RESEARCH
EXPERTISE
• Ground state properties of solids and molecules: equilibrium
geometry and electronic structure in the DFT framework with
plane wave and localized basis sets. Use of public codes:
Abinit, PWscf, Octopus, Gaussian, NWChem
• Electronic band structure calculations of
bulk and quasione dimensional systems (polymers) within DFT
and GW methods. Use of public codes: Abinit, PWscf, Yambo.
• Optical properties of nanostructures within
Time Dependent Density Functional Theory in time and frequency
domain and with the inclusion of excitonic effects. Use of
public codes: Yambo,
Octopus
• Quantum Montecarlo Methods for fermions with
variational and diffusion algorithms. (inhouse code)
CURRENT SCIENTIFIC ACTIVITY AND INTEREST
My main activities are concerned with the theoretical and
computational study of electronic and optical properties of
low dimensional systems with abinitio techniques. The main
research topics are:
a) Optical properties of biological photoreceptors.
My activity in this field is devoted to the study of biophysical
processes in the microscopic description of the photoresponse
of biomolecules. Within the Time Dependent Density Functional
Theory framework we have calculated the optical response of
the Green Fluorescent Protein (GFP), of the DNA bases and
their assemblies, and of modified aromaticexpanded DNA bases.
The computed absorption spectrum of GFP is in close agreement
with the measured spectrum and gives support to the suggested
model of the GFP photophysics that contains two thermodynamically
stable neutral and anionic configurations of the cromophore.
With the same theoretical technique we have studied the absorption
spectra of isolated DNA bases. The results are in agreement
with experiment and previous calculations. Then I have inspected
the impact on the optical properties of the Hbonding when
the bases are paired in theWatsonCrick configuration, and
of the stacking interactions between base pairs. Currently
I am studying the optical properties of the bases and assemblies
of bases of a modified aromaticexpanded DNA (xDNA), a modified
genetic system that is a good candidate for molecular electronic
due to the enhanced stacking interactions between planes of
base pairs. Moreover, I am codeveloping a theory that permits
the calculation of circular dichroism in the TDDFT framework.
This research activity has started during my Phd studies and
is now going on during my Postdoc, in collaboration with
Dr. Rosa Di Felice, Prof. Angel
Rubio and Prof. Miguel Marques.
b) Electronic properties of G4DNA with sequence
alternations explored for devices. My research activity in
this field is devoted to the theoretical study of DNAderivatives
in order to implement DNAbased electrical devices. The electrical
conductivity of nativeDNA is still disputable, and a possible
alternative to go beyond the limits of nativeDNA is to design
and realize modifications of the DNA structure, such as an
alteration of the helical motif from the doublestranded helix
to a quadruple helix. It has been demonstrated that the electronic
structure of a quadruple helix made of guanines reveals better
channels for charge motion than in native DNA. I am now investigating
if an alternation of the sequence, obtained by inserting adenine
tetrads into the stack of guanine tetrads , may interrupt
the electronic channel and behave as an electric nonlinear
element.
This work is done in collaboration with Dr.
Rosa Di Felice. In addition, I am investigating the electronic
coupling matrix elements, between adjacent base pairs in xDNA
(see above).
c) Optical properties of molecular chains
and quasione dimensional systems. One dimensional molecular
chains (i.e. polymers) are paradigmatic systems where independent
particle approximations fail to furnish a good description
of the optical properties, or the static polarizability. During
my PhD I have studied such systems showing that the spatial
confinement plays an important role in enhancing the short
distance interactions. Due to this fact an appropriate description
of the optical properties of such systems, as a function of
the chain length, can be obtained considering the electronhole
attraction in a manybody approach, based on the Green’s function
method (Bethe Salpeter equation). Moreover I have shown that
the saturation of the polarizability is driven by exciton
localization and that the TDDFT approach can be also used
when sophisticated kernels extracted from the manybody perturbation
theory are used.
