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##### Publikationer (10 of 15) Visa alla publikationer
Thiyam, P. (2018). A study of finite-size, non-perturbative and anisotropic effects on the Lifshitz-van der Waals forces and torque with material dielectric responses from first-principles calculations. (Doctoral dissertation). KTH Royal Institute of Technology
Öppna denna publikation i ny flik eller fönster >>A study of finite-size, non-perturbative and anisotropic effects on the Lifshitz-van der Waals forces and torque with material dielectric responses from first-principles calculations
2018 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
##### Abstract [en]

The van der Waals and the Casimir-Lifshitz forces are forces of attraction that exist between neutral polarizable bodies due to quantum fluctuations. They can be repulsive depending on the material properties and the geometry of the system. Since they are pervasive in nature, they encompass a great deal of relevance in the study of interaction between bodies in several different scenarios and background geometrical settings.

This doctoral thesis first addresses the important aspects of finite-size and the non-perturbative effects of the van der Waals interactions between two atoms or molecules. Going beyond the usual assumption of atoms and molecules as point particles and adopting a description of finite size, the divergence inherent in such interaction energies in the limit of zero separation distance between the two interacting atoms or molecules is removed. The attainment of finite interaction energy at such close separation distance facilitates the estimation of van der Waals force contribution to the binding energy of the molecules, and towards surfaces. This is particularly important for noble atoms. The interaction between a pair of helium (He) atoms and krypton (Kr) atoms, and between a pair of methane (CH$_4$) molecules considering its environmental relevance, is investigated in detail. The application of finite size further leads to finite self energies of the atoms. The full expression of the interaction energy, as is discussed in detail in this thesis, typically contains a logarithmic factor of the form $\ln(1 \pm x)$. Formerly, in evaluating the interaction energies, this factor is customarily series-expanded and truncated in the leading order with certain assumptions. This thesis explores the effect of using the full expression, which is referred herein as the non-perturbative (or, the non-expanded) theory, analytically wherever possible as well as numerically. The combined application of the finite-size theory and the non-perturbative theory results in as much as 100\,\% correction in the self energy of atoms in vacuum. This may give rise to significant physical consequences, for example, in the permeabilities of atoms across dielectric membranes.

The thesis next addresses the aspect of anisotropy in the Casimir-Polder interaction between a completely polarizable molecule and a dielectric slab polarizable in the normal direction. The formalism is applied to the study of preferential adsorption in the specific case of carbon dioxide (CO$_2$) and methane (CH$_4$) molecules interacting with amorphous silica slabs and thin gold films. Owing to its greater polarizability, the linearly polarizable CO$_2$ molecule is found to attract more towards the surfaces than the isotropically polarizable CH$_4$ molecule. In addition, the stable orientation of the CO$_2$ molecule with respect to the surface is determined to be the one in which the long, linear axis of the molecule is perpendicular to the surface. Further, the feature of Casimir torque which is a consequence of anisotropy in the interacting dielectric slabs is explored in the case of biaxial materials, in particular the bulk black phosphorus and its novel 2D counterpart phosphorene. The torque between a pair of phosphorus slabs, one face rotated with respect to the other, is observed to change sign at a particular separation distance which is determined by the crossing frequency of its planar dielectric components. This distance-dependent reversal of the sign of torque has never been observed before. The observation is verified with several other biaxial materials. This finding will help assist in the experimental detection of the Casimir torque, and can potentially be exploited in the future for designing nanodevices.

Another remarkable effect that is uncovered is the submersion of ice microcrystals under water governed by the balance of repulsive Lifshitz force from the vapor-water interface and the buoyant force of water. The repulsive effect is found to be enhanced by the presence of salt ions in the system. An exclusion zone ranging from 2 nm to 1 ${\mu}$m devoid of small ice particles is formed below the water surface. As the ice sphere grows in size, the buoyant force overcomes the Lifshitz force, and the ice sphere starts to float with a fraction of its volume above the water surface in accordance with the classical Archimedes principle. The combined impact of Lifshitz forces and double-layer interactions is further investigated in ice-water-CO$_2$ and vapor-water-CO$_2$ systems  employing different models of effective polarizability for ions, {\it viz.} the hardsphere model and Onsager's model. The CO$_2$ bubble is found to be repelled by the vapor-water interface and attracted towards the ice-water interface. The equilibrium thin film of water formed between vapor and ice surfaces varies in thickness depending on the model of effective polarizability and the type of salt present in the system. Further studies of the interaction energy in geometries comprising two molecules near an interface and molecule in a three-layer geometry are conducted which may be relevant for potential energy storage applications. The density functional theory (DFT) is employed to generate the frequency-dependent dielectric functions required for Lifshitz energy and force calculations.

