Molecular dynamics simulations for liquid methanol have been carried out in order to examine the hydrogen bond network pattern in the low-temperature regime. Those properties of methanol concerning hydrogen bond connectivity are compared with supercooled water. Methanol can be supercooled deep into the low-temperature region without any singular behavior, which is in sharp contrast to supercooled water. One-dimensional linear hydrogen-bonded chains with occasional branches are the predominant species from room temperature to 153 K. The number of hydrogen bonds per methanol molecule in the inherent structure remains constant over a wide range of temperature. Lowering the temperature simply reduces the number of branches, keeping the total number of hydrogen bonds constant. This is caused by a decrease of the methanol molecules hydrogen-bonded with one and three other molecules. It is found that the hydrogen bond strength does not vary with temperature. The potential energy of the inherent structure decreases with a temperature decrease, suggesting that methanol falls into a category of fragile liquid. The energy decrease is due mainly to an increase in density with declining temperature, which strengthens the Lennard-Jones interaction term. This feature is distinguished from water, where hydrogen bonds become gradually stronger with decreasing temperature in the normal supercooled state.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry