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Output File

This page walks through the key parts of the Gaussian output for the NMR calculation.

Normal Termination

 Normal termination of Gaussian 09 at Wed Jul 15 23:23:59 2026.

A single, clean termination — since this is a single-point property calculation, there's no optimization convergence to check first, unlike the Transition State or Optimization outputs.

The Shielding Tensor Block

The calculation reports a full magnetic shielding tensor for every atom in the molecule:

 SCF GIAO Magnetic shielding tensor (ppm):
      1  C    Isotropic =    24.5951   Anisotropy =   112.7607
   XX=    13.4590   YX=   -54.2336   ZX=    -0.0452
   XY=   -34.3530   YY=   -39.4425   ZY=    -0.1073
   XZ=    -0.0360   YZ=    -0.0761   ZZ=    99.7688
   Eigenvalues:   -64.5819    38.5983    99.7689
Quantity Meaning
Isotropic The orientation-averaged shielding constant — one-third of the trace of the tensor (see Isotropic Shielding and Anisotropy). This is the value most directly related to the observed chemical shift.
Anisotropy How much the shielding varies with orientation — the difference between the tensor's largest and average principal components.
XX, YX, ZX, ... The nine Cartesian components of the shielding tensor.
Eigenvalues The tensor's three principal values, obtained by diagonalizing it — these are what "isotropic" and "anisotropy" above are actually computed from.

Isotropic Shielding for All Ten Atoms

Atom Element Isotropic (ppm) Anisotropy (ppm)
1 C 24.5951 112.7607
2 H 24.0427 4.2554
3 O 77.6702 217.6326
4 H 19.3382 16.8258
5 O −74.8922 523.0746
6 C 24.5951 112.7607
7 H 24.0427 4.2554
8 O 77.6702 217.6326
9 O −74.8922 523.0746
10 H 19.3382 16.8258

Atoms 1–5 and 6–10 match exactly, atom-for-atom — this is the symmetry of the formic acid dimer showing up directly in the calculated properties, and it's a useful sanity check: if the two monomers didn't give matching values, that would point to either a geometry that isn't as symmetric as intended, or an unconverged SCF.

The large spread in isotropic values — from about −75 ppm for the bridging carbonyl oxygen (atom 5) up to about 78 ppm for the other oxygen (atom 3) — reflects how differently these two oxygens sit within the hydrogen-bonded dimer, even though both are formally "carboxylic acid oxygens."

From Shielding to Chemical Shift

The numbers above are absolute shielding constants, not chemical shifts. Experimental NMR spectra report shifts (δ, in ppm) relative to a reference compound — commonly tetramethylsilane (TMS) for ¹H and ¹³C. Converting requires a separate NMR calculation on the reference compound, at the same method and basis set, then taking the difference:

δ(sample) = σ(reference) − σ(sample)

See Referencing Chemical Shifts for the full picture, including why the method and basis set must match between the two calculations.