First-principles calculation of thermodynamic stability of acids and bases under pH environment: A microscopic pH theory

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Despite being one of the most important thermodynamic variables, pH has yet to be incorporated into first-principles thermodynamics to calculate stability of acidic and basic solutes in aqueous solutions. By treating the solutes as defects in homogeneous liquids, we formulate a first-principles approach to calculate their formation energies under proton chemical potential, or pH, based on explicit molecular dynamics. The method draws analogy to first-principle calculations of defect formation energies under electron chemical potential, or Fermi energy, in semiconductors. From this, we propose a simple pictorial representation of the general theory of acid-base chemistry. By performing first-principles molecular dynamics of liquid water models with solutes, we apply the formulation to calculate formation energies of various neutral and charged solutes such as H+, OH-, NH3, NH4+, HCOOH, and HCOO-in water. The deduced auto-dissociation constant of water and the difference in the pKa values of NH3 and HCOOH show good agreement with known experimental values. Our first-principles approach can be further extended and applied to other bio- and electro-chemical molecules such as amino acids and redox reaction couples that could exist in aqueous environments to understand their thermodynamic stability. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3700442]
Publisher
AMER INST PHYSICS
Issue Date
2012-04
Language
English
Article Type
Article
Keywords

DENSITY-FUNCTIONAL THEORY; WATER; DYNAMICS; PK(A); GAAS; SEMICONDUCTORS; HYDROLYSIS; POTENTIALS; ENERGETICS; SOLVATION

Citation

JOURNAL OF CHEMICAL PHYSICS, v.136, no.13

ISSN
0021-9606
DOI
10.1063/1.3700442
URI
http://hdl.handle.net/10203/101735
Appears in Collection
NT-Journal Papers(저널논문)
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