SM1A — Superseded by SM5.2, SM5.2R, SM5C, and SM5CR.




SM1a is no longer available and SM5.2, SM5.2R, SM5C, or SM5CR should be used instead.

This keyword activates one of the AMSOL models contributed by D.G. Truhlar, C.J. Cramer, and G.C. Lynch. (See Chapter 15, AMSOL Model Module for a more complete description of the AMSOL methods and additional dedicated keywords.) The keyword SM1A together with AM1 requests a calculation in aqueous solution by the AM1-SM1a method. The keyword SM1A functions analogously to SM1 with respect to energetics and output, with the exception that the accessible-surface-area terms are dependent not only on atomic number but also on chemical environment. When SM1A is specified the atom types must be provided to the program in the input file. They follow the connectivity information placed in a field added to the end of each atomic specification. No atom type entry need be made for dummy atoms as the program will not try to assign an atom type for them.

The allowed atom types in Version 4.1 of AMSOL are as follows:

  1. any carbon atom or attached hydrogen atom

  2. hydrogen atom attached to a nitrogen atom

  3. hydrogen atom attached to an oxygen atom

  4. hydrogen atom attached to a sulfur atom

  5. sp3 or amide nitrogen atom

  6. sp, sp2, or aromatic nitrogen atom

  7. sp3 oxygen atom

  8. sp2 oxygen atom (e.g., ketone, aldehyde, sulfoxide, nitro, etc.)

  9. fluorine atom

  10. sulfur atomm

  11. chlorine atom

  12. bromine atom

  13. iodine atom

  14. phosphorus atom or attached hydrogen

The output file will echo back the atom types it has assigned along with the geometric information, etc. If an atom is defined to have any number between the current highest defined type and 100, a factor of 0.00 will be employed for the surface area calculation.

While AM1-SM1a is more successful than AM1-SM1 in reproducing experimental free energies of solvation for neutral solutes, it suffers from the necessity of assigning explicit chemical environments. For cases where that is ambiguous, the user is left to his own intuition or else the AM1-SM2 or PM3-SM3 solvation models should be used. These models are very successful, nearly approaching the accuracy of AM1-SM1a, and they are applicable to ions and unusual bonding situations, whereas AM1-SM1a is not.





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