A stochastic search for AFIR paths starting from random mutual orientations and positions is performed when the MC-AFIR keyword is designated. An example for the Aldol reaction is shown below:
# MC-AFIR/B3LYP/6-31G
0 1
C 0.000000 0.000000 -0.542432 1
O 0.000000 0.000000 0.689131 1
H 0.000000 0.933503 -1.129226 1
H 0.000000 -0.933503 -1.129226 1
C 0.000000 0.449088 0.000000 2
C 1.229479 -0.074689 0.000000 2
O -1.202903 -0.246241 0.000000 2
H -0.199138 1.513645 0.000000 2
H 1.411363 -1.146198 0.000000 2
H 2.098519 0.571041 0.000000 2
H -1.064389 -1.214959 0.000000 2
Options
NFault = 50
Add Interaction
Fragm.1 = 1,2
Fragm.2 = 5-7,11
1 2
GAMMA = 200
END
The last integer in each Cartesian coordinate is for random distribution of each molecule; in this case, HCHO is part #1 and H2C=CHOH is part #2 (see Part designation for random structure generation).
The NFault = 50 keyword provides a stopping criterion, where the stochastic search will be terminated when the last 50 AFIR paths give no new product. In a MC-AFIR calculation, you need to specify a stopping criterion by using NFault = n or NSample = n keyword.
There are four lines between the Add Interaction … END keywords:
(1) Fragm.1 = 1,2 specifies that atoms 1 and 2 belong to fragment #1 (atoms belonging to the fragment A of the AFIR function),
(2) Fragm.2 = 5-7,11 specifies that atoms 5–7 and 11 belong to fragment #2 (atoms belonging to the fragment B of the AFIR function),
(3) the artificial force is applied between the fragments #1 and #2,
(4) the initial γ value is set to 200s kJ/mol and is gradually increased to 200 kJ/mol, where s is the random number between 0 and 1.
The history of AFIR minimizations and corresponding AFIR path profiles appear in xxx_EQn.log files. For example, this AFIR minimization gives the aldol addition product (3-hydroxypropanal, CHOCH2CH2OH) from HCHO and H2C=CHOH.
# Geometry optimization starting from a random structure
OPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTO
# ITR. 0
C -0.540936514510 0.642893723683 0.666366212385
O 0.026751246314 0.125252441047 1.628928174905
H -0.105004419262 1.492775128740 0.115530615210
H -1.517832851012 0.286285985996 0.299951804105
C 0.568973384233 -0.053494217478 -0.791852842498
C -0.262880591377 0.673833504707 -1.543500569145
O 0.268899839016 -1.228357438722 -0.113538516775
H 1.607310832988 0.204482332750 -0.623802280651
H -1.302735396999 0.400164089027 -1.701678825180
H 0.086155801452 1.577613934590 -2.026773044611
H -0.663847278893 -1.495343702957 -0.241217177722
Item Value Threshold
ENERGY -268.019793471042
Spin(**2) 0.000000000000
LAMDA -0.352906091272
TRUST RADII 0.100000000000
STEP RADII 0.099999989666
Maximum Force 0.210290244955 0.000060000000
RMS Force 0.060599825781 0.000040000000
Maximum Displacement 0.020532281193 0.000300000000
RMS Displacement 0.009137884037 0.000200000000
NORMAL MODE EIGENVALUE : N_MODE = 27
-0.014681504 -0.008511168 -0.000178336 0.011266906 0.017799578
0.027561925 0.032817954 0.049674405 0.059800244 0.095898853
0.122765847 0.129883647 0.137069574 0.162066311 0.173561445
0.189233172 0.205047624 0.261867122 0.323541243 0.396700830
0.593958115 0.790149481 0.819969212 0.961279874 1.069551765
1.449123479 1.536917879
# ITR. 1
︙
# ITR. 121
C -0.786968582858 0.757425948976 0.321251614371
O -1.270570428742 -0.501447730380 0.878342487417
H -0.021078167273 1.192492267741 0.981359179036
H -1.651398924495 1.425474886429 0.344920923743
C 0.936913938706 -0.285129777403 -1.184527664387
C -0.273258397260 0.613550446855 -1.042373355847
O 1.390920127639 -0.987430927167 -0.268372420966
