We will investigate today a very important chemical reaction, the production of ethene (ethylene) from ethanol. Ethanol is heated with an excess of concentrated sulphuric acid at a temperature of 170°C. The gases produced are passed through sodium hydroxide solution to remove the carbon dioxide and sulphur dioxide produced from side reactions. Another way to favor this reaction is in presence of a catalyst surface, which makes the reaction exothermic even at room temperature, and the free energy barrier for the reaction is highly reduced, so to obtain reasonable reaction rates. The use of hematite (iron-based nanocrystal) as a catalyst is described computationally in the following paper by Lopes et al: 10.1039/c6ra08509a. We are interested in the gas phase reaction, in particular in the reactants and the products energy, to estimate the “energy of reaction”.

The reaction is the following: and this is the pictorial view in the gas phase:

In the supplementary material of the paper, which can be found here, several calculation with different methods ranging from DFT to hybrid methods to high-level methods are described, together with the basis set dependence of the results.

We will compare our results with the published ones

The input file structure is shown below:

   &DFT
      &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
 
#
# Include the exchange and correlation information
#
@INCLUDE './pbe.inc'
 
   &END DFT
 
 
   &SUBSYS                            ! This section defines the system
      &CELL                           ! Unit cell set up
         PERIODIC NONE                ! Non periodic calculation
         ABC 10 10 10                 ! Lengths of the cell vectors A, B, and C
      &END CELL
      &COORD                          ! This section specify all the atoms and their coordinates
  H         2.5558925119        4.9201502245        3.9999999733
  H         2.5617214834        3.0599837703        4.0000000267
  C         3.3235178526        3.9916405319        4.0000000002
  C         4.6493228423        3.9951429630        3.9999999995
  H         5.4118318595        4.9261779106        4.0000000269
  H         5.4167134504        3.0669045998        3.9999999735
      &END COORD
      &TOPOLOGY
          &CENTER_COORDINATES
          &END
      &END TOPOLOGY
 
      &KIND H                                      ! potential and basis for H
         &BASIS
@INCLUDE './H_631Gdp.inc'
         &END
         POTENTIAL ALL
         &POTENTIAL
          1    0    0
          0.20000000    0
         &END
      &END KIND
      &KIND C                         ! potential and basis for C
         &BASIS
@INCLUDE './C_631Gdp.inc'
         &END
         POTENTIAL ALL
         &POTENTIAL
            4    2    0
            0.34883045    0
         &END
      &END KIND
   &END SUBSYS
&END FORCE_EVAL                     ! This section defines method for calculating energy and forces
 
&GLOBAL                             ! Section with general information regarding which kind of simulation to perform an parameters for the whole PROGRAM
   PRINT_LEVEL LOW                  ! Global print level
   PROJECT c2h4                     ! Name of the project. This word will appear as part of a name of all ouput files (except main ouput file, specified with -o option)
   RUN_TYPE GEO_OPT                 ! Geometry optimization
&END GLOBAL