Summing up, in the numerous contexts outlined above, the importance of the van der Waals and Lifshitz forces has been demonstrated. The studies in this thesis enable significant predictions related to these forces which may be verifiable by experiments.

##### Ort, förlag, år, upplaga, sidor
KTH Royal Institute of Technology, 2018. s. 112
##### Serie
TRITA-ITM-AVL ; 2018:16
##### Nyckelord
Lifshitz-van der Waals forces, Casimir torque, optical calculations with density functional theory, phosphorus, phosphorene
##### Nationell ämneskategori
Annan materialteknik
##### Identifikatorer
urn:nbn:se:kth:diva-227041 (URN)978-91-7729-789-5 (ISBN)
##### Disputation
2018-05-25, D3, Lindstedtsvägen 5, Stockholm, 13:15 (Engelska)
##### Handledare
Thiyam, P. (2018). Distance-Dependent Sign Reversal in the Casimir-Lifshitz Torque [Letter to the editor]. Physical Review Letters, 120(131601)
Öppna denna publikation i ny flik eller fönster >>Distance-Dependent Sign Reversal in the Casimir-Lifshitz Torque
2018 (Engelska)Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, nr 131601Artikel i tidskrift, Letter (Refereegranskat) Published
Naturvetenskap
##### Identifikatorer
urn:nbn:se:kth:diva-226959 (URN)10.1103/PhysRevLett.120.131601 (DOI)000428243400001 ()2-s2.0-85044837771 (Scopus ID)
##### Anmärkning

QC 20180515

Thiyam, P., Fiedler, J., Buhmann, S. Y., Persson, C., Brevik, I., Bostrom, M. & Parsons, D. F. (2018). Ice Particles Sink below the Water Surface Due to a Balance of Salt, van der Waals, and Buoyancy Forces. The Journal of Physical Chemistry C, 122(27), 15311-15317
Öppna denna publikation i ny flik eller fönster >>Ice Particles Sink below the Water Surface Due to a Balance of Salt, van der Waals, and Buoyancy Forces
2018 (Engelska)Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 27, s. 15311-15317Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

According to the classical Archimedes' principle, ice floats in water and has a fraction of its volume above the water surface. However, for very small ice particles, other competing forces such as van der Waals forces due to fluctuating charge distributions and ionic forces due to salt ions and charge on the ice surface also contribute to the force balance. The latter crucially depends on both the pH of the water and the salt concentration. We show that a bulge in the air-water interface due to interaction of surface tension with the rising ice particle becomes significant when the particle radius is greater than 50-100 mu m. The role of these forces in governing the initial stages of ice condensation has never been considered. Here, we show that small ice particles can only form below an exclusion zone, from 2 nm (in high salt concentrations) up to 1 mu m (in pure water at pH 7) thick, under the water surface. This distance is defined by an equilibrium of upward buoyancy forces and repulsive van der Waals forces. Ionic forces due to salt and ice surface charge push this zone further down. Only after growing to a radius larger than 10 pm, will the ice particles eventually float toward the water surface in agreement with the simple intuition based on Archimedes' principle. Our result is the first prediction of observable repulsive van der Waals forces between ice particles and the water surface outside a laboratory setting. We posit that it has consequences on the biology of ice water as we predict an exclusion zone free of ice particles near the water surface which is sufficient to support the presence of bacteria.

##### Ort, förlag, år, upplaga, sidor
American Chemical Society (ACS), 2018
Fysikalisk kemi
##### Identifikatorer
urn:nbn:se:kth:diva-232902 (URN)10.1021/acs.jpcc.8b02351 (DOI)000439003600030 ()2-s2.0-85048664682 (Scopus ID)
##### Anmärkning

QC 20180808

Fiedler, J., Thiyam, P., Kurumbail, A., Burger, F. A., Walter, M., Persson, C., . . . Buhmann, S. Y. (2017). Effective Polarizability Models. Journal of Physical Chemistry A, 121(51), 9742-9751
Öppna denna publikation i ny flik eller fönster >>Effective Polarizability Models
2017 (Engelska)Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 121, nr 51, s. 9742-9751Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Theories for the effective polarizability of a small particle in a medium are presented using different levels of approximation: we consider the virtual cavity, real cavity, and the hard-sphere models as well as a continuous interpolation of the latter two. We present the respective hard-sphere and-cavity radii as obtained from density-functional simulations as well as the resulting effective polarizabilities at discrete Matsubara frequencies. This enables us to account for macroscopic media in van der Waals interactions between molecules in water and their Casimir-Polder interaction with an interface.

