Applications of the orbital-free embedding formalism to study dynamics of molecules in condensed phase

• Research unit: COST
• Project number: C02.0087

Key words (English)

multi-scale modelling; condensed phase; electronic structure; first principles; dynamics

Research programs (English)

COST-Action D26 - Integrative Computational Chemistry

Short description (English)

The project concerns the computer simulations of molecules in condensed phase (on surfaces, in porous solids, in liquids, inside nanocapsules, etc.) at quantum mechanical level. Its novelty of the lies in the use of a new method, developed in our group, to couple different parts of a larger systems described at different levels by means of the universal orbital-free embedding potential. Such a strategy results in significant potential savings in the computer time compared to such alternative strategies in which both the molecule under investigation and its chemical environment are described using the same (quantum mechanical) level of approximation.

Partners and International Organizations (English)

AT, BE, BG, CH, DE, ES, FI, FR, GR, HR, HU, IL, IT, LT, MK, NL, NO, PL, SE, SK, UK

Abstract (English)

Abstract 2004 In May 2002, we started working on development of a new computer implementation of the orbital-free embedding formalism better suitted then the previous one, which was developed mainly to study methodology related issues, for various types of applications in computer simulations of complex materials. One of such applications planned using the new implementation concerns the dynamics of embedded molecules- the primary objective of this project. The progress concerning some numerical aspects of this new implementation was reported in the recent publication (Dulak and Wesolowski, Intl. J. Quant. Chem. (2005) in Press). However, no funds from OFES were used to support these works in the period from 1May 2003 to 1May 2004. Abstract 2005 The objectives of this proposal involve three types of work: A) Development and testing of the software, B) Verification of the used approximations to the functionals and electron densities in pilot studies for model systems, C) Large scale computer simulations and analysis. Work on A) and B) involves one PHD student (not financed by OFES) and one post-doctoral researcher (since Sept 2004). This resulted in the possibility to start run large-scale simulations aimed at studying the statistical behaviour of the water molecule in a porous solid (EMERALD). This system was chosen as the first application of the developed simulation technique. Simulations and analysis are in progress. The main achievements in the reporting period include: I) Development of the numerical implementation of one-electron equations for embedded orbitals introduced by Wesolowski and Warshel in 1993 suited for their application in multi-scale type of nu-merical simulations (orbital-free embedding). The key elements of this numerical implementations include: a) the analytic evaluation of energy gradients, b) the efficient numerical integration technique based on adaptive grid, c) an efficient algorithm to perform energy minimisation based on coupled constrained optimisations of electron density and nuclear coordinates. II) Determination of the domain of applicability of the approximated density functionals used in the one-electron equations for embedded orbitals: a) For interaction energies and intermolecular forces in hydrogen bonded complexes, the non-empirical functionals based on local density approximations lead to the results of the quality compa-rable with that of high-level wave-function based methods. b) For the electronic structure (orbital levels, response properties), orbital-free embedding formalism is very adequate for cases in which the overlap between the electron density of the investigated embedded system and the electron density of its environment is weak (hydrogen or ionic bonds, for instance). Cases involving covalent bonding cannot, however, be treated using approximations de-veloped so far. III) Performing the first large-scale numerical simulations of molecules, in which one-electron equa-tionds for embedded orbitals were used to obtain the the electronic properties (excitation spectra and hyperfine structure) of solvated molecules. IV) Formal unification of the orbital-free embeding formalism with linear-response density functional theory framework to obtain excitation energies.

References in databases (English)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C02.0087