複製交換メタダイナミクスによるクラスターの有限温度特性:水非亜米
Yingteng Zhai1, Alessandro Laio, Erio Tosatti
1Key Laboratory for Computational Physical Sciences (MOE), Fudan University, Shanghai, China.
Journal of the American Chemical Society
|February 5, 2011
まとめ
ナノクラスターの熱的性質を計算するための新しい方法を紹介します. このアプローチは,すべてのエントロピー源を正確に含み,水の非アメルの温度に対する驚くべき自由エネルギー変化を明らかにします.
科学分野:
- 計算化学はコンピュータ化学である.
- 統計力学 統計力学とは
- マテリアルサイエンス 材料科学
背景:
- ナノクラスターの熱的性質の正確な計算は,それらの振る舞いを理解するために重要です.
- 伝統的な方法は,しばしば重要なエントロピーの貢献,特に構成エントロピーを無視します.
- ノーアマーと同様に,水のナノクラスターは,様々な科学分野に関連した複雑な構造と物理学を示しています.
研究 の 目的:
- クラシックなナノクラスターの熱的性質の正確な決定のための新しい計算アプローチを導入する.
- 振動的,回転的,および構成的エントロピーを含むエントロピーのすべての源を完全に組み込む.
- モデルのシステムとして,水非アマー (H2O) 9 を使用して,方法の能力を実証します.
主な方法:
- レプリカ交換メタダイナミクスを利用し,強化されたサンプリング技術である.
- クラスター構造の均衡占有率をサンプリングすることによって,クラスター構造の真の自由エネルギーを直接計算します.
- シミュレーションでは,TIP4Pの水モデルを使用しています.
主要な成果:
- この方法は,すべてのエントロピーの源を含むことで熱的性質をうまく計算します.
- 水のノンアマー (H2O) 9の場合は,第2の最も関連する構造は,第1の構造よりも高い構成エントロピーを示します.
- 最初の2つの関連する水非アマー構造体の自由エネルギーは,温度が上昇するにつれて交差することが判明しました.
結論:
- 開発された方法は,ナノクラスターの正確な熱特性計算を提供します.
- 構成エントロピーは,クラスター構造の相対的な安定性において重要な役割を果たします.
- この発見は,ナノクラスター熱力学の包括的な理解のために,すべてのエントロピー源を考慮することの重要性を強調しています.
関連する概念動画
Phase Transitions: Melting and Freezing
Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
States of Water
Water exists in any one of the three classical states: solid (ice), liquid (water), and gas (steam or water vapor). The state of water depends on i) the intermolecular forces that draw molecules together and ii) the kinetic energy that leads to movements that pull them apart.
Water freezes when the intermolecular forces are greater than the kinetic energy. Unlike most other substances, water is less dense in its solid state than in its liquid state. This is because each water molecule can form...
Water freezes when the intermolecular forces are greater than the kinetic energy. Unlike most other substances, water is less dense in its solid state than in its liquid state. This is because each water molecule can form...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
Heating and Cooling Curves
When a substance—isolated from its environment—is subjected to heat changes, corresponding changes in temperature and phase of the substance is observed; this is graphically represented by heating and cooling curves.
For instance, the addition of heat raises the temperature of a solid; the amount of heat absorbed depends on the heat capacity of the solid (q = mcsolidΔT). According to thermochemistry, the relation between the amount of heat absorbed or released by a substance, q, and its...
For instance, the addition of heat raises the temperature of a solid; the amount of heat absorbed depends on the heat capacity of the solid (q = mcsolidΔT). According to thermochemistry, the relation between the amount of heat absorbed or released by a substance, q, and its...
Noncovalent Attractions in Biomolecules
Noncovalent attractions are associations within and between molecules that influence the shape and structural stability of complexes. These interactions differ from covalent bonding in that they do not involve sharing of electrons.
Four types of noncovalent interactions are hydrogen bonds, van der Waals forces, ionic bonds, and hydrophobic interactions.
Hydrogen bonding results from the electrostatic attraction of a hydrogen atom covalently bonded to a strong-electronegative atom like oxygen,...
Four types of noncovalent interactions are hydrogen bonds, van der Waals forces, ionic bonds, and hydrophobic interactions.
Hydrogen bonding results from the electrostatic attraction of a hydrogen atom covalently bonded to a strong-electronegative atom like oxygen,...
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...