This work has been done in collaboration with Dr. Andrea
Marini and Prof. Angel Rubio.
Actually I am
studying, within the Bethe Salpeter framework the excitonic
effects present in the absorption spectrum of graphene nanoribbons,
a novel quasionedimensional carbonbased systems, suitable
for future nanoscale optoelectronics applications. This work
is done in collaboration with Deborah
Prezzi, Dr. Alice Ruini and Prof.
Elisa Molinari.
PAST RESEARCH EXPERIENCE
During my research period at the University of Romw ”La Sapienza”
my research activity has been focused on the study of the
magnetic phase of the 2D electron gas near freezing. This
work has be done in collaboration with Dr. Saverio Moroni,
and Prof. Gaetano Senatore. We performed variational and diffusion
Monte Carlo calculation in the fixednode approximation. We
found the evidence for a polarization transition at densities
achievable nowadays in 2dimensional hole gases in semiconductor
heterostructures. The spin susceptibility of the unpolarized
phase at themagnetic transition is approximately 30 times
the Pauli susceptibility. Moreover, at variance with the 3D
case we found no evidence for the stability of a partially
polarized phase.
CODE DEVELOPMENT
Since 2002 I am involved in the developers team of the high
performance computing parallel code Yambo: (www.yambocode.org).
Yambo is a FORTRAN/C code for ManyBody calculations
in solid state physics. It relies on the KohnSham wavefunctions
generated by several DFT public codes as Abinit (www.abinit.org)
and PWscf (www.pwscf.org).
It uses plane wave basis sets, and permits the calculation
of photoemission spectra within the GW approximation and
optical properties via Time Dependent Density Functional Theory
and it includes excitonic effects via the Bethe Salpeter equation.
My main contributions in the code development have been: i)
the development and implementation of a technique to permit
the treatment of finite and quasione dimensional systemswithin
the supercell approximation, ii) the implementation of the
BetheSalpeter equation beyond the TammDancoff approximation
and iii) the development of the excitonic wavefunctions drawing
tools.
LIST OF PUBLICATIONS
INTERNATIONAL JOURNALS
 A. Calzolari, D. Varsano, A. Ruini, A. Catellani,
R. TelVered, H.B. Yildiz, O. Ovits, Oded; I. Willner, "Optoelectronic
properties of natural cyanin dyes", J. Phys. Chem. A 113 8801
(2009).
 L. Nielsen, A. Holm, D. Varsano, U. Kadhane, S.
Hoffmann, R Di Felice, A. Rubio and S. Nielsen "Fingerprints
of bonding motifs in DNA duplexes of adenine and thymine
revealed from circular dichroism: synchrotron radiation
experiments and TDDFT calculations", J. Phys. Chem B
113, 9614 (2009).
 A. Migliore, S. Corni, D. Varsano, M. L. Klein,
and R. Di Felice "Firstprinciples effective electronic
couplings for hole transfer in natural and sizeexpanded
DNA", J. Phys. Chem. B 113, 9402 (2009).
 D. Varsano, L. A. EspinosaLeal, X. Andrade, M.
A. L. Marques, R. Di Felice, and A. Rubio, "A gauge invariant
method for molecular chiroptical properties in TDDFT", Phys.
Chem. Chem. Phys. 11, 4481 (2009).
 N. Spallanzani, C. A. Rozzi, D. Varsano, T. Baruah,
M. R. Pederson,F. Manghi, and A. Rubio, "Photoexcitation
of a lightharvesting supramolecular triad: a TimeDependent
DFT study", J. Phys. Chem. B 113, 5345 (2009).
 A. Marini, C. Hogan, M. Gruning and D. Varsano,
"yambo: an abinitio tool for excited state calculations"
Comp. Phys. Comm., in press (2009).
 A. Castro, M. A. L. Marques, D. Varsano, F. Sottile
and A. Rubio "The challenge of predicting optical properties
of biomolecules: What can we learn from timedependent densityfunctional
theory", Compte Rendus Physique, in press (2008).
