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AMPAC 8 User Manual |
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AMPAC 8 User Manual |
THERMO — Thermodynamics calculation is done.
THERMO THERMO(nnn) THERMO(nnn,mmm) THERMO(nnn,ooo,ppp)
This keyword calls for the thermodynamic values of internal energy, heat capacity, partition function, and entropy to be calculated for translational, rotational, and vibrational degrees of freedom. Special situations such as linear systems and transition states are automatically accommodated. The TRANS keyword may be used in conjunction with THERMO to remove modes corresponding to internal rotation that are present in some molecules. THERMO requires the computation of the Hessian matrix and so must accompanied by the keywords FORCE, IRC, NEWTON, or LTRD.
If THERMO alone is specified, the default values of the temperature range are assumed (200K to 400K in steps of 20 degrees). Three options exist for overriding the default temperature range, and they are given below. (Caution: The approximations used in the THERMO calculation are invalid below 100K.)
The thermodynamic quantities for a 200 degree range of temperatures, starting at nnn Kelvin in steps of 20 degrees, will be calculated.
The thermodynamic quantities for the temperature range limited by a lower bound of nnn Kelvin and an upper bound of mmm Kelvin will be calculated. The step size is calculated to give approximately 20 points, and a reasonable value for the step. The size of the step will be 1, 2, or 5, times a power of 10.
am1 rhf singlet t=auto truste force thermo rot=2 trans=2p-xylene Thermo with trans=2 to remove internal rotation of methyls C 0.000000 0 0.000000 0 0.000000 0 0 0 0
C 1.395052 1 0.000000 0 0.000000 0 1 0 0 C 1.396919 1 120.474038 1 0.000000 0 2 1 0 C 1.396919 1 119.051836 1 -0.106881 1 3 2 1 C 1.395052 1 120.474038 1 0.106881 1 4 3 2 C 1.396919 1 120.474038 1 0.108409 1 1 2 3 H 1.100167 1 119.542900 1 179.980911 1 1 6 5 H 1.100167 1 119.983003 1 -179.979770 1 2 1 6 H 1.100167 1 119.542900 1 -179.980911 1 4 3 2 H 1.100167 1 119.983003 1 179.979770 1 5 4 3 C 1.480664 1 120.472114 1 -179.388508 1 3 2 1 H 1.119254 1 109.937276 1 89.635686 1 11 3 2 H 1.116344 1 111.043245 1 -149.505323 1 11 3 2 H 1.116344 1 111.043245 1 -31.223306 1 11 3 2 C 1.480664 1 120.472114 1 -179.388508 1 6 1 2 H 1.116344 1 111.043245 1 -149.505323 1 15 6 1 H 1.116344 1 111.043245 1 -31.223306 1 15 6 1 H 1.119254 1 109.937276 1 89.635686 1 15 6 1 0 0.000000 0 0.000000 0 0.000000 0 0 0 0
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The keyword FORCE calls for a frequency calculation (in Cartesians) along with the generation of thermodynamic data. THERMO can only be requested if a keyword requiring computation of the Hessian (matrix of second derivatives) is used. In order to obtain correct results for the energy partition, the symmetry number for the point group must be given. The TS's point group is C2h , requiring ROT=2. The keyword TRANS=2 is optional as the new AMPAC automatically accounts for the presence of two negative eigenvalues. |
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This geometry was pre-optimized. If the geometry is not pre-optimized, then one of AMPAC's geometry optimizers (energy minimizers: TRUSTE, EF, NEWTON, BFGS, DFP; gradient minimizers: TRUSTG, TS, or LTRD) should be specified along with FORCE, so that the geometry will be optimized just prior to computing frequencies. |
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