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Table of Contents
Reaction Energy
In this exercise, you will calculate the reaction energy for the mehane combustion reaction:
Ground state oxygen, O2, is a triplet diradical, a property which can explain why liquid oxygen is paramagnetic and attracted to the poles of a magnet.
For this reason, to get the energy of the O2 molecule, a LSD calculation is required.
1.Step
Run a single point calculation for CH4, using the given input file. Note that the file contains explicit basis sets and potential for all-electron calculations. An explanation of the basis set formats is given here: Basis Sets
- CH4.inp
&GLOBAL PROJECT CH4 RUN_TYPE ENERGY &END GLOBAL &FORCE_EVAL METHOD Quickstep ! Electronic structure method (DFT,...) &DFT &POISSON ! Solver requested for non periodic calculations PERIODIC NONE PSOLVER MT ! Type of solver &END POISSON &QS ! Parameters needed to set up the Quickstep framework METHOD GAPW ! Method: gaussian and augmented plane waves &END QS &SCF ! Parameters controlling the convergence of the scf. This section should not be changed. MAX_ITER_LUMOS 5000 EPS_SCF 1.0E-6 SCF_GUESS ATOMIC MAX_SCF 60 EPS_LUMOS 0.0001 &OUTER_SCF EPS_SCF 1.0E-6 MAX_SCF 6 &END &OT PRECONDITIONER FULL_ALL ENERGY_GAP 0.1 &END OT &END SCF &XC ! Parametes 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. EPS_SCHWARZ 1.0E-10 ! Threshold specification &END SCREENING &END HF &END XC &END DFT &SUBSYS &CELL ABC 10 10 10 PERIODIC NONE ! Non periodic calculations. That's why the POISSON scetion is needed &END CELL &TOPOLOGY ! Section used to center the atomic coordinates in the given box. Useful for big molecules &CENTER_COORDINATES &END &END &COORD C 4.6470817907 5.0564551166 5.2030612698 H 5.7285481608 5.0545340413 5.2150365876 H 4.2810776129 5.8762854944 5.8061577262 H 4.2804181558 4.1216454580 5.6048052221 H 4.2983162673 5.1733905029 4.1860324290 &END COORD &KIND H !Potential and basis sets for H &BASIS 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 &END POTENTIAL ALL &POTENTIAL 1 0 0 0.20 0 &END &END KIND &KIND C !Potential and basis sets for C &BASIS 9 1 0 0 8 2 7857.10000000 0.00056825 0.00000000 1178.70000000 0.00439150 -0.00000059 268.32000000 0.02250400 -0.00006275 75.94800000 0.08665300 -0.00075773 24.55900000 0.24405000 -0.00733080 8.62120000 0.44148000 -0.03893200 3.12780000 0.35332000 -0.08890800 0.82202000 0.00000000 0.21689000 1 0 0 1 1 0.33017000 1.00000000 1 0 0 1 1 0.11463000 1.00000000 1 1 1 4 1 33.77500000 0.00602940 7.67660000 0.04322800 2.23570000 0.16301000 0.76447000 0.36504000 1 1 1 1 1 0.26232000 1.00000000 1 1 1 1 1 0.08463800 1.00000000 1 2 2 1 1 1.40000000 1.00000000 1 2 2 1 1 0.45000000 1.00000000 1 3 3 1 1 0.95000000 1.00000000 &END POTENTIAL ALL &POTENTIAL 4 2 0 0.34883045 0 &END &END KIND &END SUBSYS &END FORCE_EVAL
If the calculation was performed correctly, the total energy of the CH4 molecule is printed in the output file.
**** **** ****** ** PROGRAM STARTED AT ***** ** *** *** ** PROGRAM STARTED ON ** **** ****** PROGRAM STARTED BY ***** ** ** ** ** PROGRAM PROCESS ID **** ** ******* ** PROGRAM STARTED IN ..... ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.): ..... **** **** ****** ** PROGRAM ENDED AT ***** ** *** *** ** PROGRAM RAN ON ** **** ****** PROGRAM RAN BY ***** ** ** ** ** PROGRAM PROCESS ID **** ** ******* ** PROGRAM STOPPED IN
2.Step
Modify the input in order to perform the same calculation for:
- H2O
- CO2
- O2 TRIPLET
Remember that the O2 ground state is a triplet state, with non paired electrons (MULTIPLICITY = 3). The LSD and MULTIPLICITY keywords are needed in the DFT section:
METHOD Quickstep &DFT LSD ! Requests a spin-polarized calculation for unpaired electrons MULTIPLICITY 3 ! Multiplicity = 2S+1 (S= total spin momentum) ...
Another example can be found here Basis Sets
3.Step
At the end, you should get a table like:
Species | Total Energy |
---|---|
CH4 | … |
O2 | … |
H2O | … |
CO2 | … |
Now you can compute the overall reaction energy.
Questions
- Report the total energy for all the molecules, and the overall reaction energy for CH4 combustion.
- (Optional) Compute the total enery for O2 singlet and the energy difference with O2 triplet.
Additional material
- O BASIS SET
- O POTENTIAl
- O2 coordinates
- CO2 coordinates
- CH4 coordinates