Hypertext Dalton 2.0 manual - Theoretical Chemistry, KTH

Chapter 13
Direct and parallel calculations
In this chapter we briefly discuss aspects connected to direct and parallel methods as implemented
in the dalton program.
13.1 Direct methods
Reference literature:
H. Ågren, O. Vahtras, H. Koch, P. Jørgensen, and T. Helgaker.
J. Chem. Phys., 98, 6471, (1993).
K. Ruud, D. Jonsson, P. Norman, H. Ågren, T. Saue, H. J. Aa. Jensen,
P. Dahle, and P. Dahle. J. Chem. Phys. 108, 7973 (1998).
The entire SCF and Kohn–Sham DFT part of the dalton code is direct, including
all derivative two-electron integrals, and all the way up to the cubic response function.
To perform a direct calculation, all that is required is to add the keyword .DIRECT in the
general input section, as indicated in the following input example for the calculation of
nuclear shieldings in a direct fashion:
**DALTON INPUT
.RUN PROPERTIES
.DIRECT
**WAVE FUNCTIONS
.HF
**PROPERTIES
.SHIELD
**END OF DALTON INPUT
By default the two-electron integrals will be screened [89], using an increasingly
tighter integral screening threshold during the SCF iterations. Thus, direct calculations
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