H 1.413620884046 -0.300743880949 -2.180683453084
H -1.049536329939 0.202185768103 -1.709407370810
H -0.012032370467 1.591764473351 -1.477911262354
H -0.511757697409 -1.082035694189 1.005814872905
Item nbsp; Value Threshold
ENERGY -268.147165081138
Spin(**2) 0.000000000000
LAMDA 0.000000047011
TRUST RADII 0.010000000000
STEP RADII 0.000038327528
Maximum Force 0.000007800063 0.000060000000
RMS Force 0.000002700314 0.000040000000
Maximum Displacement 0.000016894323 0.002307673758
RMS Displacement 0.000006184179 0.001538449172
NORMAL MODE EIGENVALUE : N_MODE = 27
0.002948307 0.003514348 0.011132064 0.017382588 0.028646131
0.042045668 0.047591209 0.056494074 0.070584220 0.077213762
0.099431003 0.105421624 0.144396599 0.178250796 0.195439892
0.230543169 0.266132098 0.277794184 0.432649094 0.562201985
0.693605925 0.783379895 0.814074876 0.883169566 0.916859801
1.018291727 1.504266977
=========================================================================
Optimized structure, SYMMETRY = C1
C -0.786968582858 0.757425948976 0.321251614371
O -1.270570428742 -0.501447730380 0.878342487417
H -0.021078167273 1.192492267741 0.981359179036
H -1.651398924495 1.425474886429 0.344920923743
C 0.936913938706 -0.285129777403 -1.184527664387
C -0.273258397260 0.613550446855 -1.042373355847
O 1.390920127639 -0.987430927167 -0.268372420966
H 1.413620884046 -0.300743880949 -2.180683453084
H -1.049536329939 0.202185768103 -1.709407370810
H -0.012032370467 1.591764473351 -1.477911262354
H -0.511757697409 -1.082035694189 1.005814872905
ENERGY = -268.147165081138 (-268.266268520120 : 0.000000000000)
Spin(**2) = 0.000000000000
GRADIENT VECTOR
0.000001792320
-0.000000951514
︙
-0.000004418902
Stationary point was found
OPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTOPTO
---Profile of AFIR path
Itr. Length (ang) Energy (real) Energy (fit)
0 0.000000000000 -268.091781022859 -268.091843039207 -0.79
1 0.052493147309 -268.106691683549 -268.106635647314 -0.82
2 0.153933590264 -268.130250034996 -268.130176731684 -0.84
︙
121 7.376087521129 -268.266268520120 -268.266221739599 -1.00
---Approximate TS geometry (between 53 and 54)
C -0.769043350099 0.836174754828 0.553666033676
O -0.946931216613 -0.363105624661 1.069183231473
H 0.081022489940 1.436287874035 0.914124669930
H -1.652266963961 1.448484153975 0.333105701673
C 0.797124542080 -0.256455727715 -1.107244840230
C -0.326367647985 0.553591793619 -1.306893151361
O 0.713078562496 -1.378208111551 -0.412787655918
H 1.808089199114 0.082216129416 -1.330941548075
H -1.278879764100 0.062283179364 -1.488712985732
H -0.184297425384 1.470276554491 -1.875647339676
H -0.076674373533 -1.265439194417 0.320561434271
ENERGY = -268.211573137597
---Approximate EQ geometry (121)
C -0.786968582858 0.757425948976 0.321251614371
O -1.270570428742 -0.501447730380 0.878342487417
H -0.021078167273 1.192492267741 0.981359179036
H -1.651398924495 1.425474886429 0.344920923743
C 0.936913938706 -0.285129777403 -1.184527664387
C -0.273258397260 0.613550446855 -1.042373355847
O 1.390920127639 -0.987430927167 -0.268372420966
H 1.413620884046 -0.300743880949 -2.180683453084
H -1.049536329939 0.202185768103 -1.709407370810
H -0.012032370467 1.591764473351 -1.477911262354
H -0.511757697409 -1.082035694189 1.005814872905
ENERGY = -268.266221739599
The approximate product and TS structures will be listed in xxx_EQ_list.log and xxx_TS_list.log files, respectively. These approximate structures may be optimized either manually one by one (by using MIN, SADDLE or LUP keyword), or automatically using the RePATH keyword.