 D. Varsano, A. Marini and A. Rubio, "Optical
saturation driven by exciton confinement in molecularchains:
A timedependent densityfunctional theory approach",
Phys. Rev. Lett. 101, 133002 (2008).
 D. Prezzi, D. Varsano, A. Ruini, A. Marini, E.
Molinari, "Optical properties of graphene nanoribbons:
The role of manybody effects" Phys. Rev. B 77,
R041404 (2008).
 D. Prezzi, D. Varsano, A. Ruini, A. Marini, E.
Molinari, "Optical properties of onedimensional graphene
polymers: the case of polyphenanthrene", phys. stat.
sol. (b) 244, 4124 (2007).
 D. Varsano, A. Garbesi and R. Di Felice, "Ab
initio optical absorption spectra of sizeexpanded xDNA
base assemblies", J. Phys. Chem. B 111,
14012 (2007).
 C. A. Rozzi, D. Varsano, A. Marini, A. Rubio and
E.K.U Gross, "An exact Coulomb cutoff technique for
supercell calculations" Phys. Rev. B 73,
205119 (2006).
 D. Varsano, R. Di Felice, M.A.L Marques and A.
Rubio, " A TDDFT study of excited states of DNA bases
and their assemblies:, J. Phys. Chem. B 110,
7129 (2006).
 D. Varsano, M.A.L. Marques and A. Rubio, "Time
and Energy resolved two photon photoemission of the Cu(100)
and Cu(111) metal surfaces", Computational Material
Science 30, 110 (2004).
 M.A.L. Marques, X. Lopez, D.Varsano, A. Castro
and A. Rubio, "Time Dependent Density Functional approach
for biological chromophore: The case of the Green Fluorescent
Protein", Phys. Rev. Lett. 90, 258101
(2003).
 D. Varsano, S. Moroni and G. Senatore, "Spinpolarization
transition in the twodimensional electron gas", Europhys.
Lett. 53 348 (2001).
 G. Senatore, S. Moroni and D. Varsano, "Spin
effects in the 2D electron gas", Sol. St. Commun.
119, 333 (2001).
 G. Senatore, S. Moroni and D. Varsano, "Spontaneous
magnetization of the 2D electron gas", Computer
Phys. Commun. 142, 406 (2001).
CHAPTER OF BOOKS
 R. Di Felice, A. Calzolari, D. Varsano and A.
Rubio, "Electronic structure calculations for nanomolecular
systems in Introducing Molecular Electronics, edited
by G.Cuniberti. K. Richter and G. Fargad. Lecture Notes
in Physics Vol.680 (Springer, Berlin, 2005). Proceedings.
 A. Castro, M.A.L Marques, X. Lopez, D. Varsano
and A. Rubio, "Excited states properties of nanostructures
and biomolecules through time dependent density functional
theory", Proceedings of the 3rd International Conference
”ComputationalModeling and Simulation of Materials&Special
Symposium” Modeling and SimulatingMaterialsNanoworld”, Acireale,
Italy, 2004.
POPULAR SCIENCE ARTICLES
 D. Varsano, "Role of Hbonding and ¼ stacking
in the optical absorption of DNA nucleobase assemblies",
Bulletin of the Network of Excellence Nanoquanta,
28 October 2005.
 M.A.L Marques, X. Lopez, D. Varsano, A. Castro
and A. Rubio, "Understanding biological photoreceptors",
Donostia International Physics Center Highlight,
2003.
 A. Rubio, D. Varsano, M. Marques, A. Castro, J.
Serrano, M. J. Lopez, V. M. Silkin and P.M. Echenique, "Simulaci´o
de les propietats electr´oniques i estructurals de nanotubs
i nanoestructures i les seves aplicacions tecnol´ogiques",
TERAFLOP Revista del centre de supercomutaci ´o de
Catalunya 61, 21, (2001).
