFT, one option is to use wave function correlation methods. Recently, second-order Møller-Plesset perturbation theory (MP2) and random phase approximation (RPA) have been added to CP2K . The implementations are aimed at condensed phase calculations,​ and in the case of MP2 provides energies, forces and stress, as well as electron (spin) densities at O(N^5) cost, while RPA provides energies at O(N^4) or O(N^3) cost. In order to go beyond GGA and hybrid DFT, one option is to use wave function correlation methods. Recently, second-order Møller-Plesset perturbation theory (MP2) and random phase approximation (RPA) have been added to CP2K . The implementations are aimed at condensed phase calculations,​ and in the case of MP2 provides energies, forces and stress, as well as electron (spin) densities at O(N^5) cost, while RPA provides energies at O(N^4) or O(N^3) cost.
  
-However, significant computational resources are needed for the condensed phase calculations. Therefore, we will perform the gas phase calculations in this tutorial, even though RI-GPW is not very efficient in this case.+However, significant computational resources are needed for the condensed phase calculations ​(for the overview see the corresponding lecture). Therefore, we will perform the gas phase calculations in this tutorial, even though RI-GPW is not very efficient in this case.
  
 **Some references:​** **Some references:​**
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 ===== 1. Task: Benzene dimer MP2 binding energy ===== ===== 1. Task: Benzene dimer MP2 binding energy =====
  
-Employ the provided input file to compute the benzene dimer binding energy. The provided dimer geometry is optimized already. To obtain the energy of the monomer, geometry optimization is necessary ​(or else is not). Perform a few optimization steps to see how much the energy changes and to calculate electron density (saved as .cube files) at the MP2 level.+Employ the provided input file to compute the benzene dimer binding energy. The provided dimer geometry is optimized already. To obtain the energy of the monomer, geometry optimization is in principle ​necessary, although the geometry of a benzene monomer must be close to the one in the dimer. This can be done by removing one of the benzene molecules editing the coordinates in the input. Perform a few optimization steps to see how much the energy changes and to calculate electron density (saved as .cube files) at the MP2 level. If energy does not change much, this means that the monomer structure is already close to the optimal. Compare the times needed for one geometry optimization step (energy+forces) for a monomer and energy for a dimer, as well as the relative timing for energy and forces evaluation for a monomer
  
-Topics+During the optimization of benzene, one will calculate gradient which, in turn, requires density matrices. Hence, one can calculate electronic densities. Add the following to the ''&​GLOBAL''​ section
-   * RI approach (''​RI_MP2_GPW'' ​and ''​RI_AUX_BASIS_SET''​) +<​code>​ 
-   * Wavelet solver (''​PSOLVER ​ WAVELET''​''​CENTER_COORDINATES''​) +&​PRINT ​       MEDIUM 
-   * gas phase HFX calculation ​ +&END 
-   * memory ​issues (''​FREE_HFX_BUFFER''​)+</​code>​ 
 +and the following lines to the ''​&DFT'' ​section 
 +<​code>​ 
 +&​PRINT 
 +  &​E_DENSITY_CUBE MEDIUM 
 +  &END 
 +&END 
 +</​code>​ 
 + 
 +Importantly,​ during the force calculations one will have to solve the coupled-perturbed equations invoking exact exchange calculations. If there is enough memory we can reuse the integrals from the HF calculation by setting the following keyword in the ''​&RI_MP2'' ​section: 
 +<​code>​ 
 +FREE_HFX_BUFFER .FALSE. 
 +</​code>​ 
 + 
 +Perform two optimizations setting ​''​FREE_HFX_BUFFER'' ​to ''​.TRUE.'' ​and ''​.FALSE.''​ Compare the overall timings and especially the times for performing Hartree-Fock exchange calculations:​ 
 +<​code>​ 
 +integrate_four_center ​              71 12.3    2.261    4.012  108.805 ​ 109.179 
 +</​code>​ 
 +The last number in the line is the real time of execution. The memory ​distribution between the RI-MP2 integrals and HFX integrals are tuned by the ''​MEMORY'' ​keyword in the ''&​WF_CORRELATION''​ section and the ''&​MEMORY''​ section in the ''&​HF''​ section: 
 +<​code>​ 
 +&​MEMORY 
 +  MAX_MEMORY ​ 1800 
 +&END 
 + 
 +</​code>​ 
 + 
 +At the optimized (or the most optimizedgeometry of benzene monomer perform a Hartree-Fock calculation to compare electron densities. Visualize them with VMD.  
 + ​Density differences can be computed with ''​cubecruncher''​ available in the executable directory.
  
 ===== 2. Task: Benzene monomer RPA energy: frequency integration ===== ===== 2. Task: Benzene monomer RPA energy: frequency integration =====
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 &MOTION &MOTION
  &​GEO_OPT  &​GEO_OPT
-   ​OPTIMIZER BFGS ! Good choice for '​small'​ systems ​(use LBFGS for large systems) +   ​OPTIMIZER BFGS ! Good choice for '​small'​ systems ​like benzene
-   ​MAX_ITER ​ 100+
    ​MAX_DR ​   [bohr] 0.003 ! adjust target as needed    ​MAX_DR ​   [bohr] 0.003 ! adjust target as needed
    &​BFGS    &​BFGS
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 </​code>​ </​code>​
  
-During the optimization of benzene, one will calculate gradient which, in turn, requires density matrices. Hence, one can calculate electronic densities. Add the following to the ''&​GLOBAL''​ section: 
-<​code>​ 
-&​PRINT ​       MEDIUM 
-&END 
-</​code>​ 
-and the following lines to the ''&​DFT''​ section 
-<​code>​ 
-&PRINT 
-  &​E_DENSITY_CUBE MEDIUM 
-  &END 
-&END 
-</​code>​ 
  
-Importantly,​ during the force calculations one will have to solve the coupled-perturbed equations invoking exact exchange calculations. If there is enough memory we can reuse the integrals from the HF calculation by setting the following keyword in the ''&​RI_MP2''​ section: 
-<​code>​ 
-FREE_HFX_BUFFER .FALSE. 
-</​code>​ 
  
   ​   ​
exercises/2017_uzh_cp2k-tutorial/wfc.1499430132.txt.gz · Last modified: 2017/07/07 12:22 by vrybkin