Geometry Optimization for Charged Molecules

[jayeshjawandhia]

Hi,
We need your help in figuring out how we can use dalton to find out the geometry of a charged molecule using the neutral molecule structure. Lets say I have the .mol structure of C3H6O (Acetone) and I need to figure out the geometry of C3H6O+, then what all functions will I need to use for finding its geometry using DFT in Dalton.
Please help!
Thanks
Jayesh
IIT Delhi

[hjaaj]

You can either enter the molecular charge in the .mol file, or you can specify the number of doubly and singly occupied orbitals under *SCF in the .dal file. If you use the first option, it will be with one singly occupied orbital for odd-electron cases, to get e.g. a quartet high-spin calculation you have to use the second option.

[jayeshjawandhia]

Yes so I am specifying the molecular charge in the .dal file like attached.But how it should I go about selecting appropriate basis, should I use a common basis for variety of molecules or there is a rule in selecting the basis? Also if you could please check my input dalton file for geometry optimization of Triethyleamine given below that'll really help me get going.

***DALTON INPUT FOR GEOMETRY OPTIMIZATION OF TEA TO FIND TEA+ STRUCTURE***

BASIS
3-21G**
TEA
Generated by the Dalton Input File Plugin for Avogadro
Atomtypes=3 Angstrom Charge=1 Nosymmetry
Charge=7.0 Atoms=1
N -0.00490 0.00210 0.18010
Charge=6.0 Atoms=6
C -1.34750 -0.32930 -0.29550
C 0.38120 1.33900 -0.26960
C 0.96180 -0.99230 -0.28420
C -2.37510 0.65960 0.22810
C 1.77480 1.70050 0.21590
C 0.60980 -2.37970 0.22540
Charge=1.0 Atoms=15
H -1.39660 -0.37020 -1.39100
H -1.66490 -1.30560 0.08420
H 0.33630 1.43380 -1.36190
H -0.28570 2.09610 0.15570
H 1.04230 -1.00780 -1.37850
H 1.95880 -0.78490 0.11700
H -2.27000 0.82260 1.30630
H -2.32650 1.62520 -0.28450
H -3.38340 0.26650 0.05510
H 1.90540 1.48270 1.28150
H 2.56160 1.19540 -0.35280
H 1.93990 2.77590 0.08250
H 0.38660 -2.37500 1.29790
H -0.23370 -2.82260 -0.31290
H 1.46160 -3.05250 0.07350
**DALTON INPUT
.OPTIMIZE
**WAVE FUNCTIONS
.DFT
B3LYP
**END OF DALTON INPUT

[taylor]

Please post files separately --- pasting them inline messes up the formatting and makes the message harder to read. Note that program output contains the input files, so if you have an output file just upload that.

For cations it is normal practice to use whatever basis you use for the corresponding neutral (anions are a different matter). Be aware that
1) There is no UHF option in Dalton, so the only possibility is high-spin restricted open-shell SCF (or MCSCF, of course).
2) I am pretty sure that if you treat an open-shell system with DFT, you need to specify .DIRECT under **DALTON INPUT.
3) There is no open-shell coupled-cluster capability (this is not quite true because one can treat triplet states by CC response, but that is not relevant for ionization from a closed-shell neutral molecule).

Best regards
Pete