Multilevel X-Pol: A fragment-based method with mixed quantum mechanical representations of different fragments

Yingjie Wang, Carlos P. Sosa, Alessandro Cembran, Donald G Truhlar, Jiali Gao

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


The explicit polarization (X-Pol) method is a fragment-based quantum mechanical model, in which a macromolecular system or other large or complex system in solution is partitioned into monomeric fragments. The present study extends the original X-Pol method, where all fragments are treated using the same electronic structure theory, to multilevel representations, called multilevel X-Pol, in which different electronic structure methods are used to describe different fragments. The multilevel X-Pol method has been implemented into a locally modified version of Gaussian 09. A key ingredient that is used to couple interfragment electrostatic interactions at different levels of theory is the use of the response density for the post-self-consistent-field energy. (The response density is also called the generalized density.) The method is useful for treating fragments in a small region of the system such as a solute molecule or the substrate and amino acids in the active site of an enzyme with a high-level theory, and the fragments in the rest of the system by a lower-level and computationally more efficient method. Multilevel X-Pol is illustrated here by applications to hydrogen bonding complexes in which one fragment is treated with the hybrid M06 density functional, Møller - Plesset perturbation theory, or coupled cluster theory, and the other fragments are treated by Hartree - Fock theory or the B3LYP or M06 hybrid density functionals.

Original languageEnglish (US)
Pages (from-to)6781-6788
Number of pages8
JournalJournal of Physical Chemistry B
Issue number23
StatePublished - Jun 14 2012


Dive into the research topics of 'Multilevel X-Pol: A fragment-based method with mixed quantum mechanical representations of different fragments'. Together they form a unique fingerprint.

Cite this