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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_simple4 RUN_TYPE ENERGY PRINT_LEVEL MEDIUM &END GLOBAL &FORCE_EVAL METHOD Quickstep ! Electronic structure method (DFT,...) &DFT BASIS_SET_FILE_NAME EMSL_BASIS_SETS POTENTIAL_FILE_NAME POTENTIAL &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 ! 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 &END COORD &KIND H POTENTIAL ALL BASIS_SET pc-1 &END KIND &KIND C POTENTIAL ALL BASIS_SET pc-1 &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
For O2 triplet, 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 pc-2 9 1 0 0 8 2 14782.00000000 0.00053519 0.00000000 2217.30000000 0.00413750 -0.00000193 504.74000000 0.02124500 -0.00005796 142.87000000 0.08245300 -0.00079494 46.30000000 0.23671000 -0.00731250 16.33700000 0.44039000 -0.04057400 5.98280000 0.36465000 -0.09159400 1.67180000 0.00000000 0.20940000 1 0 0 1 1 0.64662000 1.00000000 1 0 0 1 1 0.21669000 1.00000000 1 1 1 4 1 60.42400000 0.00689490 13.93500000 0.04900500 4.15310000 0.18255000 1.41580000 0.37633000 1 1 1 1 1 0.47549000 1.00000000 1 1 1 1 1 0.14529000 1.00000000 1 2 2 1 1 2.20000000 1.00000000 1 2 2 1 1 0.65000000 1.00000000 1 3 3 1 1 1.10000000 1.00000000
- O potential
#O ALLELECTRON ALL 4 4 0 0.24762086 0
- O2 coordinates
O 4.4705353672 4.7577727756 4.9999951398 O 5.5294646329 5.2422272244 5.0000048599
- CO2 coordinates
- H2O coordinates