Address
Research Interests: My
main interest concerns the study of condensed matter physics and
statistical
mechanics, focussing my work in the liquid
phase. I spend most of my research
activity
working in theory and applications to the structure and dynamics of
simple
and complex liquids, with special attention paid to water,
alcohols and aqueous electrolyte
solutions. I have performed computer
simulations
with
several methods: molecular dynamics, Monte Carlo, EVB. In the last
years, I
have participated in studies of rare
events
and its applications to biological systems.The behavior of
liquid
and supercritical water under confinement
in carbon nanotubes
or near surfaces has been analyzed. Recently, I have started to
use and
develop mixed
quantum-classical methods
applied to computer simulations of liquids.
Selected topics:
A. Liquid water and aqueous
solutions
Liquid water at 298 K: A tetrahedral network of water molecules is the main structural trend, due to the existence of four hydrogen-bonds per molecule (on average). The lifetime of such hydrogen-bonds is around 1 ps. Hydrogen-bonding is the main responsible of the amazing properties of liquid water. This part of my research is carried out in collaboration with Joan Àngel Padró (University of Barcelona) and Elvira Guàrdia (UPC).
Structure of supercritical
water
at 723 K. Water beyond its critical point
(T > 647.13 K, d > 0.322 g/cm³, P > 220.55 bar) shows
surprising new
properties, like the capacity of mixing with oil. In supercritical
water
there is no longer distinction between the liquid and vapor phase. We
have
observed the breakdown of the tetrahedral structure and its
substitution
by cavities and water clusters. The lifetime of hydrogen-bonds is now
about
0.3-0.5 ps. This part of my research is carried out in collaboration
with
Elvira Guàrdia (UPC).
C. Rare events in chemical
physics
and biophysics
Lipid chain performing a flip-flop transition in a biological membrane. The study of rare events is a computational challenge due to the tiny amount of trajectories in phase space which lead to such phenomena, compared with the total amount of trajectories described by a microscopical system. A new technique named transition path sampling, which is able to analyze reactive trajectories in configurational space without preconceived information about potential energy surfaces or transition states of the system, has been recently developped by the research group of David Chandler in the University of California at Berkeley. We have employed that technique to study the transition state structure of NaCl dissociation in water and, more recently, flip-flop transitions of lipids in biomembranes. That reserach has been done in collaboration with David Chandler (University of California, Berkeley) concerning NaCl dissociation and also Félix S. Csajka (Max-Plank Institute for Colloids and Interfaces, Potsdam) about NaCl dissociation and lipid transitions.
D. Liquid and supercritical
water
under confinement
Liquid water at 298 K adsorbed in
a carbon nanotube of radius 40 nm. When
liquids are constrained inside solid devices, its behavior can suffer
dramatic
changes. In the case of water, confinement produces marked loss of
structural
order and modifications in its microscopic dynamics. We have simulated
several liquid and supercritical water samples when constrained by
rigid
and soft carbon nanotube walls. One of the most relevant cases is that
of quasi-one dimensional liquid
water, when liquid water is simply composed by
linear chains constrained inside a nanotube with a radius of
approximately 26 nm! The influence of the tubes is especially
relevant concerning hydrogen stretching vibrations and diffussive
behavior.
This research work is been produced in collaboration with M.C.Gordillo
(Pablo de Olavide University at Seville) and Elvira Guàrdia
(UPC).
The water-solid interface. As another example of confinement, we have simulated
liquid water imbedded in between two flat graphite layers. This is a
"classical" system in simulation studies which we will use to learn
further about modifications in the structure and dynamics of water under extreme confinement. In the
limit, we are able to speak about 2D
water.The influence of the tubes is especially
relevant concerning hydrogen stretching vibrations and diffussive
behavior.
This research work is been produced in collaboration with M.C.Gordillo
(Pablo de Olavide University at Seville), Gabor Nagy (Atomic Energy
Research Institute of the Hungarian Academy of Sciences) and Elvira Guàrdia (UPC)
Publication list:
Books:
A course in quantum field
theory
(in
catalan), J.Martí and J.Fernández. Publicacions
Promocions
Universitàries. Barcelona, 1993.
Articles:
Liquid water and aqueous solutions
Rare events in biochemical systems
Water
under
confinement (carbon nanotubes, near surfaces)
Teaching activity:
1. Physics for computer science students, Faculty of Computer Science, UPC, Barcelona.
2. Physical
foundations of technologies applied to computer science,
Faculty of Computer Science, UPC, Barcelona.