Could you please guide me on how to apply spin constraints to a dimer molecule, where one part is in the ground state and the other part is in the singlet excited state, using CDFT?
I have attempted various approaches, but the calculation yields spin values of 1 for the singlet part and -1 for the ground state part.
$cdft
1
0 1 18 s
1 19 36 s
$end
From my understanding, a value of 1 typically corresponds to a singlet, while 0 would represent the ground state.
Thank for your time.
I think you need to be more specific about what you are trying to accomplish, and also provide a complete input file. CDFT is a ground-state method. It is probably possible to use it for excited states within a Delta-SCF framework but that has to be done carefully and I can’t give instructions without more information.
Thank you Prof. Herbert for your time.
I have a dimer molecule in a stacked configuration, with one fragment in the ground state (with a spin of 0) and the other fragment in the singlet excited state (with a spin of 1). For the entire molecule, the total spin multiplicity is set to one(in the input text file). I am trying to model the system using CDFT and my input file is as follows:
$molecule
0 1
C 1.4406305753640165 -1.2058577096336214 0.1168728396785399
C 0.7610824726896654 -2.4032145743568414 0.1053645762119988
C -0.6555287956446529 -2.4202673695678247 0.1003213967781785
C -1.3639412261408619 -1.2396105322328810 0.1068755951566832
C -1.3939336240237241 1.2478376020935251 0.1137069023312519
C -0.6928901478062796 0.0123182493695870 0.1132368844316397
C 0.7394151100067509 0.0295548931038575 0.1185283589560915
C 1.4105583893357290 1.2813728876113384 0.1243384949349360
C 0.7024144920274809 2.4621818413574230 0.1196815964469848
C -0.7141977773427012 2.4452163180477147 0.1138225204594883
H 1.3091590888961562 -3.3404703406532414 0.1066814099920432
H -1.1810674456842269 -3.3703076296005303 0.0981355380578570
H 1.2280255213609113 3.4121512199411770 0.1272631687361332
H -1.2623266785428719 3.3824396729891499 0.1165694201567211
H -2.4803332953039252 1.2313445514536399 0.1205007120432589
H -2.4505486775821916 -1.2500751156692871 0.1139204424600061
H 2.5270498099075849 -1.1898326847052976 0.1319451430759121
H 2.4970453090221159 1.2908565154351226 0.1397781959406416
H 2.4914027452237022 -1.2392349451611466 3.8329482517441962
H 2.4946011301130935 1.2422732385717004 3.8406308440186332
C 1.4048464405260881 -1.2408559776862771 3.8460781656768557
C 1.4080417154716054 1.2468073828678705 3.8532760394594820
H 1.2456146816074878 -3.3733013391493696 3.8460734956963756
H 1.2530824815682351 3.3799702442055417 3.8656626344799303
C 0.7094323011698542 -2.4292301478993195 3.8507718666335382
C 0.7203805589371134 0.0037818052910601 3.8493025227106639
C 0.7154375227944707 2.4366963634371381 3.8644751327185465
C -0.7072694134155275 -2.4278464167054787 3.8528357389457333
C -0.7120198212898338 0.0051908066762901 3.8506818769900577
C -0.7013049869371563 2.4380935066554019 3.8653736462360242
C -1.3997183460428866 -1.2377424525658083 3.8492390448214735
H -1.2451792205292453 -3.3709652345708356 3.8499381518960880
C -1.3966805472172950 1.2497913853807456 3.8554137212823960
H -1.2372833237584100 3.3823011856684206 3.8670996383578262
H -2.4863085876688751 -1.2326628689860513 3.8390032955779150
H -2.4832684310914344 1.2484256689870863 3.8445727369058602
$end
$rem
jobtype opt
METHOD B3LYP
BASIS 6-31G(D)
XC_GRID 000099000590
DFT_D D3_BJ
UNRESTRICTED TRUE
max_scf_cycles 200
GEOM_OPT_MAX_CYCLES 200
SCF_ALGORITHM DIIS
SCF_GUESS SAD
SCF_CONVERGENCE 8
!THRESH 14
SCF_FINAL_PRINT 1
mem_static 500
MEM_TOTAL 32000
SYMMETRY FALSE
SYM_IGNORE TRUE
CDFT TRUE
CDFT_THRESH 7
CDFT_BECKE_POP TRUE
BECKE_SHIFT UNSHIFTED
$end
$cdft
1
0 1 18 s
1 19 36 s
$end
Hello soniadas1994,
Such constraint is not possible because the dimer has no net spin. See the explanation after example 5.23 (5.11.4 Examples‣ 5.11 Methods Based on “Constrained” DFT ‣ Chapter 5 Density Functional Theory ‣ Q-Chem 6.2 User’s Manual) for the charge constraint. In order to satisfy the total spin of the dimer, the first fragment must be -1.