NMR calculation of Si(CH3)4 not converged

[hjaaj]

Once more, please attach your dalton output instead of asking someone to repeat. You must change from "Quick Reply" to "Full Editor & Preview" in order to attach files.

[xiongyan21]

Deleted.

[xiongyan21]

The shielding constants of six hydrogen atoms in C2H6 in CCl4 are the same, thus what is wrong for the NMR calculation of Si(CH3)4? I will repeat it.

Very Best Regard!

[taylor]

I do not understand why you post the output file of a calculation you say has worked, but you do not post the output file of the calculation (TMS) you have a question about? If the problem is with a TMS calculation, and you want some assistance with this problem, surely the best thing to do is to post the TMS output? As I have remarked many times on this forum, the Dalton developers share many skills, but telepathy is not one of them...

Best regards
Pete

[xiongyan21]

Dear Profs. Jensen and Remigio
With the following PCMCAV
.INA
1
2
3
4
5
.RIN
1.8
2.1
2.1
2.1
2.1

The following can be got
@2 H 33.8213
@2 H 33.7630
@2 H 33.7506
@2 H 35.0592
@2 H 34.1591
@2 H 35.1911
@2 H 34.6104
@2 H 35.9867
@2 H 34.6842
@2 H 35.7429
@2 H 35.1618
@2 H 35.3002

I will optimize it with symmetry and retry.

Very Best Regards!

[taylor]

For TMS, B3LYP/pcS-1 in CCl₄ (geometry optimized using B3LYP/pc-1, I think) I obtain
+--------------------------------+
! Summary of chemical shieldings !
+--------------------------------+

@1 Definitions from J. Mason, Solid state Nuc. Magn. Res. 2 (1993), 285

@1 London orbitals (GIAOs) has been used.

@1 atom shielding dia para skew span (aniso asym)
@1 ----------------------------------------------------------------------------
@1 C _1 179.4531 360.1113 -180.6582 0.9967 25.3710 25.3501 0.0025
@1 C _2 179.4531 360.1113 -180.6582 0.9967 25.3710 25.3501 0.0025
@1 C _3 179.4531 360.1113 -180.6582 0.9967 25.3710 25.3501 0.0025
@1 C _4 179.4531 360.1113 -180.6582 0.9967 25.3710 25.3501 0.0025
@1 SI 377.8445 995.1032 -617.2587 -0.8761 0.1417 0.0753 2.6501
@1 H1 _1 30.9626 17.2291 13.7334 0.5009 10.2081 8.9345 0.4277
@1 H1 _2 30.9626 17.2291 13.7334 0.5009 10.2081 8.9345 0.4277
@1 H1 _3 30.9626 17.2291 13.7334 0.5009 10.2081 8.9345 0.4277
@1 H1 _4 30.9626 17.2291 13.7334 0.5009 10.2081 8.9345 0.4277
@1 H2 _1 30.9622 17.2291 13.7331 0.4975 10.2116 8.9286 0.4311
@1 H2 _2 30.9622 17.2291 13.7331 0.4975 10.2116 8.9286 0.4311
@1 H2 _3 30.9622 17.2291 13.7331 0.4975 10.2116 8.9286 0.4311
@1 H2 _4 30.9622 17.2291 13.7331 0.4975 10.2116 8.9286 0.4311
@1 H3 _1 30.9621 17.2291 13.7329 0.4977 10.2114 8.9290 0.4309
@1 H3 _2 30.9621 17.2291 13.7329 0.4977 10.2114 8.9290 0.4309
@1 H3 _3 30.9621 17.2291 13.7329 0.4977 10.2114 8.9290 0.4309
@1 H3 _4 30.9621 17.2291 13.7329 0.4977 10.2114 8.9290 0.4309

I would regard discrepancies of less than 2 parts in a million as very satisfactory, especially since this is a DFT calculation and thus inolves numerical integration. I suspect an SCF calculation would lead to even smaller discrepancies.

Best regards
Pete

[xiongyan21]

I think perhaps it is not the basis set that makes a difference. Could you please post you input and output file here because even almost identical, your shielding constants are a little low?

Very Best regards!

[xiongyan21]

I am now using mp2, aug-cc-pVDZ and generator=1 xy to optimize Si(CH3)4.

Very Best Regards!

[taylor]

The values are irrelevant to your original question, which was that you apparently did not obtain 12 equal hydrogen shieldings. This must reflect some problem with your input, because as you see I do obtain 12 equal shieldings. Since you are unwilling to post your output file, despite multiple requests to do so, there is nothing more I can do. The same applies to your query about the MP2 optimization.

Best regards
Pete

[taylor]

I did not see your additional message that came in while I was writing mine, sorry. I myself used
Generators=2 XY XZ
to specify D₂ symmetry. Exact T_d symmetry is then trivially achieved for the SiC₄ part by putting the single distinct carbon at a point with the same x, y, and z coordinates (and the Si at the origin, of course). The H atoms are trickier because there are three distinct atoms to specify: if we imagine a C atom to be at the vertex of a cube in which the other carbons occupy alternate vertices, then the CH bonds can either project onto the cube edges, or project onto the bisectors of the cube faces (achieved by rotating the CH₃ groups by 30 degrees from the previous orientation). The latter geometry is the global minimum if I recall. Needless to say, care must be taken to ensure that the CH bond lengths are equal and the HCH bond angles are all equal in the distinct methyl group.

Best regards
Pete

[xiongyan21]

Dear Dr. Taylor
Thanks a lot for your help.
MP2 and aug-cc-pVDZ for this molecule is very time-demanding, thus I am now using b3lyp and aug-cc-pVDZ, and the generators identical to yours.
The initial geometry is drawn by Avagodro without a template which cannot guarantee a successful optimization. It seems it gets stuck at
...

Nuclear contribution to dipole moments
--------------------------------------

All dipole components are zero by symmetry
...

indicating perhaps the symmetry is not suitable for the molecule drawn, thus I first use no symmetry again.


Very Best Regards!

[xiongyan21]

Using nosymmetry, geometry optimization moves on
...
.--------------------------------------------.
| Starting in Wave Function Section (SIRIUS) |
`--------------------------------------------'

* Read MO coefficients from SIRIUS.RST with label "NEWORB " and header info: 18Jul20 FOCKDIIS

**********************************************************************
*SIRIUS* a direct, restricted step, second order MCSCF program *
**********************************************************************

(Wave function specification suppressed here, see output above for initial geometry.)

...
Very Best Regards!

[xiongyan21]

It seems that neither the basis set nor the symmetry which makes a difference, because with aug-cc-pVDZ and b3lyp nosymmetry optimized geometry obtained by Dalton2018, 3-21G(just for trying) and b3lyp in CCl4 gives negligible differences of the shielding constants among all 12 hydrogen atoms around 32.898ppm, meaning for this kind of calculation with Dalton2018, the best way is using a geometry optimized by DALTON2018.

Very Best Regard!