The Initial Guess Data File

The file default.atomig contains the results of Hartree-Fock calculations on atoms for various basis sets. By default, the initial guess is constructed from orbitals in this file. When the basis set to be used for the calculation is one of those listed below (or any variant of these sets involving polarization or diffusion functions, such as 6‑31G*), the initial guess is formed from orbitals obtained from atomic calculations in the listed basis set.

Therefore, if you change the .basis file, you need to change the .atomig file correspondingly, and vice versa.

For other basis sets, the wave functions used to construct the initial guess are obtained by projecting the appropriate atomic orbitals in default.atomig onto the basis set actually being used for the molecular calculation. The 6‑31G wave function is used whenever possible; when a 6‑31G atomic wave function is not listed for a particular atom, the MSV wave function is used for that atom. For atoms beyond Xe in calculations using the LAV1S basis set, the LAV2P atomic results are used. It is important to add an initial guess if you add an ECP basis set, as projection onto another guess is likely to give bad results.

The overall structure of the initial guess data file is as follows. As in the default.basis file, the basis sets are listed in turn, and for each basis, the information for each atom is listed.

BASIS basis-name-listatom-blockatom-block
...
atom-block
 
BASIS basis-name-listatom-blockatom-block
...
atom-block
...

Each basis set section begins with a blank line The basis sets for this section are defined with on the BASIS line, where the names of all basis sets to which the following atomic sections apply are listed, separated by a space and/or comma. The basis set names are listed in Basis Sets.

Each atom block in the basis set section has the following structure:

atom-symbol comment
num-basis-functions num-ECP-core-electrons
orbital-index fractional-occupation orbital-energy
coefficient-list
orbital-index fractional-occupation orbital-energy
coefficient-list
...
****

The first line lists the atomic symbol for the atom, followed by information which is simply a comment and is not read in. The second line gives the number of basis functions for that atom and basis set, as listed in the default.basis file, followed by the number of electrons for that atom that are included in an effective core (0 for the basis sets listed in Table 1 in Basis Sets).

The orbitals for the atom are specified next. The first line in an orbital specification gives the orbital index (1 for the first orbital, 2 for the second, and so on), the fractional orbital occupation (1.0 if the orbital is fully occupied, 0.5 for a half-filled shell, and so on), and the orbital energy in hartrees. The orbitals should be listed in ascending periodic table order, with the fully occupied orbitals first. The coefficients of each basis function for that orbital follow, in the order in which the basis functions are given in the default.basis file. The basis functions are taken to be normalized to 1 radially. The coefficients must be given for the components of each shell: for example, there must be three coefficients for a p shell, in the order p_x, p_y, p_z. The shells are in Cartesian representation, so for a d shell you must give the coefficients for the six Cartesian components in the order d_xy, d_xz, d_yz, d_xx, d_yy, d_zz, and for an f shell in the order f(x³), f(y³), f(z³), f(xy²), f(x²y), f(x²z), f(xz²), f(yz²), f(y²z), f(xyz). You can spread the coefficients over multiple lines. You can also include low-lying virtual orbitals with an occupation number of 0.0, such as the 2p orbital for Li or Be. The atom block is terminated by four stars.

You can create your own initial guess file using the format described above. To use it in a Jaguar calculation, you must add a line in the form

ATOMIGFILE: filename

to the input file for the job. The file name must not include a path, and the file must be in the same directory as your input file. The file name is arbitrary, but you might want to use the suffix .atomig to mark it as an initial guess file.

If you need to generate the atomic wave functions for your basis set to add to the default initial guess file, default.atomig, or to your own initial guess file, you must run a series of atomic calculations, one for each element covered by the basis set, using the atguess=1 setting in the gen section. Set the basis keyword appropriately, but do not include any polarization functions, as these are not occupied for the neutral atom. Do not set any other keywords. There is no need to set the multiplicity because high spin is assumed, and all valence orbitals are equally (and usually fractionally) occupied. After the job runs, copy the jobname.ig file to the appropriate basis set entry in the default.atomig file or your own initial guess file.