##### Ort, förlag, år, upplaga, sidor
American Chemical Society (ACS), 2017
Fysikalisk kemi
##### Identifikatorer
urn:nbn:se:kth:diva-221368 (URN)10.1021/acs.jpca.7b10159 (DOI)000419263900010 ()29185741 (PubMedID)2-s2.0-85038816623 (Scopus ID)
##### Anmärkning

QC 20180117

Priyadarshini, T. (2016). A study of finite-size and non-perturbative effects on the van der Waals and the Casimir-Polder forces. (Licentiate dissertation). Stockholm: KTH Royal Institute of Technology
Öppna denna publikation i ny flik eller fönster >>A study of finite-size and non-perturbative effects on the van der Waals and the Casimir-Polder forces
2016 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
##### Abstract [en]

This licentiate thesis addresses two important aspects of the van der Waals and the Casimir-Polder ground-state and excited-state (resonance) interactions between two atoms or molecules. The first is the finite-size effect and the second is the non-perturbative effect. Going beyond the usual assumption of atoms and molecules as point particles and adopting a description of finite size, the divergence inherent in such interaction energies in the limit of zero separation distance between the two interacting atoms or molecules is removed. The attainment of finite interaction energy at such close separation distance facilitates the estimation of van der Waals force contribution to the binding energy of the molecules, and towards surfaces. This is particularly important for noble atoms. We investigate in detail for a pair of helium (He) atoms and krypton (Kr) atoms, and for a pair of methane (CH4) molecules considering its environmental importance. The application of finite size further leads to finite self energies of the atoms. The expression of the interaction energy, as is discussed in detail in this thesis, typically contains a logarithmic factor of the form ln(1-x). Formerly, in evaluating the interaction energies, this factor is customarily series-expanded and truncated in the leading order with certain assumptions. This thesis explores the effect of using the full expression, which we refer to as the non-perturbative (or, the non-expanded) theory, analytically wherever possible as well as numerically. The combined application of the finite-size theory and the non-perturbative theory results in as much as 100% correction in the self energy of atoms in vacuum. This may give rise to significant physical consequences, for example, in the permeabilities of atoms across dielectric membranes. The non-perturbative theory, in addition, exhibits interesting behaviour in the retarded resonance interaction.

##### Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2016. s. 58
##### Nyckelord
finite-size effects, non-perturbative theory, van der Waals and Casimir Polder forces
Fysik
##### Forskningsämne
Teknisk materialvetenskap
##### Identifikatorer
urn:nbn:se:kth:diva-186225 (URN)978-91-7595-981-8 (ISBN)
##### Presentation
2016-05-23, N111 Kuben, MSE ITM, Brinellvägen 23, KTH-Campus, Stockholm, 13:15 (Engelska)
##### Anmärkning

QC 20160509

Thiyam, P., Lima, E. R., Malyi, O. I., Parsons, D. F., Buhmann, S. Y., Persson, C. & Boström, M. (2016). Effects of van der Waals forces and salt ions on the growth of water films on ice and the detachment of CO2 bubbles. Europhysics letters, 113(4), Article ID 43002.
Öppna denna publikation i ny flik eller fönster >>Effects of van der Waals forces and salt ions on the growth of water films on ice and the detachment of CO2 bubbles
2016 (Engelska)Ingår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 113, nr 4, artikel-id 43002Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

We study the effect of salts on the thickness of wetting films on melting ice and interactions acting on CO2 bubble near ice-water and vapor-water interfaces. Governing mechanisms are the Lifshitz and the double-layer interactions in the respective three-layer geometries. We demonstrate that the latter depend on the Casimir-Polder interaction of the salt ions dissolved in water with the respective ice, vapor and CO2 interfaces, as calculated using different models for their effective polarizability in water. Significant variation in the predicted thickness of the equilibrium water film is observed for different salt ions and when using different models for the ions' polarizabilities. We find that CO2 bubbles are attracted towards the ice-water interface and repelled from the vapor-water interface.

##### Nyckelord
Lifshitz Theory, Hydrocarbon Adsorption, Vanderwaals Forces, Dispersion Forces, Liquid Helium, Surface, Dependence, Systems, Storage
Fysikalisk kemi
##### Identifikatorer
urn:nbn:se:kth:diva-185385 (URN)10.1209/0295-5075/113/43002 (DOI)000372420000012 ()2-s2.0-84962231437 (Scopus ID)
##### Anmärkning

QC 20160418

Malyi, O. I., Bostroem, M., Kulish, V. V., Thiyam, P., Parsons, D. F. & Persson, C. (2016). Volume dependence of the dielectric properties of amorphous SiO2. Physical Chemistry, Chemical Physics - PCCP, 18(10), 7483-7489
Öppna denna publikation i ny flik eller fönster >>Volume dependence of the dielectric properties of amorphous SiO2
2016 (Engelska)Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, nr 10, s. 7483-7489Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Using first principles calculations, the analysis of the dielectric properties of amorphous SiO2 (am-SiO2) was performed. We found that the am-SiO2 properties are volume dependent, and the dependence is mainly induced by the variation of nanoporosity at the atomic scale. In particular, both ionic and electronic contributions to the static dielectric constants are functions of volume with clear trends. Moreover, using the unique parameterization of the dielectric function provided in this work, we predict dielectric functions at imaginary frequencies of different SiO2 polymorphs having similar band gap energies.

