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A two electron-density-based DFT-like trans-correlated method for recovering dynamical correlation energy
Culberson, Lori Marie
Culberson, Lori Marie
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Text, Honors papers, Chemistry, Department of
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Abstract
We are interested in modeling large-scale biological systems, such as the binding
between tryptophan hydroxylase and aromatic ligands, a complex that is important in the
synthesis of serotonin. Due to the delocalization of electrons in these aromatic ligands,
dispersion forces are particularly important in these interactions, yet techniques for
calculating dispersion are limited. Current methods used to model such systems are either
inaccurate or time consuming: methods based on classical mechanics do not account for
correlation, and post-Hartree Fock correlation methods, like MP2, although accurate,
require insurmountable amounts of time when applied to large systems. A robust DFT
method which can accurately and efficiently describe dispersion is needed. Thus, we are
developing a novel density functional theory method, LMC DFT, designed to describe
dispersion forces, particularly those between proteins and ligands. Our method is based
on the Boys’ trans-correlated approach and uses both Hartee-Fock exchange and two
electron densities in the correlation energy functional. It is non-local and variational,
characteristics that contribute to its ability to accurately model dispersion. All integrals,
as well as the routine that solves the Shrödinger equation within each basis, are coded in
FORTRAN, and calculations are run on 64-bit-Opteron processors. We have tested this
method on two-, three-, and four-electron systems, benchmarking it on dispersion bound
H2—H and the helium dimer. Our results show that LMC DFT is capable of reproducing
a correction for dynamical correlation that is comparable to that of MP2 in a timely
fashion, and is promising for application to larger systems.