Teoretisk kemi
##### Identifikatorer
urn:nbn:se:kth:diva-184522 (URN)10.1039/c5cp06775h (DOI)000371608600062 ()26902661 (PubMedID)2-s2.0-84960146396 (Scopus ID)
##### Anmärkning

QC 20160406

Thiyam, P., Parashar, P., Shajesh, K. V., Persson, C., Schaden, M., Brevik, I., . . . Bostrom, M. (2015). Anisotropic contribution to the van der Waals and the Casimir-Polder energies for CO2 and CH4 molecules near surfaces and thin films. Physical Review A. Atomic, Molecular, and Optical Physics, 92(5), Article ID 052704.
Öppna denna publikation i ny flik eller fönster >>Anisotropic contribution to the van der Waals and the Casimir-Polder energies for CO2 and CH4 molecules near surfaces and thin films
2015 (Engelska)Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, nr 5, artikel-id 052704Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

In order to understand why carbon dioxide (CO2) and methane (CH4) molecules interact differently with surfaces, we investigate the Casimir-Polder energy of a linearly polarizable CO2 molecule and an isotropically polarizable CH4 molecule in front of an atomically thin gold film and an amorphous silica slab. We quantitatively analyze how the anisotropy in the polarizability of the molecule influences the van der Waals contribution to the binding energy of the molecule.

##### Ort, förlag, år, upplaga, sidor
American Physical Society, 2015
Fysik
##### Identifikatorer
urn:nbn:se:kth:diva-177939 (URN)10.1103/PhysRevA.92.052704 (DOI)000364156300004 ()2-s2.0-84946944015 (Scopus ID)
##### Anmärkning

QC 20151203

Thiyam, P., Malyi, O. I., Persson, C., Buhmann, S. Y., Parsons, D. F. & Boström, M. (2015). Effective lennard-jones parameters for CO2-CO2 dispersion interactions in water and near amorphous silica-water interfaces. In: : . Paper presented at Progress in Electromagnetics Research Symposium (pp. 1289-1296). Electromagnetics Academy
Öppna denna publikation i ny flik eller fönster >>Effective lennard-jones parameters for CO2-CO2 dispersion interactions in water and near amorphous silica-water interfaces
2015 (Engelska)Konferensbidrag, Publicerat paper (Refereegranskat)
##### Abstract [en]

Different models for effective polarizability in water and the corresponding dispersion forces between dissolved molecules are explored in bulk water and near interfaces. We demonstrate that the attractive part of the Lennard-Jones parameters, i.e., the van der Waals parameter C6 (UvdW ≈ -C6/ρ6), is strongly modified when two carbon dioxide (CO2) molecules are near an amorphous silica-water and near a vapor-water interface. Standard simulation parameters for near-surface modeling are based on intermolecular forces in bulk media.

##### Nyckelord
Amorphous carbon, Carbon, Chemical bonds, Dispersions, Molecules, Silica, Van der Waals forces, Amorphous silica, Dispersion force, Dispersion interaction, Inter-molecular forces, Lennard-Jones parameters, Polarizabilities, Simulation parameters, Van der waals, Carbon dioxide
Fysikalisk kemi
##### Identifikatorer
urn:nbn:se:kth:diva-181587 (URN)2-s2.0-84947259599 (Scopus ID)9781934142301 (ISBN)
##### Konferens
Progress in Electromagnetics Research Symposium
##### Anmärkning

QC 20160311

Boström, M., Dou, M., Thiyam, P., Parsons, D. F., Malyi, O. I. & Persson, C. (2015). Increased porosity turns desorption to adsorption for gas bubbles near water-SiO2 interface. Physical Review B. Condensed Matter and Materials Physics, 91(7), Article ID 075403.
Öppna denna publikation i ny flik eller fönster >>Increased porosity turns desorption to adsorption for gas bubbles near water-SiO2 interface
2015 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, nr 7, artikel-id 075403Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

We consider theoretically the retarded van der Waals interaction of a small gas bubble in water with a porous SiO2 surface. We predict a possible transition from repulsion to attraction as the surface is made more porous. It highlights that bubbles will interact differently with surface regions with different porosity (i.e., with different optical properties).

##### Identifikatorer
urn:nbn:se:kth:diva-161107 (URN)10.1103/PhysRevB.91.075403 (DOI)000348873500003 ()2-s2.0-84961288284 (Scopus ID)
##### Forskningsfinansiär
Vetenskapsrådet, C0485101

QC 20150323

##### Identifikatorer
ORCID-id: orcid.org/0000-0002-5249-0211

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